Journal of Physical Activity and Health, 2015, 12, 1589  -1600 http://dx.doi.org/10.1123/jpah.2014-0370 © 2015 Human Kinetics, Inc.

ORIGINAL RESEARCH

Leisure-Time Physical Activity Does not Attenuate the Association Between Occupational Sedentary Behavior and Obesity: Results From Alberta’s Tomorrow Project Joshua A. Nicholas, Geraldine Lo Siou, Brigid M. Lynch, Paula J. Robson, Christine M. Friedenreich, and Ilona Csizmadi Background: Sedentary behavior has been proposed as a risk factor for obesity that is distinct from physical inactivity. This study aimed to examine the association between occupational sedentary behavior and obesity, and to determine if this association is independent of leisure-time physical activity (LTPA). Methods: Fully employed participants enrolled between 2001 and 2008 to Alberta’s Tomorrow Project, a prospective cohort study in Alberta, Canada, were studied (n = 12,409). Associations between occupational sedentary behavior and waist circumference (WC), waist-to-hip ratio (WHR), and body mass index (BMI) were examined using multiple binary and multinomial logistic regressions. Results: In men, a positive association was observed between daily occupational sedentary hours and WC, WHR, BMI, and with high risk profiles that incorporated both BMI and WC (P < .01). Controlling for vigorous-intensity LTPA in all models strengthened associations between sedentary behavior and measures of obesity. In contrast, inverse associations were observed for occupational sedentary hours and WHR for women (P < .05). Conclusions: In fully employed men, occupational sedentary behavior was positively associated with obesity risk that was not attenuated by physical activity. In women, an increase in obesity risk was not observed with sedentary behavior. Gender differences in the health effects of sedentary behavior require further study. Keywords: sedentary behavior, occupational sitting

Obesity is a risk factor for diabetes, some cancers, coronary heart disease and overall mortality.1–3 Based on data extracted from the National Health Expenditure Database forecast for 2006, the direct cost of overweight and obesity in Canada, without the inclusion of comorbidities, was estimated to be $6 billion.4 Population health interventions directed at obesity prevention and reduction are critical for a sustainable healthcare system.5 An aspect of lifestyle that warrants investigation is sedentary behavior, as it may have metabolic consequences distinct from those observed with not engaging in moderate-to-vigorous intensity physical activity (MVPA). Indeed, there is increasing evidence that sedentary behavior is a contributing factor to obesity, and obesityrelated disorders such as diabetes, high blood pressure and certain cancers.6–10 Hence, the phenomenon of the ‘active couch potato’ which refers to individuals who perform physical activity at levels that meet or exceed current guidelines, but who are sedentary for the majority of the day.11 Describing the health effects of sedentary behavior is therefore of public health importance. Previous studies of sedentary behavior have mainly addressed activities performed during leisure time, such as watching

Nicholas ([email protected]) is with the University of Calgary Cumming School of Medicine, Calgary, Alberta, Canada. Lo Siou is with the Dept of Cancer Measurement, Outcomes, Research, and Evaluation (C-MORE), CancerControl Alberta, Alberta Health Services, Calgary, Alberta, Canada. Lynch is with The Cancer Epidemiology Center, Cancer Council Victoria, Melbourne Australia. Robson is with the Dept of Cancer Measurement, Outcomes, Research, and Evaluation (C-MORE), CancerControl Alberta, Alberta Health Services, Edmonton, Alberta, Canada. Friedenreich and Csizmadi are with the Dept of Cancer Epidemiology and Prevention Research, CancerControl Alberta, Alberta Health Services, Calgary, Alberta, Canada.

television.12,13 However, occupational sedentary behavior is a particularly important exposure, since, evidence suggests that fully employed adults in North America spend the greatest proportion of each work day at work.14 Objective measures of sedentary behavior reveal that 66% or more of the workday among office workers is spent sitting.15,16 There is some evidence that workers who engage in high volumes of sitting have a significantly higher risk of being overweight or obese than active workers, despite a greater likelihood of engaging in LTPA.17,18 However, in a systematic review of the health risks associated with occupational sitting, a clear association with obesity was not found.19 Without convincing evidence for the potentially deleterious health impacts of occupational sedentary behavior, many workplace interventions may encourage increasing structured physical activity but may overlook opportunities to reduce occupational sedentary time.20,21 There is an urgent need for a better understanding of the association between occupational sedentary behavior and obesity. Such research is essential to inform workplace interventions that aim to improve the health and wellbeing of employees. The objective of this study was to examine the association between occupational sedentary behavior and obesity and to determine whether this association is attenuated by leisure-time physical activity.

Methods Study Design and Subjects This study is a cross-sectional design with an analysis of data from Alberta’s Tomorrow Project, a longitudinal cohort study based in Alberta, Canada. Details of the recruitment methods for Alberta’s Tomorrow Project have been described elsewhere.22 In brief, participants aged 35 to 69 years, living in Alberta, Canada, with no previous history of cancer other than nonmelanoma skin 1589

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cancer, were recruited by telephone using random digit dialing. Baseline data for Alberta’s Tomorrow Project were collected by questionnaire. The Health and Lifestyle Questionnaire (HLQ) ascertained information on employment status (full-time, parttime, not employed/homemaker/student/other, or retired), education, marital status, ethnicity and smoking status. The National Cancer Institute’s (NCI) Diet History Questionnaire I, a food frequency questionnaire modified for use in Canada (C-DHQ I) was completed by participants to provide information pertaining to past-year dietary intake.23 The Past-Year Total Physical Activity Questionnaire (PYTPAQ), described in a subsequent section, was used to assess physical activity and occupational sedentary behavior.24 Participants enrolled between 2001 and 2008 who had reported working full-time (defined as reporting full-time employment on the HLQ and at least 30 hours of occupational time per week on the PYTPAQ) and had completed the C-DHQ I, PYTPAQ and HLQ questionnaires were eligible for this analysis (n = 13,023). The PYTPAQ was designed to assess occupational sedentary behavior but not all domains of sedentary behavior. Because part-time workers may have had more opportunity for leisure-time sedentary behavior, which we could not control for a priori, we judged that it would be most valid to examine only those subjects who were employed full-time. Participants were excluded if they had a history of cancer other than nonmelanoma skin cancer before enrolment, reported being pregnant, were recruited as “second in household” in the first wave of recruitment, reported a body mass index (BMI) that was below the healthy range (< 18.5 kg/m2) or reported indeterminate sex (n = 344). Ethics approval for baseline data collection in Alberta’s Tomorrow Project was obtained from the Research Ethics Committees of the Alberta Cancer Board (subsequently the Alberta Cancer Research Ethics Committee at Alberta Health Services) and the University of Calgary, Alberta, Canada.

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Leisure-Time Physical Activity Does not Attenuate the Association Between Occupational Sedentary Behavior and Obesity: Results From Alberta's Tomorrow Project.

Sedentary behavior has been proposed as a risk factor for obesity that is distinct from physical inactivity. This study aimed to examine the associati...
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