As someone who regularly works at a computer both at work and at home, sedentary activity is a part of my daily life. Unfortunately, my desk is the standard kind that requires me to sit on a chair; I can only dream of the kind that has a treadmill to encourage movement as I work. The health consequences of sitting for long periods of time have been covered in research papers and other blogs, but a recent paper highlighted how it is not only how long we are sedentary but how often we step away from our desks and sofas that affects our health.
Previous research has shown negative effects on health if people are too sedentary, but these studies were limited both in number and diversity of people studied. Healy et al. set out to examine a large, ethnically diverse group of adults (4,757) and determine how active or inactive they were while measuring various cardiometabolic markers including waist circumference, HDL cholesterol, C-reactive protein and insulin sensitivity. Age, behavior (smoking, food consumption, alcohol) and sociodemographic information was obtained. Physical activity was assessed using an accelerometer worn for seven days for at least ten hours and broken down into sedentary (<100cpm), light-intensity activity (100–1,951cpm) or moderate–vigorous intensity physical (exercise) activity (≥1,952cpm). Activity counts had date and time stamps to derive the length and intensity of movement.
The participants were part of the US National Health and Nutrition Examination Survey (NHANES) and from an initial sample size of over 20,000, 4,757 people were in the final analyzed sample. The association between total sedentary time (and breaks from sedentary periods) with the cardiovascular and metabolic markers were assessed using linear regression, plotting a straight line for a cluster of data.
The population studied was 50% female with an average age of 46.5 years. Each participant’s time was spent an average nearly 8.5 hours (of average accelerometer data) per day being sedentary and approximately 15 minutes per day classified as exercising. The breaks in sedentary time occurred an average of 92.5 times per day with a mean duration of movement just over four minutes.
Measures of cardiovascular and metabolic health (especially waist circumference) and total sedentary time had a negative correlation, consistent with other studies. Overall, women were more sedentary compared to men, but took more breaks and had better numbers for the measures assessed (e.g., HDL-cholesterol and C-reactive protein). Waist circumference and C-reactive protein, a measure of inflammation and associated with increased risk of cardiovascular disease, also correlated to the number of interruptions in sedentary time; that is, the more breaks there were, the lower the values measured.
Most correlations between the sexes were identical except for an associated between sedentary time and HDL-cholesterol (total sedentary time = higher cholesterol numbers in men; greater number of breaks = lower numbers in women). Waist circumference showed the greatest differences among reported ethnicity. Non-Hispanic whites had a negative correlation to waist circumference and sedentary activity; there was no association for Mexican Americans and a beneficial association for non-Hispanic blacks. Also the number of interruptions in sedentary time had a positive correlation only for non-Hispanic whites; the other groups had no association.
The gist of this study is time spent being sedentary puts people at greater risk for cardiovascular disease and diabetes, not a new message. Not only was being sedentary bad, but the negative consequences on health are independent of time spent exercising. Furthermore, interruptions of sedentary time were beneficial to the waistline and C-reactive protein, both of which are risk factors for heart disease. This study has implications for all of us who spend hours behind a desk for our work. As much as I enjoy my time spent on the computer or watching television, I realize I need to take more breaks from my desk or sofa even if they do interrupt the flow of my writing or focus on a task. So, if you have reached the end of my post, please take a break and walk a lap around your building. Your waistline and heart will thank you!
1. Healy, G.N., Matthews, C.E., Dunstan, D.W., Winkler, E.A. and Owen, N. (2011). Sedentary time and cardio-metabolic biomarkers in US adults: NHANES 2003-06. European Heart Journal PMID: 21224291
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