Australasian Science: Australia's authority on science since 1938

Take a Break from Sitting

By Stephen Luntz

Overweight workers in sedentary jobs should take frequent short activity breaks to reduce the negative impacts of sitting for too long, a paper in Diabetes Care suggests.

Considerable recent evidence has emerged to indicate that long periods of sitting pose dangers beyond lack of exercise alone (AS, July/Aug 2011, p.11). Researchers have speculated that getting up frequently, even if only for short walks to the printer, may ameliorate the damage, but until now this has been unproven.

A/Prof David Dunstan of the Baker IDI Heart and Diabetes Institute has provided support for this idea by monitoring study participants’ glucose levels after high calorie meals. He found that 2-minute breaks for either light or moderate intensity activity helped the body control its blood sugar levels.

“When we eat, we get rises in blood glucose. With larger and more frequent rises in blood glucose, we gradually accumulate damage to the walls of our veins and arteries. This increases our susceptibility to heart disease,” Dunston says. “So, we want to minimise these rises in order to improve our health outcomes.

“In a controlled laboratory environment that mimicked the typical patterns of desk-bound office workers, participants who interrupted their sitting time with regular activity breaks showed up to 30% improvement in the body’s response to a meal containing glucose.”

Dunstan says he has “no definitive mechanism” as to why light exercise proved as effective as more energetic activity. “You have to look at what it is compared to,” he speculates. “When sitting, there is a loss of blood flow and an absence of muscular contraction. We know this contraction is essential, and it seems likely counteracting the muscle disuse is what leads to benefits.”

Although the study examined overweight participants, Dunstan is confident that similar benefits would apply generally.

Good glucose control is associated with lower rates of cardiovascular disease, although Dunstan says it would be difficult to estimate how large a benefit could be expected from the observed 30% reduction in glucose spikes.

Dunstan had his subjects engage in 2 minutes of exercise every 20 minutes. He says these figures were chosen because an epidemiological study had found that people who broke up their sitting three or four times per hour had “a better health profile”.

Dunstan also wanted the total exercise time to roughly match the 30 minutes/day considered a minimum for good health, even though this is usually recommended to take place in bursts of at least 10 minutes.

The value of the results was emphasised when an epidemiological study by Dr Hidde van der Ploeg of the University of Sydney, published in Archives of Internal Medicine, found that people over the age of 45 who sit for more than 11 hours/day have a 40% increased risk of dying within a 3-year period compared with those who sit for fewer than 4 hours/day.