J Nutr Health Aging Volume 19, Number 2, 2015
PSYCHOSOCIAL MEDIATORS BETWEEN SOCIOECONOMIC STATUS AND DIETARY HABITS AMONG JAPANESE OLDER ADULTS H. SUGISAWA1, T. NOMURA2, M. TOMONAGA2 1. Graduate School of Gerontology, J.F. Oberlin University, Machida-shi, Tokyo, Japan; 2. College of Health and Welfare, J.F. Oberlin University, Machida-shi, Tokyo 194-0294 Japan. Corresponding author: Hidehiro Sugisawa, Graduate School of Gerontology, J. F. Oberlin University, 3758 Tokiwa-machi, Machida-shi, Tokyo, Japan, TEL: +81 (0) 42-797-9847, FAX: +81 (0) 42-797-9847, E-mail: [email protected]
Abstract: Introduction: Objectives: The purpose of this study was to examine psychosocial mediators between socioeconomic status (SES) and eating habits in older Japanese adults. Subjects and methods: A questionnaire was mailed to a representative sample of people who were 60 years and older (N=1,000) living in a suburban area within the Tokyo city metropolitan limits, in Japan. There were 552 effective participants in the study. Design: Dietary habits were evaluated by assessing the diversity of food that was consumed. SES was evaluated by educational attainment and household income. Four dimensions of psychosocial mediators were assessed: control expectancy, self-efficacy, social influence, and social support. Indirect effects of SES through the mediators were evaluated by using a multiple mediator model. Results: The relationship between education and dietary habits was mediated by three variables excluding social support. Especially, social influence had the strongest mediating effect. These three significant variables explained the majority of differences in dietary habits resulting from education. The effects of household income were also similarly mediated by the identical variables. Conclusions: Control expectancy, self-efficacy, and social influence mediate the relationship between SES and dietary habits. Key words: Mediators, socioeconomic status, dietary habits, Japanese older adults.
Introduction Research, in developing as well as developed countries has revealed socioeconomic differences in mortality and other health status indicators (1-4). Differences in health resulting from differences in socioeconomic status (SES) have been observed in adolescence, middle age and old age (5), although it is yet unknown whether such differences increase or decrease with age. In addition, in the adult population, SESdisadvantaged groups tend to exhibit poor dietary habits and food intake (6-8). Knowledge about the relationship between SES and dietary habits among older adults is relatively limited. However, several studies have shown that SES-disadvantaged older adults are at higher risk for unhealthy dietary habits (9-15). It has been suggested that the diets of SES-disadvantaged groups contribute to their poor health status (16, 17). Empirical studies provide evidence that dietary habits and food intake function as moderate mediators of SES differences in health. For example, Dollman et al. (18) found that in 6th year elementary school students, the negative relationships between SES and waist girth were mediated by fat intake. According to Panagiotakos et al. (19), the inverse relationships observed between SES and the prevalence of risk factors for cardiovascular disease was mainly explained by dietary habits. Although additional empirical studies are needed to determine whether or not dietary habits mediate the relationships between SES and health, it is likely that dietary habits function as mediators of SES differences in health in old age. On the other hand, only a few studies have examined the reasons for differences in dietary habits caused by SES. There Received March 17, 2014 Accepted for publication April 24, 2014
130
is evidence that psychological factors, such as knowledge and beliefs about nutrition influence food intake and food habits in old age (20-23), and that these factors are differentially distributed across SES groups (24). These findings suggest that low SES contributes to poor dietary habits through psychosocial mediators. Several studies have examined mediators of the relationships between SES and dietary habits. Ball et al. (25) examined the effects of adjustment to a wide range of mediators (cognitive and social factors of self-efficacy, belief of effect, social influence, social support, and food availability) in the association between maternal education and food intake indicators among adolescents. They demonstrated that these cognitive and social factors played an important role in mediating social variations in food intake indicators. Most other studies that have investigated psychosocial factors as mediators have been limited in scope, measuring only partial and narrowly focused aspects of these factors (26-31). In addition, few studies have focused on the role of social factors as mediators (32). Social factors, such as social influence, social control, and social support, can encourage healthy behaviors (33). Distributions of such social factors also differ according to SES (34). A second limitation of previous research is that psychosocial factors have been measured by using general scales, rather than by specific psychosocial scales that correspond to dietary habits. As a result, effects of psychosocial factors as mediators may have been underestimated in previous studies. Self-efficacy (SE) is an important psychosocial factor that is situation-specific and tends to vary considerably across domains of function. Therefore, Bandura has strongly recommended that SE be measured specifically in relation to
J Nutr Health Aging Volume 19, Number 2, 2015
JNHA: NUTRITION the behavior of interest (35). Finally, little research has focused explicitly on old age. Most previous studies on the role of psychosocial factors in mediating SES differences in dietary habits have examined only younger age groups. It is unclear whether or not findings obtained from research on young age groups may generalize to older groups. Therefore, the goal of this study was to examine mediating effects of psychosocial factors (control expectancy, self-efficacy, social influence, and social support) between SES and dietary habits among older adults. Analytical framework Figure 1 shows the analytical framework of this study, which selected psychosocial factors based on several theoretical viewpoints. SES differences in dietary habits can be explained on the basis of psychosocial factors according to the analytic framework proposed by Leganger and Kraft (26) and Ball et al. (25). Leganger and Kraft (26) focused on control perception as a psychosocial factor. Control perception takes the form of two different constructs: control expectancy and self-efficacy. Control expectancy is expressed as response expectancy in protection motivation theory and as outcome expectancy in the theory of planned behavior (26). The concept of self-efficacy proposed by Bandura (36), is similar to perceived behavioral control in the theory of planned behavior (26). Figure1 Analytic framework
some evidence that these social factors may mediate between SES and dietary habits. For example, Toner et al. (38) and Van Duyn et al. (39) reported that social support for eating influenced eating habits, and Inglis et al. (40) found that SESdisadvantaged people reported lower levels of social support. In general, education, occupation, and income have been employed to measure SES (41). However, occupation is not an effective indicator for measuring SES, because in Japan, a majority of older adults do not enter the work force. The rate of participation of people aged 60 years and older in the Japanese labor force was 29.2 % in 2011 (42). Moreover, some researchers have suggested that occupational status is a problematic indicator of socioeconomic status among older adults (14, 15). Therefore, in this study, only education and income were employed as measures of SES. Methods Participants One thousand participants were selected by systematic sampling of residents aged 60 years and older living in the Tokyo metropolitan area. Self-administered questionnaires were sent to them by mail in January 2012. Reminder letters were sent just after the time limit for returning the questionnaires expired. The number of questionnaires returned was 579. The questionnaire included an item that inquired, “who responded to the questionnaires.” The questionnaires that were not answered by eligible persons were excluded (N=27). The final number of participants whose data were analyzed was 552. Assessments Demographic variables Gender (1 = male, 0 = female), age, and the number of people living in the household were assessed. Education Participants were asked to indicate their highest academic qualification from the following list: “junior high school graduate,” “high school graduate,” “vocational school graduate,” “ junior college graduate,” or “university graduate, or above.” The numbers 6, 9, 10, 11, 13 were assigned to each category to quantify the responses.
Education and household income are hypothesized to exert an indirect effect on eating habits through control expectancy, self-efficacy, social influence, and social support
In addition, based on the study of Ball et al (25), SES differences in diet can be explained from social factors, especially social influence and social support. Major concepts in social cognitive theory include environmental and observational learning as socially determinant factors (37). Social relations are relevant in different phases of the onset and continuation of health behavior, where functions include motivation, normative expectations, emotional and practical support, and affirmation. Empirical studies provide 131
Household income Annual household income was assessed by measuring the total annual household income. Participants were asked to indicate the approximate total annual income of all the members of their household from all sources of income before tax deductions in the previous year. Choices were composed of eleven levels. The midpoint of each category was used for quantification. For example, the categories, “more than 2 and less than 3 million yen,” and “more than 7.5 and less than 10 million yen” were assigned 2.5 and 8.25 million yen respectively. The midpoint of each category was divided by the
J Nutr Health Aging Volume 19, Number 2, 2015
PSYCHOSOCIAL MEDIATORS BETWEEN SOCIOECONOMIC STATUS AND DIETARY HABITS square root of the number of people living in the household to adjust for the influence of household size on income. Control expectancy (CE) This variable is composed of three items that was assessed by the scale developed by Leganger and Kraft (26). The scale inquires participants to indicate the importance of eating the following foods on a daily basis for maintaining their health: (a) vegetables and fruits; (b) milk, dairy products, and soybean products; (c) meats and seafood. Responses are scored on a four-point scale, ranging from 1 (not so important) to 4 (very important). Principal components analysis extracted a single component by using an eigenvalue >1.0 criterion, which explained 71.8% of the total variance in the three items. Cronbach’s alpha of this index is 0.84. Self-efficacy (SE) This variable is composed of three items that was assessed by the scale developed by Leganger and Kraft (26). Participants are asked questions about their confidence that they would eat the following food every day during the next four weeks, even if they did not have an appetite: (a) vegetables and fruits; (b) milk, dairy products, and soybean products; (c) meats and seafood. Responses are scored on a four-point scale, ranging from 1 (not at all confident) to 4 (very confident). Principal components analysis extracted a single component by imposing an eigenvalue >1.0 criterion, which explained 75.3% of the total variance in the three items. Cronbach’s alpha of this index is 0.79. Social influence (SI) This variable is composed of three items. The participants were asked if their family or relatives eat the following foods almost every day: (a) vegetables and fruits; (b) milk, dairy products, and soybean products; (c) meats and seafood. The participants provided a rating of frequencies: almost every day (coded 4), sometimes (coded 3), rarely (coded 2), never (coded 1). These items were developed based on the scale of Ball et al (25). Principal components analysis extracted a single component by imposing an eigenvalue >1.0 criterion, which explained 57.2% of the total variance in the three items. Cronbach’s alpha for this scale is 0.61. Social support by surrounding people (SS) This variable was composed of four items based on the scale developed by Leganger and Kraft (26). The participants were asked about the level of perceived social support they received from their family/friends in each of the following scenarios: (a) to encourage them to eat a well-balanced diet if they don’t eat such a diet, (b) to help them prepare a meal if they can’t do it, (c) to warn them about eating salty food if they eat too much of it, and (d) to offer advice if they need to change their dietary habits. Responses are scored on a four-point scale, ranging from 1 (not supportive or no support) to 4 (very supportive). Responses were summed to provide one efficacy score.
Principal components analysis extracted a single component by imposing an eigenvalue >1.0 criterion. This component explained 75.7% of the total variance in the four items, which all loaded above 0.8 on this component. Cronbach’s alpha for this index is 0.89. Eating habits A number of studies have assessed food intake of individual fruit or vegetables. However, this study assessed dietary habits by using the dietary variety index developed by Kumagai et al (43). This index counts the number of 10 food groups consumed daily as reported on a food frequency questionnaire: meat, fish and shellfish, seaweed, green or yellow vegetables, milk, soybean products, potatoes fat and oil, fruits, and egg. Participants made a choice between “eat almost every day” and “eat less often than every day”. These options were scored 1 and 0, respectively. Scores on the 10 items were summed to provide the dietary variety index. Although the index has not been used internationally, it has high predictive validity in predicting the functional capacity among older Japanese adults. The dietary variety index includes many elements that make up a healthy dietary pattern (44). Statistical Method This study examined whether or not certain mediators could explain the relationships between SES and dietary habits. Mplus ver.5 (45) was used for data analysis. Multiple mediation analysis proposed by Preacher and Hayes (46) was used, facilitating the estimation of total and specific indirect effects in a multiple model. In addition, we examined the null hypotheses that indirect effects of each of the four mediators resulting from each education and income category were equal (46). All variables in the model were standardized to compare the sizes of the indirect effects among each mediator. Bootstrapping was used to estimate the total and specific indirect effects of the mediators. Point estimates and 95% percentile confidence interval were determined according to the null hypothesis. Full Information Maximum Likelihood (FIML) approach to handling missing data was employed in the analysis (45). We examined whether or not there were mediation effects, even if the total effect of the independent variable (e.g. education) did not have a significant effect on the dependent variable (e.g. dietary habits), based on the suggestion that the significant effect of the independent variable was not always necessary for mediations to occur (46). If M1 acts as a mediator and a second mediator, M2, acts as a suppressor, the total effects of the independent variable on the dependent variable might be reduced, because of the possibility that indirect effects of M1 and M2 cancel each other. Ethical considerations A leading research company collected the data for this study. This company’s measures for protecting personal information have been approved by the Japan Institute for 132
J Nutr Health Aging Volume 19, Number 2, 2015
JNHA: NUTRITION Promotion of Digital Economy and Community. This study was conducted according to the guidelines laid down in the Helsinki Declaration. Moreover, all the procedures of the study were approved by the Research Ethics Board of J. F. Oberlin University. A letter of invitation explaining the content of the study and the questionnaire was sent to each potential participant in this survey. Data collection procedures assured confidentiality by the use of self-administered, anonymous questionnaires. Participation in this study was completely voluntary, and confidentiality was fully guaranteed. Only respondents who wished to participate in this survey sent back their questionnaires to us. Results Descriptive statistics Table 1 shows descriptive statistics and correlations among participants’ variables. It can be seen that neither socioeconomic indices were significantly related to dietary habits, although there was a significant impact of education on dietary habits after controlling for age and sex. All correlations among the variables were less than .5 and there was no Multicollinearity among the variables. The path coefficient of educational attainment (=0.12, P =.01) was significant, however, the path coefficient of income after entering gender and age as control variable was not significant (=0.07, P >.10). Multiple mediation Table 2 shows the results of multiple mediation analysis. Goodness of fit of this model was enough (CFI was .96 and SRMR was .03). All direct effects of both education and income on each mediator were significant. Moreover, nearly all the direct effects of each mediator on dietary habits were significant. However, contrary to the effects of other mediators, only social support had a direct, negative effect on dietary habits. Multiple mediation analysis showed that both education and income had significant total indirect effects on dietary habits. In addition, the direct effects of both education and
income on dietary habits, after reducing indirect effects were much smaller and were not significant (each path coefficient of education and income was -.01 and .00). Bootstrap estimate showed that CE, SE, and SI were significant specific mediators of the relationships between education and income with dietary habits. The path coefficient size of SI was largest among the path coefficient sizes of mediators. However, the result of testing the alternative hypothesis indicated that the indirect effect of SS on education and income was significantly lower than the indirect effects of other mediators. Discussion In Japan, SES differences in health have been observed over a wide age range (47, 48). Few studies have also shown SES differences in dietary habits (49, 50). However, little information is available about SES differences in dietary habits among older adults. Studies examining SES differences in dietary habits and food intake have typically used a single source of nutrition or food to measure dietary habits and food intake. These studies have reported diverse findings about SES differences based on different food and nutrition indicators (32, 51). The present study used a comprehensive measure of dietary habits to examine SES differences. The results confirmed earlier studies in Western countries (9-14) and indicated that SES-disadvantaged older adults in Japan, also had poorer dietary habits than more advantaged peers. Thus, a population-wide approach did not alter the findings regarding the underlying differences in SES related to dietary habits observed in other countries. Based on this finding, it is suggested that efforts to improve unhealthy dietary habits in SES-disadvantaged older adults need to be complemented by policies targeted particularly for this group (26). Studies by Leganger and Kraft (26) and Turrell and Kavanagh (27) examined the mediating effects of psychological factors and did not focus on social factors as mediators. On the other hand, the study by Lindstrom et al. (32) examined
Table 1 Descriptive statistics and correlations among the variables Variables
Means
Standard Deviation
1.age 71.46 2.Gender 0.40 3.Education 9.92 4.Equivalised income(yen) 3370376.08 5.CE 10.26 6.SE 8.68 7.SI 11.19 8.SS 12.92 9.Dietary Habits 5.19
7.85 0.49 2.16 2268426.10 1.55 1.86 1.12 3.12 2.50
1
2
3
4
5
6
7
8
-.10** -.14** -.12* .13** .03 .15** .06 .08
.29** .03 -.17** .03 -.12** .10* -.14**
.21** .12** .13** .08 .09* .07
.14** .11* .11* .18** .09
.33** .36** .17** .37**
.20** .14** .38**
.26** .48**
.08
CE, control expectancy; SE, self efficacy; SI, social influence; SS, social support; Correlations were calculated by exclusion of case pair-wise; *P
PSYCHOSOCIAL MEDIATORS BETWEEN SOCIOECONOMIC STATUS AND DIETARY HABITS AMONG JAPANESE OLDER ADULTS H. SUGISAWA1, T. NOMURA2, M. TOMONAGA2 1. Graduate School of Gerontology, J.F. Oberlin University, Machida-shi, Tokyo, Japan; 2. College of Health and Welfare, J.F. Oberlin University, Machida-shi, Tokyo 194-0294 Japan. Corresponding author: Hidehiro Sugisawa, Graduate School of Gerontology, J. F. Oberlin University, 3758 Tokiwa-machi, Machida-shi, Tokyo, Japan, TEL: +81 (0) 42-797-9847, FAX: +81 (0) 42-797-9847, E-mail: [email protected]
Abstract: Introduction: Objectives: The purpose of this study was to examine psychosocial mediators between socioeconomic status (SES) and eating habits in older Japanese adults. Subjects and methods: A questionnaire was mailed to a representative sample of people who were 60 years and older (N=1,000) living in a suburban area within the Tokyo city metropolitan limits, in Japan. There were 552 effective participants in the study. Design: Dietary habits were evaluated by assessing the diversity of food that was consumed. SES was evaluated by educational attainment and household income. Four dimensions of psychosocial mediators were assessed: control expectancy, self-efficacy, social influence, and social support. Indirect effects of SES through the mediators were evaluated by using a multiple mediator model. Results: The relationship between education and dietary habits was mediated by three variables excluding social support. Especially, social influence had the strongest mediating effect. These three significant variables explained the majority of differences in dietary habits resulting from education. The effects of household income were also similarly mediated by the identical variables. Conclusions: Control expectancy, self-efficacy, and social influence mediate the relationship between SES and dietary habits. Key words: Mediators, socioeconomic status, dietary habits, Japanese older adults.
Introduction Research, in developing as well as developed countries has revealed socioeconomic differences in mortality and other health status indicators (1-4). Differences in health resulting from differences in socioeconomic status (SES) have been observed in adolescence, middle age and old age (5), although it is yet unknown whether such differences increase or decrease with age. In addition, in the adult population, SESdisadvantaged groups tend to exhibit poor dietary habits and food intake (6-8). Knowledge about the relationship between SES and dietary habits among older adults is relatively limited. However, several studies have shown that SES-disadvantaged older adults are at higher risk for unhealthy dietary habits (9-15). It has been suggested that the diets of SES-disadvantaged groups contribute to their poor health status (16, 17). Empirical studies provide evidence that dietary habits and food intake function as moderate mediators of SES differences in health. For example, Dollman et al. (18) found that in 6th year elementary school students, the negative relationships between SES and waist girth were mediated by fat intake. According to Panagiotakos et al. (19), the inverse relationships observed between SES and the prevalence of risk factors for cardiovascular disease was mainly explained by dietary habits. Although additional empirical studies are needed to determine whether or not dietary habits mediate the relationships between SES and health, it is likely that dietary habits function as mediators of SES differences in health in old age. On the other hand, only a few studies have examined the reasons for differences in dietary habits caused by SES. There Received March 17, 2014 Accepted for publication April 24, 2014
130
is evidence that psychological factors, such as knowledge and beliefs about nutrition influence food intake and food habits in old age (20-23), and that these factors are differentially distributed across SES groups (24). These findings suggest that low SES contributes to poor dietary habits through psychosocial mediators. Several studies have examined mediators of the relationships between SES and dietary habits. Ball et al. (25) examined the effects of adjustment to a wide range of mediators (cognitive and social factors of self-efficacy, belief of effect, social influence, social support, and food availability) in the association between maternal education and food intake indicators among adolescents. They demonstrated that these cognitive and social factors played an important role in mediating social variations in food intake indicators. Most other studies that have investigated psychosocial factors as mediators have been limited in scope, measuring only partial and narrowly focused aspects of these factors (26-31). In addition, few studies have focused on the role of social factors as mediators (32). Social factors, such as social influence, social control, and social support, can encourage healthy behaviors (33). Distributions of such social factors also differ according to SES (34). A second limitation of previous research is that psychosocial factors have been measured by using general scales, rather than by specific psychosocial scales that correspond to dietary habits. As a result, effects of psychosocial factors as mediators may have been underestimated in previous studies. Self-efficacy (SE) is an important psychosocial factor that is situation-specific and tends to vary considerably across domains of function. Therefore, Bandura has strongly recommended that SE be measured specifically in relation to
J Nutr Health Aging Volume 19, Number 2, 2015
JNHA: NUTRITION the behavior of interest (35). Finally, little research has focused explicitly on old age. Most previous studies on the role of psychosocial factors in mediating SES differences in dietary habits have examined only younger age groups. It is unclear whether or not findings obtained from research on young age groups may generalize to older groups. Therefore, the goal of this study was to examine mediating effects of psychosocial factors (control expectancy, self-efficacy, social influence, and social support) between SES and dietary habits among older adults. Analytical framework Figure 1 shows the analytical framework of this study, which selected psychosocial factors based on several theoretical viewpoints. SES differences in dietary habits can be explained on the basis of psychosocial factors according to the analytic framework proposed by Leganger and Kraft (26) and Ball et al. (25). Leganger and Kraft (26) focused on control perception as a psychosocial factor. Control perception takes the form of two different constructs: control expectancy and self-efficacy. Control expectancy is expressed as response expectancy in protection motivation theory and as outcome expectancy in the theory of planned behavior (26). The concept of self-efficacy proposed by Bandura (36), is similar to perceived behavioral control in the theory of planned behavior (26). Figure1 Analytic framework
some evidence that these social factors may mediate between SES and dietary habits. For example, Toner et al. (38) and Van Duyn et al. (39) reported that social support for eating influenced eating habits, and Inglis et al. (40) found that SESdisadvantaged people reported lower levels of social support. In general, education, occupation, and income have been employed to measure SES (41). However, occupation is not an effective indicator for measuring SES, because in Japan, a majority of older adults do not enter the work force. The rate of participation of people aged 60 years and older in the Japanese labor force was 29.2 % in 2011 (42). Moreover, some researchers have suggested that occupational status is a problematic indicator of socioeconomic status among older adults (14, 15). Therefore, in this study, only education and income were employed as measures of SES. Methods Participants One thousand participants were selected by systematic sampling of residents aged 60 years and older living in the Tokyo metropolitan area. Self-administered questionnaires were sent to them by mail in January 2012. Reminder letters were sent just after the time limit for returning the questionnaires expired. The number of questionnaires returned was 579. The questionnaire included an item that inquired, “who responded to the questionnaires.” The questionnaires that were not answered by eligible persons were excluded (N=27). The final number of participants whose data were analyzed was 552. Assessments Demographic variables Gender (1 = male, 0 = female), age, and the number of people living in the household were assessed. Education Participants were asked to indicate their highest academic qualification from the following list: “junior high school graduate,” “high school graduate,” “vocational school graduate,” “ junior college graduate,” or “university graduate, or above.” The numbers 6, 9, 10, 11, 13 were assigned to each category to quantify the responses.
Education and household income are hypothesized to exert an indirect effect on eating habits through control expectancy, self-efficacy, social influence, and social support
In addition, based on the study of Ball et al (25), SES differences in diet can be explained from social factors, especially social influence and social support. Major concepts in social cognitive theory include environmental and observational learning as socially determinant factors (37). Social relations are relevant in different phases of the onset and continuation of health behavior, where functions include motivation, normative expectations, emotional and practical support, and affirmation. Empirical studies provide 131
Household income Annual household income was assessed by measuring the total annual household income. Participants were asked to indicate the approximate total annual income of all the members of their household from all sources of income before tax deductions in the previous year. Choices were composed of eleven levels. The midpoint of each category was used for quantification. For example, the categories, “more than 2 and less than 3 million yen,” and “more than 7.5 and less than 10 million yen” were assigned 2.5 and 8.25 million yen respectively. The midpoint of each category was divided by the
J Nutr Health Aging Volume 19, Number 2, 2015
PSYCHOSOCIAL MEDIATORS BETWEEN SOCIOECONOMIC STATUS AND DIETARY HABITS square root of the number of people living in the household to adjust for the influence of household size on income. Control expectancy (CE) This variable is composed of three items that was assessed by the scale developed by Leganger and Kraft (26). The scale inquires participants to indicate the importance of eating the following foods on a daily basis for maintaining their health: (a) vegetables and fruits; (b) milk, dairy products, and soybean products; (c) meats and seafood. Responses are scored on a four-point scale, ranging from 1 (not so important) to 4 (very important). Principal components analysis extracted a single component by using an eigenvalue >1.0 criterion, which explained 71.8% of the total variance in the three items. Cronbach’s alpha of this index is 0.84. Self-efficacy (SE) This variable is composed of three items that was assessed by the scale developed by Leganger and Kraft (26). Participants are asked questions about their confidence that they would eat the following food every day during the next four weeks, even if they did not have an appetite: (a) vegetables and fruits; (b) milk, dairy products, and soybean products; (c) meats and seafood. Responses are scored on a four-point scale, ranging from 1 (not at all confident) to 4 (very confident). Principal components analysis extracted a single component by imposing an eigenvalue >1.0 criterion, which explained 75.3% of the total variance in the three items. Cronbach’s alpha of this index is 0.79. Social influence (SI) This variable is composed of three items. The participants were asked if their family or relatives eat the following foods almost every day: (a) vegetables and fruits; (b) milk, dairy products, and soybean products; (c) meats and seafood. The participants provided a rating of frequencies: almost every day (coded 4), sometimes (coded 3), rarely (coded 2), never (coded 1). These items were developed based on the scale of Ball et al (25). Principal components analysis extracted a single component by imposing an eigenvalue >1.0 criterion, which explained 57.2% of the total variance in the three items. Cronbach’s alpha for this scale is 0.61. Social support by surrounding people (SS) This variable was composed of four items based on the scale developed by Leganger and Kraft (26). The participants were asked about the level of perceived social support they received from their family/friends in each of the following scenarios: (a) to encourage them to eat a well-balanced diet if they don’t eat such a diet, (b) to help them prepare a meal if they can’t do it, (c) to warn them about eating salty food if they eat too much of it, and (d) to offer advice if they need to change their dietary habits. Responses are scored on a four-point scale, ranging from 1 (not supportive or no support) to 4 (very supportive). Responses were summed to provide one efficacy score.
Principal components analysis extracted a single component by imposing an eigenvalue >1.0 criterion. This component explained 75.7% of the total variance in the four items, which all loaded above 0.8 on this component. Cronbach’s alpha for this index is 0.89. Eating habits A number of studies have assessed food intake of individual fruit or vegetables. However, this study assessed dietary habits by using the dietary variety index developed by Kumagai et al (43). This index counts the number of 10 food groups consumed daily as reported on a food frequency questionnaire: meat, fish and shellfish, seaweed, green or yellow vegetables, milk, soybean products, potatoes fat and oil, fruits, and egg. Participants made a choice between “eat almost every day” and “eat less often than every day”. These options were scored 1 and 0, respectively. Scores on the 10 items were summed to provide the dietary variety index. Although the index has not been used internationally, it has high predictive validity in predicting the functional capacity among older Japanese adults. The dietary variety index includes many elements that make up a healthy dietary pattern (44). Statistical Method This study examined whether or not certain mediators could explain the relationships between SES and dietary habits. Mplus ver.5 (45) was used for data analysis. Multiple mediation analysis proposed by Preacher and Hayes (46) was used, facilitating the estimation of total and specific indirect effects in a multiple model. In addition, we examined the null hypotheses that indirect effects of each of the four mediators resulting from each education and income category were equal (46). All variables in the model were standardized to compare the sizes of the indirect effects among each mediator. Bootstrapping was used to estimate the total and specific indirect effects of the mediators. Point estimates and 95% percentile confidence interval were determined according to the null hypothesis. Full Information Maximum Likelihood (FIML) approach to handling missing data was employed in the analysis (45). We examined whether or not there were mediation effects, even if the total effect of the independent variable (e.g. education) did not have a significant effect on the dependent variable (e.g. dietary habits), based on the suggestion that the significant effect of the independent variable was not always necessary for mediations to occur (46). If M1 acts as a mediator and a second mediator, M2, acts as a suppressor, the total effects of the independent variable on the dependent variable might be reduced, because of the possibility that indirect effects of M1 and M2 cancel each other. Ethical considerations A leading research company collected the data for this study. This company’s measures for protecting personal information have been approved by the Japan Institute for 132
J Nutr Health Aging Volume 19, Number 2, 2015
JNHA: NUTRITION Promotion of Digital Economy and Community. This study was conducted according to the guidelines laid down in the Helsinki Declaration. Moreover, all the procedures of the study were approved by the Research Ethics Board of J. F. Oberlin University. A letter of invitation explaining the content of the study and the questionnaire was sent to each potential participant in this survey. Data collection procedures assured confidentiality by the use of self-administered, anonymous questionnaires. Participation in this study was completely voluntary, and confidentiality was fully guaranteed. Only respondents who wished to participate in this survey sent back their questionnaires to us. Results Descriptive statistics Table 1 shows descriptive statistics and correlations among participants’ variables. It can be seen that neither socioeconomic indices were significantly related to dietary habits, although there was a significant impact of education on dietary habits after controlling for age and sex. All correlations among the variables were less than .5 and there was no Multicollinearity among the variables. The path coefficient of educational attainment (=0.12, P =.01) was significant, however, the path coefficient of income after entering gender and age as control variable was not significant (=0.07, P >.10). Multiple mediation Table 2 shows the results of multiple mediation analysis. Goodness of fit of this model was enough (CFI was .96 and SRMR was .03). All direct effects of both education and income on each mediator were significant. Moreover, nearly all the direct effects of each mediator on dietary habits were significant. However, contrary to the effects of other mediators, only social support had a direct, negative effect on dietary habits. Multiple mediation analysis showed that both education and income had significant total indirect effects on dietary habits. In addition, the direct effects of both education and
income on dietary habits, after reducing indirect effects were much smaller and were not significant (each path coefficient of education and income was -.01 and .00). Bootstrap estimate showed that CE, SE, and SI were significant specific mediators of the relationships between education and income with dietary habits. The path coefficient size of SI was largest among the path coefficient sizes of mediators. However, the result of testing the alternative hypothesis indicated that the indirect effect of SS on education and income was significantly lower than the indirect effects of other mediators. Discussion In Japan, SES differences in health have been observed over a wide age range (47, 48). Few studies have also shown SES differences in dietary habits (49, 50). However, little information is available about SES differences in dietary habits among older adults. Studies examining SES differences in dietary habits and food intake have typically used a single source of nutrition or food to measure dietary habits and food intake. These studies have reported diverse findings about SES differences based on different food and nutrition indicators (32, 51). The present study used a comprehensive measure of dietary habits to examine SES differences. The results confirmed earlier studies in Western countries (9-14) and indicated that SES-disadvantaged older adults in Japan, also had poorer dietary habits than more advantaged peers. Thus, a population-wide approach did not alter the findings regarding the underlying differences in SES related to dietary habits observed in other countries. Based on this finding, it is suggested that efforts to improve unhealthy dietary habits in SES-disadvantaged older adults need to be complemented by policies targeted particularly for this group (26). Studies by Leganger and Kraft (26) and Turrell and Kavanagh (27) examined the mediating effects of psychological factors and did not focus on social factors as mediators. On the other hand, the study by Lindstrom et al. (32) examined
Table 1 Descriptive statistics and correlations among the variables Variables
Means
Standard Deviation
1.age 71.46 2.Gender 0.40 3.Education 9.92 4.Equivalised income(yen) 3370376.08 5.CE 10.26 6.SE 8.68 7.SI 11.19 8.SS 12.92 9.Dietary Habits 5.19
7.85 0.49 2.16 2268426.10 1.55 1.86 1.12 3.12 2.50
1
2
3
4
5
6
7
8
-.10** -.14** -.12* .13** .03 .15** .06 .08
.29** .03 -.17** .03 -.12** .10* -.14**
.21** .12** .13** .08 .09* .07
.14** .11* .11* .18** .09
.33** .36** .17** .37**
.20** .14** .38**
.26** .48**
.08
CE, control expectancy; SE, self efficacy; SI, social influence; SS, social support; Correlations were calculated by exclusion of case pair-wise; *P
