This study examined the joint associations of total time spent in six leisure-time sedentary behaviours, and in leisure-time physical activity, with the odds of being overweight or obese. As expected, those who spent more time in sedentary behaviours and were not sufficiently physically active had an increased likelihood of being overweight or obese: the odds of being overweight or obese were 2.3 times higher and the odds of being obese were 3.7 times higher compared to those with low sedentary behaviour time and sufficient physical activity. The combination of less time in sedentary behaviours and insufficient physical activity and that of more sedentary behaviour time and sufficient physical activity were similarly associated with the risk of being overweight or obese. In the analysis conducted on the whole sample (men and women combined), these two groups had more than 50% higher odds of overweight or obesity and almost twice the odds of obesity, compared to those who had less sedentary behaviour time and were sufficiently physically active. It can be argued that reduced energy expenditure from lack of light-, moderate- or vigorous-intensity physical activity or increased energy intake which could occur while being engaged in sedentary behaviours (or both) may be responsible for the increased likelihood of overweight and obesity observed in this study.
These findings suggest that high levels of overall sedentary behaviour time may contribute to obesity potentially as much as does lack of moderate to vigorous physical activity. They also suggest that even if adults meet the public health guideline for leisure-time physical activity [20
], they may have a high risk of being overweight or obese if they spend a large amount of time in sedentary behaviours during leisure. Our findings are consistent with past studies that showed the associations of a particular sedentary behaviour (TV viewing) with weight status independent of physical activity levels [7
]. A weak relationship between sedentary behaviours and moderate to vigorous physical activity, which has been reported in previous studies [7
], was also confirmed in this study.
It was found that participants on average reported about 4 hours on LTSB per day. This is comparable with findings obtained from Dutch workers (4.7 hours/day) [26
], and from middle-aged French adults (3.4 hours/day, which included only TV watching, computer use and reading) [27
]. TV viewing was the largest component, occupying 45% of the total LTSB that was assessed. Among those who were categorised as having a high volume of LTSB, TV viewing time occupied an even larger proportion, which suggests that prolonged TV viewing time may contribute to a higher volume of total sedentary behaviour time.
Men and women differed in the proportions of those who were overweight or obese, and in the proportions of membership to the combined LTSB/LTPA categories: more men belonged to the overweight or obese category, and to the category of high LTSB and sufficient LTPA. Despite these differences, regression analyses found a similar pattern of associations between the combined categories and being overweight or obese in men and women, although the odds for the combination of low LTSB and insufficient LTPA and that of high LTSB and sufficient LTPA were not significant in men, potentially due to a smaller sample size. Thus, both in men and in women, the findings suggest that the risk of overweight or obesity associated with more sedentary leisure time is as high as not being sufficiently physically active during leisure time. However, past studies have shown stronger associations of sedentary behaviour with metabolic health risks in women [7
]. Given the gender imbalance in our study sample, we are reluctant to place an emphasis on any apparent gender differences in the findings. Further research should investigate whether and to what extent gender may moderate the relationship between sedentary behaviours and health indictors, and the potential mechanisms (behavioural or biological) that may underlie the differences between men and women.
We found that socio-economic (education and income) and work status were related to sedentary behaviour and physical activity. High levels of LTSB appeared to be more common among those in lower socio-economic groups and in those without work (who may have more discretionary time available to them). A study in The Netherlands found an association between physical inactivity and neighbourhood social and environmental inequalities [29
]. Although physical activity and sedentary behaviour are not closely correlated, it may be hypothesised that less opportunities for social and recreational activity in neighbourhoods may have a bearing on the time spent being sedentary. Indeed, a recent study has shown that women living in "walkable" neighbourhoods tend to spend less time in TV viewing, compared to those living in less-walkable areas [30
]. Further research is needed to examine how social and environmental factors may be related to prolonged sedentary behaviour time.
Methodological limitations include the cross-sectional nature of the study, which precludes causal inferences, and self-report measures of weight, height, sedentary behaviours and physical activity. Longitudinal studies comparing the effects of reducing sedentary behaviours and increasing physical activity are needed to examine the possible causal nature of the relationships that we have identified. Also as stated before, the low proportion of men in our sample limits our ability to examine the gender differences that have emerged in previous studies.
This study adds to a growing body of evidence supporting the potential health benefits of reducing sedentary behaviour time. Sedentary behaviours should not be considered as simply being the bottom end of the physical activity continuum, and should be addressed specifically and explicitly, with attention to their distinct health impacts and determinants [23
]. Our findings suggest the need for a stronger focus on reducing time spent in leisure-time sedentary behaviours to decrease the risk of obesity and associated chronic diseases.