TAKING SHORT WALKING BREAKS FOUND TO REVERSE NEGATIVE EFFECTS OF PROLONGED SITTING

An  Indiana University study has found that three easy -- one could even say slow -- 5-minute walks can reverse harm caused to leg arteries during three hours of prolonged sitting.

Sitting for long periods of time, like many people do daily at their jobs, is associated with risk factors such as higher cholesterol levels and greater waist circumference that can lead to cardiovascular and metabolic disease. When people sit, slack muscles do not contract to effectively pump blood to the heart. Blood can pool in the legs and affect the endothelial function of arteries, or the ability of blood vessels to expand from increased blood flow.

This study is the first experimental evidence of these effects, said Saurabh Thosar, a postdoctoral researcher at Oregon Health & Science University, who led the study as a doctoral candidate at IU's School of Public Health-Bloomington.

"There is plenty of epidemiological evidence linking sitting time to various chronic diseases and linking breaking sitting time to beneficial cardiovascular effects, but there is very little experimental evidence," Thosar said. "We have shown that prolonged sitting impairs endothelial function, which is an early marker of cardiovascular disease, and that breaking sitting time prevents the decline in that function."

The researchers were able to demonstrate that during a three-hour period, the flow-mediated dilation, or the expansion of the arteries as a result of increased blood flow, of the main artery in the legs was impaired by as much as 50 percent after just one hour. The study participants who walked for 5 minutes each hour of sitting saw their arterial function stay the same -- it did not drop throughout the three-hour period. Thosar says it is likely that the increase in muscle activity and blood flow accounts for this.

"American adults sit for approximately eight hours a day," he said. "The impairment in endothelial function is significant after just one hour of sitting. It is interesting to see that light physical activity can help in preventing this impairment."

The study involved 11 non-obese, healthy men between the ages of 20-35 who participated in two randomized trials. In one trial they sat for three hours without moving their legs. Researchers used a blood pressure cuff and ultrasound technology to measure the functionality of the femoral artery at baseline and again at the one-, two- and three-hour mark.

In the second trial, the men sat during a three-hour period but also walked on a treadmill for 5 minutes at a speed of 2 mph at the 30-minute mark, 1.5-hour mark and 2.5-hour mark. Researchers measured the functionality of the femoral artery at the same intervals as in the other trial.

CURB SITTING TIME TO POSSIBLY EXTEND LIFESPAN

Reducing sedentary activity appears to lengthen telomeres, which sit on the end of chromosomes, the DNA storage units in each cell, the findings show

Telomeres are important because they stop chromosomes from 'fraying' or clumping together and 'scrambling' the genetic codes they contain, performing a role similar to the plastic tips on the end of shoelaces, to which they have been likened.

Longevity and a healthy lifestyle have been linked to telomere length, but whether physical activity can make any difference, is not clear.

The researchers therefore analysed the length of chromosomal telomeres in the blood cells of 49 predominantly sedentary and overweight people in their late 60s, on two separate occasions, six months apart.

All 49 participants had been part of a previously reported clinical trial in which half of them had been randomly assigned to a tailored exercise program over a period of six months, and half had been left to their own devices.

Levels of physical activity were assessed using a seven day diary and a pedometer to measure the number of footsteps taken every day, while the amount of time spent sitting down each day was gleaned through a validated questionnaire.

The time spent exercising as well as the number of steps taken daily increased significantly in the group following the exercise program, while the amount of time spent seated fell in both groups.

Various risk factors for heart disease and stroke also improved in both groups, particularly those on the exercise program, who also lost a great deal more weight than their counterparts left to their own devices.

But increases in physical activity seemed to have less of an impact than reductions in sitting time, the findings showed.

The number of daily steps taken was not associated with changes in telomere length, while an increase in moderate intensity physical activity was linked to a shortening in telomere length, although this was not significant.

But a reduction in the amount of time spent sitting down in the group on the exercise program was significantly associated with telomere lengthening in blood cells.

"In many countries formal exercise may be increasing, but at the same time people spend more time sitting," write the researchers. "There is growing concern that not only low physical activity...but probably also sitting and sedentary behaviour is an important and new health hazard of our time."

They admit that their study is small, and caution that it needs to be repeated in other larger groups, and in other tissues, such as skeletal muscle and fat cells.

But they say that their findings corroborate other research on the impact of time spent sitting down, and conclude: "We hypothesise that a reduction in sitting hours is of greater importance than an increase in exercise time for elderly risk individuals."