Blog | Wednesday, March 28, 2012

QD: News Every Day--People who exercise a little but sit a lot still have higher mortality risk

Office workers face a 15% higher mortality risk from all that sitting, but the truly sedentary, those who go home and sit for three more hours, face a 40% higher risk.

Prolonged sitting is a risk factor for all-cause mortality, independent of physical activity. Researchers wanted to put some numbers to this, so they linked survey data from nearly 222,500 individuals 45 years or older from the Medicare registry of New South Wales, Australia, from February 2006 through December 2010.

Results appeared in the March 26 issue of Archives of Internal Medicine.

During nearly 621,700 person-years of follow-up, more than 5,400 deaths occurred. Compared with less than 4 hours per day sitting, adjusting for physical activity and other confounders, all-cause mortality hazard ratios were:
--4 to less than 8 hours sitting, 1.02 (95% CI, 0.95 to 1.09),
--8 to less than 11 hours sitting, 1.15 (95% CI, 1.06 to 1.25), and
--11 or more hours sitting, 1.40 (95% CI, 1.27 to 1.55).

The association was consistent after accounting sex, age, body-mass index (BMI) and physical activity, as well as between healthy participants and those with cardiovascular disease or diabetes. There was a clear dose-response relationship for sitting time and physical activity that persisted even among those with relatively high levels of physical activity.

Researchers pointed to prolonged sitting's effect on metabolism, including increased plasma triglycerides, decreased high-density lipoproteins and decreased insulin sensitivity, as well as changes to carbohydrate metabolism.

"Our findings suggested not only an association between sitting and all-cause mortality that was independent of physical activity but, because the findings persisted after adjustment and stratification for BMI, one that also appears to be independent of BMI," the researchers wrote.

An editorialst wrote that even people who exercise a half hour a day can be sedentary for the other 15.5 waking hours. "To put this in perspective, 30 minutes of physical activity is as protective an exposure as 10 hours of sitting is a harmful one."