As regular readers of Obesity Panacea will know, my current research focuses on the health impact of sedentary behaviour (e.g. sitting). In the past 5-10 years there has been a growing body of evidence that suggests that the more you sit, the greater your risk of developing a chronic disease like diabetes or heart disease, and of dying prematurely (you can find a brief review of the research here).
One factor that may link sedentary behaviour with increased morbidity and mortality is the accumulation of visceral fat (see figure below), which has been linked with various chronic diseases and even death. For example, see this study by our former labmate Jen Kuk, which found that visceral fat was an independent predictor of premature death in men. While other types of body fat (e.g. butt fat) don’t tend to have a huge health impact, excess visceral fat is definitely a bad thing (more details on how body fat distribution influences health here).
Previous research has linked sedentary behaviour with increased waist circumference (which includes both visceral and subcutaneous fat), but no one has looked directly at whether sitting is associated with increased accumulation of visceral fat. Thus, in a study published earlier this month in PLOS ONE, my colleagues and I examined the relationship between sedentary behaviour and metabolic risk factors over a 6-year period in participants of the Quebec Family Study.
What did we do?
The Quebec Family Study is a longitudinal study which was originally designed to examine the role of genetics in the development of obesity and related risk factors. The study included a wide variety of tests, including the measurement of visceral and subcutaneous abdominal fat using computed tomography (similar to the technology used to create the above image), as well as measurement of important metabolic risk factors like glucose, insulin, and blood lipids. Physical activity and sedentary behaviour were recorded using a self-report questionnaire. For the present analysis we looked at 147 men and 169 women who had data for all variables at both baseline and the 6-year follow-up.
What did we find?
To be honest, not that much (at least statistically speaking). After adjusting for confounding variables like physical activity and food intake, sedentary behaviour at baseline was not associated with changes in visceral adiposity or any other marker of cardiometabolic risk. There was a relationship between changes in sedentary behaviour and increased waist circumference – every 15-minute increase in sedentary behaviour from baseline to follow-up was associated with a 0.13 cm increase in waist circumference (95% CI = 0.02, 0.25). But it’s important to point out that there was no association between changes in sedentary behaviour and changes in visceral adiposity or other markers of cardiometabolic risk.
The above figure nicely illustrates the lack of relationship between sedentary time and the accumulation of visceral fat in our study. In the top panel, participants are broken into 3 groups based on their level of sedentary behaviour at baseline (low, medium and high). In the bottom panel, they are broken into groups based on whether their level of sedentary behaviour increased, decreased or remained constant over the 6-year study. In both cases, you can see there there is absolutely no clear difference across the three groups. In other words, no matter what the sedentary behaviour level at baseline, and no matter whether sedentary behaviour increased or decreased over the course of the study, it had no influence on the accumulation of visceral fat.
What is the take-home message?
At least in this dataset, sedentary behaviour doesn’t seem to be associated with the accumulation of visceral fat or development of metabolic risk. It was associated with increased waist circumference, but not with increased visceral fat – and the main reason we measure waist circumference is because it’s a proxy measure for visceral fat. So it’s difficult to interpret that increase in waist circumference as being clinically meaningful in this situation.
How is it possible that sedentary behaviour can be associated with increased risk of cardiovascular disease in other studies, when we didn’t see any sort of relationship between sedentary behaviour and risk factors for cardiovascular disease? Our study was relatively small, and our measure of sedentary behaviour was self-reported, both of which could have influenced our findings. It may also be that some sedentary behaviours (e.g. TV viewing) are more closely associated with health risk than others, but our questionnaire didn’t allow us to break sedentary behaviour into different categories.
On the other hand, we were able to directly measure changes in visceral fat and other markers of metabolic risk in these individuals, which is extremely high quality data. So obviously this study raises more questions than it answers, and is a reminder of why you can never interpret any individual study as if it existed in a vacuum, no matter how awesome the study may be. And I should point out that just because these are null findings, doesn’t necessarily make them any less exciting or important. If you have any thoughts on how to square these findings with previous studies like this one by Katrien Wijndaele, I would love to hear them in the comments.
On a strictly personal note this study was exciting for me for a few reasons – I got to work with some of the biggest names in obesity research including Claude Bouchard (editor of The Handbook of Obesity), Angelo Tremblay, Jean-Pierre Després, Mark Tremblay and Jean-Philippe Chaput. A Pubmed Search for Claude Bouchard brings up more than one thousand papers – yikes. So that was fun. This paper was also my first paper as first author in PLOS ONE, and my first original research paper from my current lab in Ottawa. With any luck there will be several more coming down the pipeline as I finish up the rest of my PhD thesis.
Since this paper was published in PLOS it is available online for free. The paper has a lot of tables with info that I just skimmed over in this post, and you can find all of that here in various formats, including powerpoint slides.
Saunders, T., Tremblay, M., Després, J., Bouchard, C., Tremblay, A., & Chaput, J. (2013). Sedentary Behaviour, Visceral Fat Accumulation and Cardiometabolic Risk in Adults: A 6-Year Longitudinal Study from the Quebec Family Study PLoS ONE, 8 (1) DOI: 10.1371/journal.pone.0054225