Original Article
Correspondence of physical activity and fruit/vegetable consumption among prostate cancer survivors and their spouses S. MYERS VIRTUE, PSY.D, INSTRUCTOR, ASSISTANT PROFESSOR, Department of Population Science, Rutgers Cancer Institute of New Jersey, New Brunswick, NJ, and Temple University Kornberg School of Dentistry, Philadelphia, PA, S.L. MANNE, PHD, PROFESSOR, Department of Population Science, Rutgers Cancer Institute of New Jersey, New Brunswick, NJ, D. KASHY, PHD, PROFESSOR, Department of Psychology, Michigan State University, East Lansing, MI, C.J. HECKMAN, PHD, ASSOCIATE PROFESSOR, Cancer Prevention and Control Program, Fox Chase Cancer Center, Philadelphia, PA, T. ZAIDER, PHD, ATTENDING PSYCHOLOGIST, Department of Psychiatry and Behavioral Sciences, Memorial Sloan-Kettering Cancer Center, New York, NY, D.W. KISSANE MD, PROFESSOR, Department of Psychiatry, Monash University, Melbourne, Vic. Australia, I. KIM, MD, CHIEF, Section of Urologic Oncology, Rutgers Cancer Institute of New Jersey, New Brunswick, NJ, D. LEE, MD, CHIEF, Division of Urology, Hospital of the University of Pennsylvania, Perelman Center for Advanced Medicine, Philadelphia, PA, & G. OLEKSON, MA, ASSISTANT PROGRAM MANAGER, Department of Population Science, Rutgers Cancer Institute of New Jersey, New Brunswick, NJ, USA MYERS VIRTUE S., MANNE S.L., KASHY D., HECKMAN C.J., ZAIDER T., KISSANE D.W., KIM I., LEE D. & OLEKSON G. (2015) European Journal of Cancer Care 24, 827–839 Correspondence of physical activity and fruit/vegetable consumption among prostate cancer survivors and their spouses A healthy diet and physical activity are recommended for prostate cancer survivors. Interdependence theory suggests that the spousal relationship influences those health behaviours and the degree of correspondence may be an indicator of this influence. This study evaluated the correspondence between prostate cancer survivors and spouses regarding physical activity and fruit/vegetable consumption. Baseline data from an ongoing randomised control trial were utilised. Men who had been treated for prostate cancer within the past year and their partners (N = 132 couples) completed self-report measures of physical activity, fruit/ vegetable consumption, relationship satisfaction and support for partner’s healthy diet and physical activity. Couples reported similar fruit/vegetable consumption and physical activity as indicated by high levels of correspondence. Greater fruit/vegetable correspondence was related to higher relationship satisfaction (F = 4.14, P = 0.018) and greater patient (F = 13.29, P < 0.001) and spouse-rated support (F = 7.2, P < 0.001). Greater physical activity correspondence was related to greater patient (F = 3.57, P = 0.028) and spouse-rated support (F = 4.59, P = 0.031). Prostate cancer survivors and spouses may influence each other’s diet and exercise behaviours. Couple-based interventions may promote healthy behaviours among this population.
Keywords: prostate cancer, couples, exercise, nutrition.
Correspondence address: Shannon Myers Virtue, Department of Population Science, Rutgers Cancer Institute of New Jersey, 195 Little Albany Street, New Brunswick, NJ, USA (e-mail: [email protected]. edu; [email protected]).
Accepted 24 February 2015 DOI: 10.1111/ecc.12316 European Journal of Cancer Care, 2015, 24, 827–839
© 2015 John Wiley & Sons Ltd
I N TR O DU C TI O N Prostate cancer is the most common cancer in the United States, excluding skin cancers (American Cancer Society 2014). Improvements in screening and treatment have led to early detection and positive treatment outcomes. The
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estimated 5-year survival rate in the US is approximately 99% (National Cancer Institute 2009). Since the population of prostate cancer survivors is large and growing, optimal health and quality of life among prostate cancer survivors is an important public health goal. Key components of health among prostate cancer survivors are physical activity and diet (Doyle et al. 2006; Keogh & MacLeod 2012). There are recommended guidelines for both physical activity and diet which may promote health among prostate cancer survivors. In terms of physical activity, recommendations for the general adult population are to engage in at least 150 min of moderate or 75 min of vigorous activity per week (Haskell et al. 2007; Schmitz et al. 2010). Among the prostate cancer survivors, there is evidence that adherence to these physical activity guidelines is correlated with beneficial health effects, such as better health-related quality of life (Blanchard et al. 2004, 2008) and less incontinence after radical prostatectomy (Mina et al. 2014). Despite the health benefits, only 30% (Bellizzi et al. 2005) to 43% (Blanchard et al. 2008) of prostate cancer survivors meet the recommended physical activity guidelines. In terms of a healthy diet, the dietary guideline for the general adult population is to consume at least five servings of fruits and vegetables per day (Center for Nutrition Policy & Promotion 2005). Prostate cancer survivors who adhere to the recommended five servings have better health-related quality of life (Blanchard et al. 2008) and physical functioning (Demark-Wahnefried et al. 2004). Adherence to dietary guidelines is also relatively low, with estimates suggesting that between 16% (Blanchard et al. 2008) and 35% (Demark-Wahnefried et al. 2000) of prostate cancer survivors consume the recommended five servings of fruits and vegetables each day. While there have been studies examining prostate cancer survivors’ adherence to these guidelines, little is known about the health behaviours of their spouses and whether the health behaviours of survivors and spouses are related. There are many factors that may influence cancer survivors’ adherence to recommended physical activity and dietary guidelines, including a physician recommendation (Satia et al. 2009), higher levels of self-efficacy (Pinto et al. 2009), and higher levels of behavioural control (Courneya et al. 2002). One little-studied but important factor is the influence of one’s spouse. Relationship theories, such as the Interdependence theory (Lewis et al. 2006) provide a framework for understanding how partners may influence each other’s health behaviours. Interdependence theory suggests that in dyads one person’s behaviour is not free from the influence of the partner’s behaviour (Lewis et al. 2002). The influence of one’s partner on one’s own 828
behaviour is referred to as partner effects (Lewis et al. 2006) which can be can be health-compromising or health-enhancing (Lewis et al. 2002). Health-enhancing influence is more likely when the behaviour change is viewed as meaningful and beneficial for the relationship (Lewis et al. 2006). The theory refers to this process as transformation of motivation, which occurs when couples interpret a health behaviour as beneficial or meaningful for the relationship and one’s partner (e.g. adopting a relationship perspective), leading to changes in behaviour which are health-enhancing (Lewis et al. 2006). An indicator of partner influence and a key construct in Interdependence theory is the degree of correspondence between couples’ behaviours (Lewis et al. 2002, 2006). Correspondence is measured as the degree of agreement between partners’ health behaviours, and it is valuable because the degree of correspondence can facilitate the couple’s focus on values, motivations and barriers related to health behaviour change (Lewis et al. 2002). High correspondence occurs when partners are cooperative and in agreement that they should address a desired behaviour. Low correspondence, or discordance, occurs when partners are in conflict about whether to engage in a health behaviour (Lewis et al. 2002). Research has indicated a high degree of agreement in the general population between partners’ health behaviours, including levels of physical activity, diet, alcohol consumption and smoking (Wilson 2002; Stimpson et al. 2006; Meyler et al. 2007). There is also evidence that couples tend to correspond with regard to health care practices such as skin cancer screening (Heckman et al. 2013). Furthermore, longitudinal data suggest that when one partner improves his or her health behaviours, the other partner is also likely to do so (Falba & Sindelar 2008). The time period following the diagnosis of cancer may be a period when partners’ influence on one another’s health behaviour becomes stronger. Thus, higher levels of correspondence between partners’ health behaviours would be expected. According to Interdependence theory (Lewis et al. 2006), couples facing a health threat may respond with communal coping efforts. Communal coping refers to couples developing a joint view of a health threat and a shared plan to manage the threat (Lyons et al. 1998; Lewis et al. 2002). The time following a cancer diagnosis is often referred to as a ‘teachable moment’, when both survivors and members of their families are motivated to make health behaviour changes (McBride et al. 2000; Schnoll et al. 2013). The idea that a health threat prompts health-enhancing behaviours is supported by research indicating that greater cancer-related distress is associated with positive health behaviour changes among cancer © 2015 John Wiley & Sons Ltd
Correspondence among prostate cancer couples
survivors, including diet, exercise, and smoking (Mullens et al. 2004; Park & Gaffey 2007). Greater correspondence during this time period may assist couples in focusing on motivation and making decisions about health behaviours (Lewis et al. 2002). Little is known about the degree of correspondence in diet and physical activity practices of prostate cancer survivors and their spouses and the influence of relationshiplevel (e.g. marital quality) and individual-level (e.g. cancer distress) factors upon couples’ correspondence. The present study addressed these gaps in the research literature by examining physical activity and fruit/vegetable consumption among prostate cancer survivors and their spouses. The study had two specific aims. The first study aim was to explore the degree of correspondence among prostate cancer survivors and spouses with regard to their physical activity and fruit and vegetable consumption. Couples’ correspondence was placed into three categories. First, couples were considered positively concordant, meaning both partners met required physical activity (or fruit and vegetable consumption) guidelines. Second, couples were considered negatively concordant, meaning neither partner met required physical activity (or fruit and vegetable consumption) guidelines. Third, couples were considered discordant, which was defined as one partner met required guidelines for each health behaviour and one partner did not. We calculated the proportion of couples that were positively concordant, negatively concordant, and discordant for both physical activity and fruit and vegetable consumption guidelines. Based on prior research and Interdependence theory, we hypothesised that most couples would have high levels of either positive or negative concordance for fruit and vegetable consumption and physical activity. The second study aim was to examine relationship-level and individual-level factors associated with couple correspondence. In terms of relationship factors, according to Interdependence theory, positive support within the relationship for health behaviour change is necessary for change to occur (Lewis et al. 2006). Partners in higher quality relationships are more likely to accept one another’s input and influence, and thereby make behaviour changes (Lewis et al. 2002). Indeed, better relationship quality has been linked to better health practices (Wickrama et al. 1997). Therefore, we hypothesised greater relationship satisfaction and more support for one’s partner’s healthy diet and engaging in regular physical activity would be associated with positive couple concordance. In terms of individual-level factors, some studies suggest that higher levels of cancer-related distress predict positive health behaviour changes among cancer survivors (Park & Gaffey 2007). Therefore, we hypothes© 2015 John Wiley & Sons Ltd
ised that survivor or spouse cancer-related distress would serve as a motivator for healthy behaviours among couples and would therefore be associated with positive couple concordance. Other individual-level factors evaluated as possible correlates of couple correspondence included demographic (e.g. age, number of years in the relationship) and medical variables (e.g. disease stage). METHOD Participants and procedures The study utilised baseline data from a multi-site, ongoing randomised clinical trial (RCT) examining couple-focused interventions for men diagnosed with prostate cancer and their spouses (second author, unpublished data). Participants were 132 couples in which one partner had been diagnosed with localised prostate cancer and treated within 12 months of recruitment to the study. For clarity, we use the term ‘spouse’ to denote the survivors’ partner, even though there are some partners in the study who were not married to the survivor. Eligibility criteria for the RCT were (1) survivor had a primary diagnosis of localised prostate cancer, (2) survivor had surgery and/or radiation treatment for localised prostate cancer within the last 12 months, (3) couples were married or cohabitating for ≥1 year, (4) both partners were ≥18 years, (5) survivor or spouse indicated elevated levels of cancer-specific distress, defined as a score of >15 for survivors or >16 for spouses on the Impact of Events Scales (IES; Horowitz et al. 1979), at the time of recruitment (due to eligibility for RCT), (6) neither partner had significant hearing impairment which would have precluded intervention participation, (7) lived within 1 h commuting distance from the centre and (8) both partners completed informed consent. Prostate cancer survivors were identified at four comprehensive cancer centres in the Northeastern United States. Research assistants at each site approached eligible couples about participation in the larger study either in person during an outpatient visit or by telephone. The survivor and spouse were given an informed consent form approved by the Institutional Review Board (IRB) at each site and a baseline survey with a stamped return envelope to complete the forms and return by mail. Couples were paid $50 for completing the baseline survey. IRB approval was obtained prior to the study. The research was conducted in accordance with the ethical standards of the responsible committee on human experimentation (institutional and national) and with the Helsinki Declaration of 1975, as revised in 2000. Of the 688 eligible couples approached for the RCT, 132 (19%) signed consent forms and completed baseline 829
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surveys. The most common reasons provided for refusing participation in the RCT were ‘not needing help’ or ‘not perceiving any benefit to participating’ (16%), ‘being too busy’ (14%) and ‘no interest’ (12%). The participation rate is comparable to reported rates for other couples-based intervention studies with cancer patients (Manne et al. 2014). Comparisons between survivor participants and refusers were made with regard to available data (age, race, disease stage and time since diagnosis). Participants were diagnosed with significantly higher cancer stage compared to refusers [t (222) = 3.42, P = 0.001].
multiplying consumption frequency by portion size. Prior research suggests that test–retest reliability as measured by reproducibility of reports over a 1-year period of time are high (0.80 and 0.79 respectively). In terms of validity, the correlations between self-reported fruit and vegetable consumption and plasma carotenoids and vitamin C at baseline were 0.39, and 0.37 for fruits and 0.28 and 0.30 for vegetables, which is a reasonable figure (Bogers et al. 2004). For the purposes of the present study, the daily fruit/vegetable consumption was computed into a dichotomous variable (yes/no) indicating whether the individual met recommended weekly guidelines (i.e. consumed ≥5 servings).
Measures Demographic and medical information
Relationship satisfaction
The baseline survey collected data on survivor and spouse age, race, education, income, marital status, occupational status (working vs. not working) and length of relationship. Data on disease stage, treatment (e.g. radical prostatectomy, radiation), time from diagnosis, and Gleason score were obtained through medical chart review. The Gleason score is a system of grading prostate cancer. Scores range from 2 to 10 and indicate the likelihood that a tumour will spread. A higher score indicates that cancer tissue is more abnormal and likely to spread (National Cancer Institute 2015).
The Dyadic Adjustment Scale (Spanier & Filsinger 1983) was utilised to assess relationship satisfaction. The scale consists of 32 items. Higher scores indicate higher levels of satisfaction. Sample items include ‘In general, how often do you think that things between your partner are going well?’ and ‘Do you and your mate engage in outside interests together?’ The scale has been widely used and has shown strong psychometric properties in prior use with couples coping with cancer (Manne et al. 2006). Internal consistency in the present study was excellent for survivors (a = 0.94) and spouses (a = 0.94).
Physical activity
Partner support for physical activity and fruit and vegetable consumption
The Godin Leisure Time Exercise Questionnaire (GLTEQ; Godin & Shephard 1985) was utilised to assess physical activity. The GLTEQ contains three questions about the average weekly duration of engagement in strenuous/vigorous, moderate and mild physical activity over the past month. Reliability and validity of the measure has been strong (Jacobs et al. 1993). For the purposes of the present study, the average weekly physical activity was computed into a dichotomous variable (yes/no) indicating whether the individual met recommended weekly physical activity guidelines (i.e. 150 min of moderate or 75 min of vigorous or a combination of vigorous/moderate per week). This calculation method has been utilised in prior work with prostate cancer patients (Mina et al. 2014).
Fruit and vegetable consumption An eight item self-report assessment of intake of fruits and vegetables in the past week was utilised to assess consumption (Bogers et al. 2004). Fruit and Vegetable Consumption was calculated in servings per day by 830
A 5-item measure adapted from Butterfield and Lewis (2002) was utilised to assess the level of partner support for engagement in regular physical activity and consuming more fruits and vegetables. Items assess the degree of support for partner’s healthy diet and physical activity, the importance of partner’s healthy diet and physical activity, frequency of discussions as a couple about a healthy diet and physical activity, the degree of support provided to one another during the discussion (s), and perception of the quality of the discussion(s). Sample items include ‘To what degree do you support your partner in having a healthy diet and being physically active?’ and ‘If you talked at all about having a healthy diet and engaging in physical activity with your partner, how supportive were you to one another?’ Responses were made on a Likert-type scale and total scores range from 4 to 20 with higher scores indicating greater supportiveness. Internal consistency for the present study was acceptable for survivors (a = 0.73) and spouses (a = 0.79). © 2015 John Wiley & Sons Ltd
Correspondence among prostate cancer couples
Cancer-related distress The IES (Horowitz et al. 1979) assessed psychological distress related to the prostate cancer. The IES is a 22-item self-report measure focusing on intrusive thoughts, avoidance behaviours, and hyperarousal symptoms associated with a stressor, in this case prostate cancer. Sample items include, ‘I thought about it when I didn’t mean to’ and ‘I tried to remove it from my memory’. Participants rated how true each statement was for them during the past week using a 6-point Likert scales (0 = Not at all; 5 = Often). Scores range from 0 to 110. The measure was completed at the time of the baseline survey. The scale has been widely used as a measure of cancer distress (Baider et al. 2003). Internal consistency for the present study was acceptable for survivors (a = 0.92) and spouses (a = 0.94). Analysis plan To address the first aim, we utilised dichotomous variables indicating whether each partner met recommended guidelines for fruit/vegetable consumption and physical activity. As previously described, couples were labelled as positively concordant, negatively concordant or discordant. There were nine couples in which one partner did not have complete data for the fruit/vegetable measure and seven couples in which one partner did not have complete data for the physical activity measure. Correspondence was only computed for couples with complete data for fruit/vegetable guidelines (n = 123) and physical activity guidelines (n = 125). The overall proportion of correspondence was calculated and Cohen’s Kappa was utilised to determine whether the level of similarity was larger than what would be expected to occur by chance. To address the second aim, chi-squared analyses were conducted to examine differences in concordance patterns for both fruit/vegetable guidelines and physical activity guidelines as a function of possible covariates, which included survivor race, couples’ employment status (both working, one partner working, or neither partner working), and type of treatment (surgery vs. radiation). Analysis of variance analyses were conducted to examine mean differences between the three groups (i.e. positively concordant, negatively concordant, discordant) on demographic (survivor age, survivor education, spouse age, spouse education, household income, length of relationship), medical (stage of cancer, time from diagnosis, Gleason score), and relationship (survivor relationship satisfaction, spouse relationship satisfaction, survivor-rated support for spouse’s engagement in © 2015 John Wiley & Sons Ltd
healthy diet and regular physical activity, spouse-rated support for patient’s engagement in healthy diet and physical activity) factors, as well as level of cancerrelated distress. RESULTS Participant characteristics The sample consisted of 132 couples. The mean age was 61 years for survivors and 57 years for spouses. The majority of survivors was White (78%) and had completed college or graduate school (68%). The majority of spouses was White (76%) and had completed at least some college education (61%). Most couples were married (96%). In approximately half of the couples, both partners were working part or full time (54%). There were two same-sex couples in the sample. The mean length of the couples’ relationship was 27 years. The average time since the prostate cancer diagnosis was 10 months (range = 2– 26 months). The complete characteristics of the sample are presented in Table 1. In total, 68% (n = 174/255) of the entire sample met fruit/vegetable guidelines and 56% (n = 143/256) met physical activity guidelines. Among survivors, 72% (n = 92/127) met the fruit/vegetable guidelines and 60% (n = 78/129) met physical activity guidelines. Among spouses, 64% (n = 82/128) met the fruit/vegetable guidelines and 51% (n = 65/127) met physical activity guidelines. Logistic regressions were utilised to examine individual-level and relationship-level factors associated with whether a survivor or spouse met fruit/vegetable or physical activity guidelines. Among survivors, meeting fruit/vegetables guidelines was associated with Caucasian race [Wald v2(1) = 6.72, P = 0.01, odds ratio = 10.57, 95% CI 1.78–62.83] and greater spouse-reported partner support [Wald v2(1) = 5.59, P = 0.018, odds ratio = 0.59, 95% CI 0.38–0.91]. Meeting physical activity guidelines was associated with greater time from diagnosis [Wald v2(1) = 4.41, P = 0.036, odds ratio = 1.19, 95% CI 1.01–1.41], greater survivor-reported partner support [Wald v2(1) = 5.02, P = 0.025, odds ratio = 1.47, 95% CI 1.05–2.07], and greater spouse-reported partner support [Wald v2(1) = 4.24, P = 0.04, odds ratio = 1.38, 95% CI 1.02–1.86]. Among spouses, meeting fruit/vegetable guidelines for spouses was not associated with any individual-level or relationship-level factors, but meeting physical activity guidelines was associated with greater survivor-reported cancer distress [Wald v2(1) = 7.71, P = 0.005, odds ratio = 1.05, 95% CI 1.02–1.09]. Descriptive analyses of survivors, spouses, and total sample in terms of physical activity and fruit and vegetable guidelines are presented in Table 2. 831
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Table 1. Characteristics of study sample Variable Age (years) Race White/Caucasian Black/African-American Asian Hispanic/Latino Other Education
Correspondence of physical activity and fruit/vegetable consumption among prostate cancer survivors and their spouses S. MYERS VIRTUE, PSY.D, INSTRUCTOR, ASSISTANT PROFESSOR, Department of Population Science, Rutgers Cancer Institute of New Jersey, New Brunswick, NJ, and Temple University Kornberg School of Dentistry, Philadelphia, PA, S.L. MANNE, PHD, PROFESSOR, Department of Population Science, Rutgers Cancer Institute of New Jersey, New Brunswick, NJ, D. KASHY, PHD, PROFESSOR, Department of Psychology, Michigan State University, East Lansing, MI, C.J. HECKMAN, PHD, ASSOCIATE PROFESSOR, Cancer Prevention and Control Program, Fox Chase Cancer Center, Philadelphia, PA, T. ZAIDER, PHD, ATTENDING PSYCHOLOGIST, Department of Psychiatry and Behavioral Sciences, Memorial Sloan-Kettering Cancer Center, New York, NY, D.W. KISSANE MD, PROFESSOR, Department of Psychiatry, Monash University, Melbourne, Vic. Australia, I. KIM, MD, CHIEF, Section of Urologic Oncology, Rutgers Cancer Institute of New Jersey, New Brunswick, NJ, D. LEE, MD, CHIEF, Division of Urology, Hospital of the University of Pennsylvania, Perelman Center for Advanced Medicine, Philadelphia, PA, & G. OLEKSON, MA, ASSISTANT PROGRAM MANAGER, Department of Population Science, Rutgers Cancer Institute of New Jersey, New Brunswick, NJ, USA MYERS VIRTUE S., MANNE S.L., KASHY D., HECKMAN C.J., ZAIDER T., KISSANE D.W., KIM I., LEE D. & OLEKSON G. (2015) European Journal of Cancer Care 24, 827–839 Correspondence of physical activity and fruit/vegetable consumption among prostate cancer survivors and their spouses A healthy diet and physical activity are recommended for prostate cancer survivors. Interdependence theory suggests that the spousal relationship influences those health behaviours and the degree of correspondence may be an indicator of this influence. This study evaluated the correspondence between prostate cancer survivors and spouses regarding physical activity and fruit/vegetable consumption. Baseline data from an ongoing randomised control trial were utilised. Men who had been treated for prostate cancer within the past year and their partners (N = 132 couples) completed self-report measures of physical activity, fruit/ vegetable consumption, relationship satisfaction and support for partner’s healthy diet and physical activity. Couples reported similar fruit/vegetable consumption and physical activity as indicated by high levels of correspondence. Greater fruit/vegetable correspondence was related to higher relationship satisfaction (F = 4.14, P = 0.018) and greater patient (F = 13.29, P < 0.001) and spouse-rated support (F = 7.2, P < 0.001). Greater physical activity correspondence was related to greater patient (F = 3.57, P = 0.028) and spouse-rated support (F = 4.59, P = 0.031). Prostate cancer survivors and spouses may influence each other’s diet and exercise behaviours. Couple-based interventions may promote healthy behaviours among this population.
Keywords: prostate cancer, couples, exercise, nutrition.
Correspondence address: Shannon Myers Virtue, Department of Population Science, Rutgers Cancer Institute of New Jersey, 195 Little Albany Street, New Brunswick, NJ, USA (e-mail: [email protected]. edu; [email protected]).
Accepted 24 February 2015 DOI: 10.1111/ecc.12316 European Journal of Cancer Care, 2015, 24, 827–839
© 2015 John Wiley & Sons Ltd
I N TR O DU C TI O N Prostate cancer is the most common cancer in the United States, excluding skin cancers (American Cancer Society 2014). Improvements in screening and treatment have led to early detection and positive treatment outcomes. The
MYERS VIRTUE ET AL.
estimated 5-year survival rate in the US is approximately 99% (National Cancer Institute 2009). Since the population of prostate cancer survivors is large and growing, optimal health and quality of life among prostate cancer survivors is an important public health goal. Key components of health among prostate cancer survivors are physical activity and diet (Doyle et al. 2006; Keogh & MacLeod 2012). There are recommended guidelines for both physical activity and diet which may promote health among prostate cancer survivors. In terms of physical activity, recommendations for the general adult population are to engage in at least 150 min of moderate or 75 min of vigorous activity per week (Haskell et al. 2007; Schmitz et al. 2010). Among the prostate cancer survivors, there is evidence that adherence to these physical activity guidelines is correlated with beneficial health effects, such as better health-related quality of life (Blanchard et al. 2004, 2008) and less incontinence after radical prostatectomy (Mina et al. 2014). Despite the health benefits, only 30% (Bellizzi et al. 2005) to 43% (Blanchard et al. 2008) of prostate cancer survivors meet the recommended physical activity guidelines. In terms of a healthy diet, the dietary guideline for the general adult population is to consume at least five servings of fruits and vegetables per day (Center for Nutrition Policy & Promotion 2005). Prostate cancer survivors who adhere to the recommended five servings have better health-related quality of life (Blanchard et al. 2008) and physical functioning (Demark-Wahnefried et al. 2004). Adherence to dietary guidelines is also relatively low, with estimates suggesting that between 16% (Blanchard et al. 2008) and 35% (Demark-Wahnefried et al. 2000) of prostate cancer survivors consume the recommended five servings of fruits and vegetables each day. While there have been studies examining prostate cancer survivors’ adherence to these guidelines, little is known about the health behaviours of their spouses and whether the health behaviours of survivors and spouses are related. There are many factors that may influence cancer survivors’ adherence to recommended physical activity and dietary guidelines, including a physician recommendation (Satia et al. 2009), higher levels of self-efficacy (Pinto et al. 2009), and higher levels of behavioural control (Courneya et al. 2002). One little-studied but important factor is the influence of one’s spouse. Relationship theories, such as the Interdependence theory (Lewis et al. 2006) provide a framework for understanding how partners may influence each other’s health behaviours. Interdependence theory suggests that in dyads one person’s behaviour is not free from the influence of the partner’s behaviour (Lewis et al. 2002). The influence of one’s partner on one’s own 828
behaviour is referred to as partner effects (Lewis et al. 2006) which can be can be health-compromising or health-enhancing (Lewis et al. 2002). Health-enhancing influence is more likely when the behaviour change is viewed as meaningful and beneficial for the relationship (Lewis et al. 2006). The theory refers to this process as transformation of motivation, which occurs when couples interpret a health behaviour as beneficial or meaningful for the relationship and one’s partner (e.g. adopting a relationship perspective), leading to changes in behaviour which are health-enhancing (Lewis et al. 2006). An indicator of partner influence and a key construct in Interdependence theory is the degree of correspondence between couples’ behaviours (Lewis et al. 2002, 2006). Correspondence is measured as the degree of agreement between partners’ health behaviours, and it is valuable because the degree of correspondence can facilitate the couple’s focus on values, motivations and barriers related to health behaviour change (Lewis et al. 2002). High correspondence occurs when partners are cooperative and in agreement that they should address a desired behaviour. Low correspondence, or discordance, occurs when partners are in conflict about whether to engage in a health behaviour (Lewis et al. 2002). Research has indicated a high degree of agreement in the general population between partners’ health behaviours, including levels of physical activity, diet, alcohol consumption and smoking (Wilson 2002; Stimpson et al. 2006; Meyler et al. 2007). There is also evidence that couples tend to correspond with regard to health care practices such as skin cancer screening (Heckman et al. 2013). Furthermore, longitudinal data suggest that when one partner improves his or her health behaviours, the other partner is also likely to do so (Falba & Sindelar 2008). The time period following the diagnosis of cancer may be a period when partners’ influence on one another’s health behaviour becomes stronger. Thus, higher levels of correspondence between partners’ health behaviours would be expected. According to Interdependence theory (Lewis et al. 2006), couples facing a health threat may respond with communal coping efforts. Communal coping refers to couples developing a joint view of a health threat and a shared plan to manage the threat (Lyons et al. 1998; Lewis et al. 2002). The time following a cancer diagnosis is often referred to as a ‘teachable moment’, when both survivors and members of their families are motivated to make health behaviour changes (McBride et al. 2000; Schnoll et al. 2013). The idea that a health threat prompts health-enhancing behaviours is supported by research indicating that greater cancer-related distress is associated with positive health behaviour changes among cancer © 2015 John Wiley & Sons Ltd
Correspondence among prostate cancer couples
survivors, including diet, exercise, and smoking (Mullens et al. 2004; Park & Gaffey 2007). Greater correspondence during this time period may assist couples in focusing on motivation and making decisions about health behaviours (Lewis et al. 2002). Little is known about the degree of correspondence in diet and physical activity practices of prostate cancer survivors and their spouses and the influence of relationshiplevel (e.g. marital quality) and individual-level (e.g. cancer distress) factors upon couples’ correspondence. The present study addressed these gaps in the research literature by examining physical activity and fruit/vegetable consumption among prostate cancer survivors and their spouses. The study had two specific aims. The first study aim was to explore the degree of correspondence among prostate cancer survivors and spouses with regard to their physical activity and fruit and vegetable consumption. Couples’ correspondence was placed into three categories. First, couples were considered positively concordant, meaning both partners met required physical activity (or fruit and vegetable consumption) guidelines. Second, couples were considered negatively concordant, meaning neither partner met required physical activity (or fruit and vegetable consumption) guidelines. Third, couples were considered discordant, which was defined as one partner met required guidelines for each health behaviour and one partner did not. We calculated the proportion of couples that were positively concordant, negatively concordant, and discordant for both physical activity and fruit and vegetable consumption guidelines. Based on prior research and Interdependence theory, we hypothesised that most couples would have high levels of either positive or negative concordance for fruit and vegetable consumption and physical activity. The second study aim was to examine relationship-level and individual-level factors associated with couple correspondence. In terms of relationship factors, according to Interdependence theory, positive support within the relationship for health behaviour change is necessary for change to occur (Lewis et al. 2006). Partners in higher quality relationships are more likely to accept one another’s input and influence, and thereby make behaviour changes (Lewis et al. 2002). Indeed, better relationship quality has been linked to better health practices (Wickrama et al. 1997). Therefore, we hypothesised greater relationship satisfaction and more support for one’s partner’s healthy diet and engaging in regular physical activity would be associated with positive couple concordance. In terms of individual-level factors, some studies suggest that higher levels of cancer-related distress predict positive health behaviour changes among cancer survivors (Park & Gaffey 2007). Therefore, we hypothes© 2015 John Wiley & Sons Ltd
ised that survivor or spouse cancer-related distress would serve as a motivator for healthy behaviours among couples and would therefore be associated with positive couple concordance. Other individual-level factors evaluated as possible correlates of couple correspondence included demographic (e.g. age, number of years in the relationship) and medical variables (e.g. disease stage). METHOD Participants and procedures The study utilised baseline data from a multi-site, ongoing randomised clinical trial (RCT) examining couple-focused interventions for men diagnosed with prostate cancer and their spouses (second author, unpublished data). Participants were 132 couples in which one partner had been diagnosed with localised prostate cancer and treated within 12 months of recruitment to the study. For clarity, we use the term ‘spouse’ to denote the survivors’ partner, even though there are some partners in the study who were not married to the survivor. Eligibility criteria for the RCT were (1) survivor had a primary diagnosis of localised prostate cancer, (2) survivor had surgery and/or radiation treatment for localised prostate cancer within the last 12 months, (3) couples were married or cohabitating for ≥1 year, (4) both partners were ≥18 years, (5) survivor or spouse indicated elevated levels of cancer-specific distress, defined as a score of >15 for survivors or >16 for spouses on the Impact of Events Scales (IES; Horowitz et al. 1979), at the time of recruitment (due to eligibility for RCT), (6) neither partner had significant hearing impairment which would have precluded intervention participation, (7) lived within 1 h commuting distance from the centre and (8) both partners completed informed consent. Prostate cancer survivors were identified at four comprehensive cancer centres in the Northeastern United States. Research assistants at each site approached eligible couples about participation in the larger study either in person during an outpatient visit or by telephone. The survivor and spouse were given an informed consent form approved by the Institutional Review Board (IRB) at each site and a baseline survey with a stamped return envelope to complete the forms and return by mail. Couples were paid $50 for completing the baseline survey. IRB approval was obtained prior to the study. The research was conducted in accordance with the ethical standards of the responsible committee on human experimentation (institutional and national) and with the Helsinki Declaration of 1975, as revised in 2000. Of the 688 eligible couples approached for the RCT, 132 (19%) signed consent forms and completed baseline 829
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surveys. The most common reasons provided for refusing participation in the RCT were ‘not needing help’ or ‘not perceiving any benefit to participating’ (16%), ‘being too busy’ (14%) and ‘no interest’ (12%). The participation rate is comparable to reported rates for other couples-based intervention studies with cancer patients (Manne et al. 2014). Comparisons between survivor participants and refusers were made with regard to available data (age, race, disease stage and time since diagnosis). Participants were diagnosed with significantly higher cancer stage compared to refusers [t (222) = 3.42, P = 0.001].
multiplying consumption frequency by portion size. Prior research suggests that test–retest reliability as measured by reproducibility of reports over a 1-year period of time are high (0.80 and 0.79 respectively). In terms of validity, the correlations between self-reported fruit and vegetable consumption and plasma carotenoids and vitamin C at baseline were 0.39, and 0.37 for fruits and 0.28 and 0.30 for vegetables, which is a reasonable figure (Bogers et al. 2004). For the purposes of the present study, the daily fruit/vegetable consumption was computed into a dichotomous variable (yes/no) indicating whether the individual met recommended weekly guidelines (i.e. consumed ≥5 servings).
Measures Demographic and medical information
Relationship satisfaction
The baseline survey collected data on survivor and spouse age, race, education, income, marital status, occupational status (working vs. not working) and length of relationship. Data on disease stage, treatment (e.g. radical prostatectomy, radiation), time from diagnosis, and Gleason score were obtained through medical chart review. The Gleason score is a system of grading prostate cancer. Scores range from 2 to 10 and indicate the likelihood that a tumour will spread. A higher score indicates that cancer tissue is more abnormal and likely to spread (National Cancer Institute 2015).
The Dyadic Adjustment Scale (Spanier & Filsinger 1983) was utilised to assess relationship satisfaction. The scale consists of 32 items. Higher scores indicate higher levels of satisfaction. Sample items include ‘In general, how often do you think that things between your partner are going well?’ and ‘Do you and your mate engage in outside interests together?’ The scale has been widely used and has shown strong psychometric properties in prior use with couples coping with cancer (Manne et al. 2006). Internal consistency in the present study was excellent for survivors (a = 0.94) and spouses (a = 0.94).
Physical activity
Partner support for physical activity and fruit and vegetable consumption
The Godin Leisure Time Exercise Questionnaire (GLTEQ; Godin & Shephard 1985) was utilised to assess physical activity. The GLTEQ contains three questions about the average weekly duration of engagement in strenuous/vigorous, moderate and mild physical activity over the past month. Reliability and validity of the measure has been strong (Jacobs et al. 1993). For the purposes of the present study, the average weekly physical activity was computed into a dichotomous variable (yes/no) indicating whether the individual met recommended weekly physical activity guidelines (i.e. 150 min of moderate or 75 min of vigorous or a combination of vigorous/moderate per week). This calculation method has been utilised in prior work with prostate cancer patients (Mina et al. 2014).
Fruit and vegetable consumption An eight item self-report assessment of intake of fruits and vegetables in the past week was utilised to assess consumption (Bogers et al. 2004). Fruit and Vegetable Consumption was calculated in servings per day by 830
A 5-item measure adapted from Butterfield and Lewis (2002) was utilised to assess the level of partner support for engagement in regular physical activity and consuming more fruits and vegetables. Items assess the degree of support for partner’s healthy diet and physical activity, the importance of partner’s healthy diet and physical activity, frequency of discussions as a couple about a healthy diet and physical activity, the degree of support provided to one another during the discussion (s), and perception of the quality of the discussion(s). Sample items include ‘To what degree do you support your partner in having a healthy diet and being physically active?’ and ‘If you talked at all about having a healthy diet and engaging in physical activity with your partner, how supportive were you to one another?’ Responses were made on a Likert-type scale and total scores range from 4 to 20 with higher scores indicating greater supportiveness. Internal consistency for the present study was acceptable for survivors (a = 0.73) and spouses (a = 0.79). © 2015 John Wiley & Sons Ltd
Correspondence among prostate cancer couples
Cancer-related distress The IES (Horowitz et al. 1979) assessed psychological distress related to the prostate cancer. The IES is a 22-item self-report measure focusing on intrusive thoughts, avoidance behaviours, and hyperarousal symptoms associated with a stressor, in this case prostate cancer. Sample items include, ‘I thought about it when I didn’t mean to’ and ‘I tried to remove it from my memory’. Participants rated how true each statement was for them during the past week using a 6-point Likert scales (0 = Not at all; 5 = Often). Scores range from 0 to 110. The measure was completed at the time of the baseline survey. The scale has been widely used as a measure of cancer distress (Baider et al. 2003). Internal consistency for the present study was acceptable for survivors (a = 0.92) and spouses (a = 0.94). Analysis plan To address the first aim, we utilised dichotomous variables indicating whether each partner met recommended guidelines for fruit/vegetable consumption and physical activity. As previously described, couples were labelled as positively concordant, negatively concordant or discordant. There were nine couples in which one partner did not have complete data for the fruit/vegetable measure and seven couples in which one partner did not have complete data for the physical activity measure. Correspondence was only computed for couples with complete data for fruit/vegetable guidelines (n = 123) and physical activity guidelines (n = 125). The overall proportion of correspondence was calculated and Cohen’s Kappa was utilised to determine whether the level of similarity was larger than what would be expected to occur by chance. To address the second aim, chi-squared analyses were conducted to examine differences in concordance patterns for both fruit/vegetable guidelines and physical activity guidelines as a function of possible covariates, which included survivor race, couples’ employment status (both working, one partner working, or neither partner working), and type of treatment (surgery vs. radiation). Analysis of variance analyses were conducted to examine mean differences between the three groups (i.e. positively concordant, negatively concordant, discordant) on demographic (survivor age, survivor education, spouse age, spouse education, household income, length of relationship), medical (stage of cancer, time from diagnosis, Gleason score), and relationship (survivor relationship satisfaction, spouse relationship satisfaction, survivor-rated support for spouse’s engagement in © 2015 John Wiley & Sons Ltd
healthy diet and regular physical activity, spouse-rated support for patient’s engagement in healthy diet and physical activity) factors, as well as level of cancerrelated distress. RESULTS Participant characteristics The sample consisted of 132 couples. The mean age was 61 years for survivors and 57 years for spouses. The majority of survivors was White (78%) and had completed college or graduate school (68%). The majority of spouses was White (76%) and had completed at least some college education (61%). Most couples were married (96%). In approximately half of the couples, both partners were working part or full time (54%). There were two same-sex couples in the sample. The mean length of the couples’ relationship was 27 years. The average time since the prostate cancer diagnosis was 10 months (range = 2– 26 months). The complete characteristics of the sample are presented in Table 1. In total, 68% (n = 174/255) of the entire sample met fruit/vegetable guidelines and 56% (n = 143/256) met physical activity guidelines. Among survivors, 72% (n = 92/127) met the fruit/vegetable guidelines and 60% (n = 78/129) met physical activity guidelines. Among spouses, 64% (n = 82/128) met the fruit/vegetable guidelines and 51% (n = 65/127) met physical activity guidelines. Logistic regressions were utilised to examine individual-level and relationship-level factors associated with whether a survivor or spouse met fruit/vegetable or physical activity guidelines. Among survivors, meeting fruit/vegetables guidelines was associated with Caucasian race [Wald v2(1) = 6.72, P = 0.01, odds ratio = 10.57, 95% CI 1.78–62.83] and greater spouse-reported partner support [Wald v2(1) = 5.59, P = 0.018, odds ratio = 0.59, 95% CI 0.38–0.91]. Meeting physical activity guidelines was associated with greater time from diagnosis [Wald v2(1) = 4.41, P = 0.036, odds ratio = 1.19, 95% CI 1.01–1.41], greater survivor-reported partner support [Wald v2(1) = 5.02, P = 0.025, odds ratio = 1.47, 95% CI 1.05–2.07], and greater spouse-reported partner support [Wald v2(1) = 4.24, P = 0.04, odds ratio = 1.38, 95% CI 1.02–1.86]. Among spouses, meeting fruit/vegetable guidelines for spouses was not associated with any individual-level or relationship-level factors, but meeting physical activity guidelines was associated with greater survivor-reported cancer distress [Wald v2(1) = 7.71, P = 0.005, odds ratio = 1.05, 95% CI 1.02–1.09]. Descriptive analyses of survivors, spouses, and total sample in terms of physical activity and fruit and vegetable guidelines are presented in Table 2. 831
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Table 1. Characteristics of study sample Variable Age (years) Race White/Caucasian Black/African-American Asian Hispanic/Latino Other Education
