Sitting time and work patterns as indicators of overweight and obesity in Australian adults.
BACKGROUND
Increasing levels of physical inactivity and sedentariness are contributing to the current overweight and obesity epidemic. In this paper, the findings of two recent studies are used to explore the relationships between sitting time (in transport, work and leisure), physical activity and body mass index (BMI) in two contrasting samples of adult Australians.


METHODS
Data on sitting time, physical activity, BMI and a number of demographic characteristics were compared for participants in two studies-529 women who were participants in a preschool health promotion project ('mothers'), and 185 men and women who were involved in a workplace pedometer study ('workers'). Relationships between age, number of children, physical activity, sitting time, BMI, gender and work patterns were explored. Logistic regression was used to predict the likelihood of being overweight or obese, among participants with different physical activity, sitting time and work patterns.


RESULTS
The total reported time spent sitting per day (across all domains) was almost 6 h less among the mothers than the workers (P<0.001), and compared with the mothers, a significantly greater proportion of the workers was classified as overweight or obese (BMI > or =25 kg/m(2)). Univariate analysis found that, compared with men in full-time work, women who worked full-time (OR=0.42, CI: 0.24-0.74), part-time (OR=0.35, CI: 0.20-0.59) or in full-time home duties (OR=0.51, CI: 0.29-0.88) were about half as likely to be overweight or obese. Participants who reported high daily levels of sitting (> or =7.4 h) were also significantly more likely than those who reported 'low' levels (<4.7 h/day) to be overweight or obese (OR=1.68, CI: 1.16-2.42). Multivariate analysis (including physical activity, work patterns and sitting time) confirmed that full-time and part-time working women (but not 'home duties' women) were less likely to report BMI > or =25 kg/m(2) than full-time working men (full-time: OR=0.44, CI: 0.25-0.78; part-time: OR=0.45, CI: 0.24-0.86), but the OR for BMI > or =25 among those in the high sitting category was attenuated (OR=1.61, CI 0.96-2.71).


CONCLUSIONS
The findings suggest a need for inclusion of measures of both activity and inactivity in future studies, so that the complex relationships between these behavioural determinants of BMI can be clarified.
School of Human Movement Studies, University of Queensland, Australia. wbrown@hms.uq.edu.au
W J
WJ
Brown
Y D
YD
Miller
R
R
Miller
D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D015992:Body Mass Index; D005260:Female; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D009035:Mothers; D015999:Multivariate Analysis; D009765:Obesity / Q000209:etiology*; D016272:Occupational Health; D005082:Physical Exertion; D011187:Posture; D012307:Risk Factors; D012737:Sex Factors