Annals of Epidemiology 25 (2015) 406e413
Contents lists available at ScienceDirect
Annals of Epidemiology journal homepage: www.annalsofepidemiology.org
Original article
Physical activity in relation to body size and composition in women in UK Biobank Wenji Guo BS *, Kathryn E. Bradbury PhD, Gillian K. Reeves PhD, Timothy J. Key PhD Cancer Epidemiology Unit, Nuffield Department of Population Health, University of Oxford, Oxford, UK
a r t i c l e i n f o
a b s t r a c t
Article history: Received 8 August 2014 Accepted 25 January 2015 Available online 4 February 2015
Purpose: Physical activity is thought to protect against obesity, but the evidence is limited and few large studies of this topic have direct, objective measures of several different anthropometric variables. We examined the association of self-reported physical activity with measures of total and central adiposity. Methods: Our cross-sectional study included 38,201 premenopausal and 94,592 postmenopausal healthy women aged 40 to 70 years in UK Biobank, recruited from 2006 to 2010. Results: Means for total and vigorous physical activity were 31.3 (SD, 30.8) and 9.7 (SD, 14.8) metabolic equivalent h/wk, respectively, for premenopausal and 34.4 (SD, 33.1) and 8.9 (SD, 15.6) metabolic equivalent h/wk, respectively, for postmenopausal women. Multiple linear regression models showed that in both premenopausal and postmenopausal women, body mass index, body fat mass and percentage, trunk fat mass and percentage, waist and hip circumference, and waist-to-hip ratio were lower in women with higher physical activity (P < .0001). Within each category of total physical activity, a larger proportion of vigorous physical activity was associated with lower adiposity (P < .0001). Conclusions: These findings support the roles of a physically active lifestyle and vigorous exercise in maintaining healthy body size and composition. Higher exercise intensity may be associated with lower adiposity, beyond the influence of exercise frequency and duration. Ó 2015 Elsevier Inc. All rights reserved.
Keywords: Adiposity Body fat percentage Body mass index Cross-sectional studies Intensity Menopause Physical activity
Introduction Obesity is of major, general public health concern because of its association with increased risk of a variety of diseases including diabetes, heart disease, hypertension, stroke, and certain cancers such as breast and endometrial [1]. Although physical activity is widely believed to be an important determinant of body size and composition, the full nature of the relationship is still unclear [2,3]. Although observational studies support an association between exercise and weight-loss maintenance, randomized controlled trials have produced inconsistent results [4]. Questions also remain over the role of vigorous compared with lower intensity physical activity in reducing adiposity and preventing weight gain, and over the relationship between physical activity and different measures of overall versus central adiposity [5,6]. Because risks for some obesity-related diseases such as breast cancer and cardiovascular disease differ by menopausal status, it is of particular interest to examine the associations between physical activity and adiposity
* Corresponding author. Cancer Epidemiology Unit, Nuffield Department of Population Health, University of Oxford, Richard Doll Building, Roosevelt Drive, Oxford OX3 7LF, UK. Tel.: þ44 (0) 1865 289 600; fax: þ44 (0) 1865 289 610. E-mail address: [email protected] (W. Guo). http://dx.doi.org/10.1016/j.annepidem.2015.01.015 1047-2797/Ó 2015 Elsevier Inc. All rights reserved.
separately according to menopausal status in women [7,8]. Some previous large studies have been limited by low numbers of women reporting vigorous physical activity [9]. A number of anthropometric variables have been reported and used in public health recommendations. Because an increase in particular indices of body size may have an effect on specific health outcomes, it is important to assess which indices are likely to be modified by behaviors such as exercise. We report here a crosssectional analysis of associations between reported levels of overall and of vigorous physical activity and several objective measures of body size and composition in more than 132,000 premenopausal and postmenopausal women. In particular, we assess the hypothesis that physical activity is related to body size and composition and that associations may vary by particular measures of adiposity. This research has been conducted using the UK Biobank resource, a nationwide study of approximately 500,000 UK adults. Methods Data source Data were obtained by application to UK Biobank (reference number 3248, approved in August 2013). Details of the rationale,
W. Guo et al. / Annals of Epidemiology 25 (2015) 406e413
design, and survey methods for UK Biobank have been described elsewhere [10], and information on data available and access procedures are given on the study Web site (http://www.ukbiobank.ac. uk/). UK Biobank has approval from the North West Multi-centre Research Ethics Committee, the National Information Governance Board for Health and Social Care in England and Wales, and the Community Health Index Advisory Group in Scotland. All participants provided written informed consent. Study participants The complete UK Biobank data set includes 502, 656 UK adults (229,182 men and 273,474 women) between 40 to 70 years of age at recruitment during 2006 to 2010. Because participation was voluntary and the data collection process rigorous, UK Biobank aimed to enhance generalizability rather than to be representative of the UK population. Participant recruitment was conducted via centrally coordinated identification and invitation from population-based National Health Service patient registers of individuals living within a reasonable distance of an assessment center. Participants completed a touchscreen questionnaire during the baseline assessment center visit that included questions on sociodemographics, lifestyle, health and medical history, and sex-specific factors. Menopausal status provided by UK Biobank was self-reported; for these analyses, women without self-reported menopausal status who were older than 53 years at recruitment and/or had had both ovaries removed were categorized as postmenopausal (n ¼ 29,777), and women younger than 45 years who had not undergone a bilateral oophorectomy were categorized as premenopausal (n ¼ 1053). Women were excluded from the analyses if they reported at recruitment a long-standing illness, disability, infirmity, or had unknown status for this variable (n ¼ 87,989), had unknown menopausal status (n ¼ 15,517), were pregnant (n ¼ 121), or had missing data on any of the physical activity variables used in our analyses (n ¼ 70,343). Participants were also excluded if the sum of all walking, moderate, and vigorous time variables was greater than 6720 min/wk as detailed in the International Physical Activity Questionnaire (IPAQ) scoring guidelines (n ¼ 2184), which can be accessed at https://sites.google.com/site/theipaq/scoring-protocol. Included in the analyses were 38,201 premenopausal and 94,592 postmenopausal women. Physical activity Physical activity questions asked on the baseline questionnaire captured the frequency and duration of three different levels of activity (walking, moderate, and vigorous). Participants were asked how many days per typical week they spent engaged in each category of activity. For each category in which an answer of one or more days was given, the participant was then asked the number of minutes spent on the activity during a typical day. Questions were adapted from the IPAQ short form, a validated survey instrument [11]. Questions are listed in Supplementary Table 1 and are available to view on the UK Biobank Web site (http://biobank.ctsu.ox.ac.uk/ crystal/). We used metabolic equivalents (METs) to quantify physical activity; 1 MET is expended by sitting quietly for 1 hour, and the MET value reflects the ratio of energy expended per kilogram of body weight per hour to that expended when sitting quietly [12]. The number of minutes per day engaged in each level of activity was multiplied by the respective MET score for that level of activity. MET minutes per day were converted to MET hours per week. The total amount of METs was calculated by summing total METs from each activity level. In line with IPAQ guidelines [11], physical activity of less than 10 min/d for walking, moderate, or vigorous activity was recoded to 0.
407
Each category was assigned the following MET hour values: 3.3 for walking, 4.0 for moderate physical activity, and 8.0 for vigorous physical activity [11]. Because individuals are estimated to expend 1 MET/h sitting quietly, we report physical activity as excess METs [13]. Excess METs were calculated by subtracting one from the MET value multiplier for each category, giving values of 2.3 for walking, 3.0 for moderate physical activity, and 7.0 for vigorous physical activity. To assess the importance of vigorous physical activity relative to total physical activity, vigorous physical activity was divided by total physical activity to generate a ratio of vigorous-to-total physical activity. The median ratio of vigorous-to-total physical activity in participants who engaged in any vigorous physical activity was 33%. For analysis, participants were grouped into three categories of vigorous-to-total physical activity: zero percent vigorous physical activity, less than 33% vigorous physical activity, and more than 33% vigorous physical activity. Anthropometry and body composition At the UK Biobank baseline interview, trained staff used standard procedures to measure and record standing height using the Seca 202 device (Seca, Hamburg, Germany). The Wessex non-stretchable sprung tape (Wessex, United Kingdom) measure was used to measure waist and hip circumference. The Tanita BC-418MA body composition analyzer (Tanita, Tokyo, Japan) was used to assess bioimpedance measures including body fat percentage, whole body fat mass, trunk fat percentage, and trunk fat mass. UK Biobank derived body mass index (BMI) by dividing weight (kilogram) by the square of standing height (square meter). We derived waist-to-hip ratio (WHR) by dividing waist circumference by hip circumference. Statistical analyses Multiple linear regression models were used to examine the association between physical activity and the various anthropometric and body composition measures. Amount of physical activity was categorized into nine groups to obtain an approximately even distribution of participants (0,1e4.9, 5e9.9,10e14.9,15e24.9, 25e34.9, 35e49.9, 50e74.9, and 75 excess MET-h/wk) and the figures show the mean within each category. Those who did no physical activity were placed in a separate category even though it contained fewer individuals. For each anthropometric outcome variable, a test for difference of nine means was performed. Participant characteristics are reported for three broad levels of physical activity: low (
Contents lists available at ScienceDirect
Annals of Epidemiology journal homepage: www.annalsofepidemiology.org
Original article
Physical activity in relation to body size and composition in women in UK Biobank Wenji Guo BS *, Kathryn E. Bradbury PhD, Gillian K. Reeves PhD, Timothy J. Key PhD Cancer Epidemiology Unit, Nuffield Department of Population Health, University of Oxford, Oxford, UK
a r t i c l e i n f o
a b s t r a c t
Article history: Received 8 August 2014 Accepted 25 January 2015 Available online 4 February 2015
Purpose: Physical activity is thought to protect against obesity, but the evidence is limited and few large studies of this topic have direct, objective measures of several different anthropometric variables. We examined the association of self-reported physical activity with measures of total and central adiposity. Methods: Our cross-sectional study included 38,201 premenopausal and 94,592 postmenopausal healthy women aged 40 to 70 years in UK Biobank, recruited from 2006 to 2010. Results: Means for total and vigorous physical activity were 31.3 (SD, 30.8) and 9.7 (SD, 14.8) metabolic equivalent h/wk, respectively, for premenopausal and 34.4 (SD, 33.1) and 8.9 (SD, 15.6) metabolic equivalent h/wk, respectively, for postmenopausal women. Multiple linear regression models showed that in both premenopausal and postmenopausal women, body mass index, body fat mass and percentage, trunk fat mass and percentage, waist and hip circumference, and waist-to-hip ratio were lower in women with higher physical activity (P < .0001). Within each category of total physical activity, a larger proportion of vigorous physical activity was associated with lower adiposity (P < .0001). Conclusions: These findings support the roles of a physically active lifestyle and vigorous exercise in maintaining healthy body size and composition. Higher exercise intensity may be associated with lower adiposity, beyond the influence of exercise frequency and duration. Ó 2015 Elsevier Inc. All rights reserved.
Keywords: Adiposity Body fat percentage Body mass index Cross-sectional studies Intensity Menopause Physical activity
Introduction Obesity is of major, general public health concern because of its association with increased risk of a variety of diseases including diabetes, heart disease, hypertension, stroke, and certain cancers such as breast and endometrial [1]. Although physical activity is widely believed to be an important determinant of body size and composition, the full nature of the relationship is still unclear [2,3]. Although observational studies support an association between exercise and weight-loss maintenance, randomized controlled trials have produced inconsistent results [4]. Questions also remain over the role of vigorous compared with lower intensity physical activity in reducing adiposity and preventing weight gain, and over the relationship between physical activity and different measures of overall versus central adiposity [5,6]. Because risks for some obesity-related diseases such as breast cancer and cardiovascular disease differ by menopausal status, it is of particular interest to examine the associations between physical activity and adiposity
* Corresponding author. Cancer Epidemiology Unit, Nuffield Department of Population Health, University of Oxford, Richard Doll Building, Roosevelt Drive, Oxford OX3 7LF, UK. Tel.: þ44 (0) 1865 289 600; fax: þ44 (0) 1865 289 610. E-mail address: [email protected] (W. Guo). http://dx.doi.org/10.1016/j.annepidem.2015.01.015 1047-2797/Ó 2015 Elsevier Inc. All rights reserved.
separately according to menopausal status in women [7,8]. Some previous large studies have been limited by low numbers of women reporting vigorous physical activity [9]. A number of anthropometric variables have been reported and used in public health recommendations. Because an increase in particular indices of body size may have an effect on specific health outcomes, it is important to assess which indices are likely to be modified by behaviors such as exercise. We report here a crosssectional analysis of associations between reported levels of overall and of vigorous physical activity and several objective measures of body size and composition in more than 132,000 premenopausal and postmenopausal women. In particular, we assess the hypothesis that physical activity is related to body size and composition and that associations may vary by particular measures of adiposity. This research has been conducted using the UK Biobank resource, a nationwide study of approximately 500,000 UK adults. Methods Data source Data were obtained by application to UK Biobank (reference number 3248, approved in August 2013). Details of the rationale,
W. Guo et al. / Annals of Epidemiology 25 (2015) 406e413
design, and survey methods for UK Biobank have been described elsewhere [10], and information on data available and access procedures are given on the study Web site (http://www.ukbiobank.ac. uk/). UK Biobank has approval from the North West Multi-centre Research Ethics Committee, the National Information Governance Board for Health and Social Care in England and Wales, and the Community Health Index Advisory Group in Scotland. All participants provided written informed consent. Study participants The complete UK Biobank data set includes 502, 656 UK adults (229,182 men and 273,474 women) between 40 to 70 years of age at recruitment during 2006 to 2010. Because participation was voluntary and the data collection process rigorous, UK Biobank aimed to enhance generalizability rather than to be representative of the UK population. Participant recruitment was conducted via centrally coordinated identification and invitation from population-based National Health Service patient registers of individuals living within a reasonable distance of an assessment center. Participants completed a touchscreen questionnaire during the baseline assessment center visit that included questions on sociodemographics, lifestyle, health and medical history, and sex-specific factors. Menopausal status provided by UK Biobank was self-reported; for these analyses, women without self-reported menopausal status who were older than 53 years at recruitment and/or had had both ovaries removed were categorized as postmenopausal (n ¼ 29,777), and women younger than 45 years who had not undergone a bilateral oophorectomy were categorized as premenopausal (n ¼ 1053). Women were excluded from the analyses if they reported at recruitment a long-standing illness, disability, infirmity, or had unknown status for this variable (n ¼ 87,989), had unknown menopausal status (n ¼ 15,517), were pregnant (n ¼ 121), or had missing data on any of the physical activity variables used in our analyses (n ¼ 70,343). Participants were also excluded if the sum of all walking, moderate, and vigorous time variables was greater than 6720 min/wk as detailed in the International Physical Activity Questionnaire (IPAQ) scoring guidelines (n ¼ 2184), which can be accessed at https://sites.google.com/site/theipaq/scoring-protocol. Included in the analyses were 38,201 premenopausal and 94,592 postmenopausal women. Physical activity Physical activity questions asked on the baseline questionnaire captured the frequency and duration of three different levels of activity (walking, moderate, and vigorous). Participants were asked how many days per typical week they spent engaged in each category of activity. For each category in which an answer of one or more days was given, the participant was then asked the number of minutes spent on the activity during a typical day. Questions were adapted from the IPAQ short form, a validated survey instrument [11]. Questions are listed in Supplementary Table 1 and are available to view on the UK Biobank Web site (http://biobank.ctsu.ox.ac.uk/ crystal/). We used metabolic equivalents (METs) to quantify physical activity; 1 MET is expended by sitting quietly for 1 hour, and the MET value reflects the ratio of energy expended per kilogram of body weight per hour to that expended when sitting quietly [12]. The number of minutes per day engaged in each level of activity was multiplied by the respective MET score for that level of activity. MET minutes per day were converted to MET hours per week. The total amount of METs was calculated by summing total METs from each activity level. In line with IPAQ guidelines [11], physical activity of less than 10 min/d for walking, moderate, or vigorous activity was recoded to 0.
407
Each category was assigned the following MET hour values: 3.3 for walking, 4.0 for moderate physical activity, and 8.0 for vigorous physical activity [11]. Because individuals are estimated to expend 1 MET/h sitting quietly, we report physical activity as excess METs [13]. Excess METs were calculated by subtracting one from the MET value multiplier for each category, giving values of 2.3 for walking, 3.0 for moderate physical activity, and 7.0 for vigorous physical activity. To assess the importance of vigorous physical activity relative to total physical activity, vigorous physical activity was divided by total physical activity to generate a ratio of vigorous-to-total physical activity. The median ratio of vigorous-to-total physical activity in participants who engaged in any vigorous physical activity was 33%. For analysis, participants were grouped into three categories of vigorous-to-total physical activity: zero percent vigorous physical activity, less than 33% vigorous physical activity, and more than 33% vigorous physical activity. Anthropometry and body composition At the UK Biobank baseline interview, trained staff used standard procedures to measure and record standing height using the Seca 202 device (Seca, Hamburg, Germany). The Wessex non-stretchable sprung tape (Wessex, United Kingdom) measure was used to measure waist and hip circumference. The Tanita BC-418MA body composition analyzer (Tanita, Tokyo, Japan) was used to assess bioimpedance measures including body fat percentage, whole body fat mass, trunk fat percentage, and trunk fat mass. UK Biobank derived body mass index (BMI) by dividing weight (kilogram) by the square of standing height (square meter). We derived waist-to-hip ratio (WHR) by dividing waist circumference by hip circumference. Statistical analyses Multiple linear regression models were used to examine the association between physical activity and the various anthropometric and body composition measures. Amount of physical activity was categorized into nine groups to obtain an approximately even distribution of participants (0,1e4.9, 5e9.9,10e14.9,15e24.9, 25e34.9, 35e49.9, 50e74.9, and 75 excess MET-h/wk) and the figures show the mean within each category. Those who did no physical activity were placed in a separate category even though it contained fewer individuals. For each anthropometric outcome variable, a test for difference of nine means was performed. Participant characteristics are reported for three broad levels of physical activity: low (
