Are we just sitting ducks? (On How Sinnting affects your Health)

Are we just sitting ducks? (On How Sinnting affects your Health)

The Straits Times dated 18th April 2011, Monday

Diet and exercise won't offset sedentary time, which can kill: Study

NEW YORK: A growing body of evidence suggests that sitting around too much has consequences far worse than a sore back or a spare tyre: It can prove lethal.

Worse, even a balanced diet and regular aerobic exercise are not enough to offset sedentary time, a report in the New York Times said, quoting researchers in the emerging field of inactivity studies, which is challenging long-held beliefs about human health and obesity.

Dr James Levine, a researcher at the Mayo Clinic in Rochester, Minnesota, stumbled on some surprising facts when he began conducting a series of studies in 2005 to find out why some people gained more weight than others even if they had consumed the same amount of food.

The participants in his study ate in the laboratory for two months and were told not to exercise. In addition, they wore special motion-tracking underwear. Twice a second, 24 hours a day, sensors on the underwear assessed every movement a subject made, whether lying down, walking, standing or sitting.

After assessing how much food each subject needed to maintain his current weight, Dr Levine made them consume an extra 1,000 calories per day. The result: Some of his subjects gained a lot of weight while the others put on little to none. He was stumped as to why this was the case.

'We measured everything, thinking we were going to find some magic metabolic factor that would explain why some people didn't gain weight,' said DrMichael Jensen, a Mayo Clinic researcher who collaborated with Dr Levine on the studies.

But the researchers were stuck for an explanation until they examined the movements of the subjects.

'The people who didn't gain weight were unconsciously moving around more,' Dr Jensen said.

Exercise was forbidden but those who did not pile on the kilos had responded naturally by making more little movements than they had before the overfeeding began, such as taking the stairs, trotting down the hall to the office water cooler or simply fidgeting.

On average, the subjects who gained weight sat two hours more per day than those who did not.

In itself, sitting is no worse than any other daytime physical inactivity but it is what people mostly do when awake.

When one sits, electrical activity in the muscles drops, triggering a number of changes in the body, said Mr Marc Hamilton, another inactivity researcher at Pennington Biomedical Research Centre.

'The muscles go as silent as those of a dead horse,' he told the New York Times, describing the cascade of harmful metabolic effects that follow.

The calorie-burning rate immediately plunges to about one a minute, a third of what it is when walking. Insulin effectiveness, the ability to control blood sugar levels, drops within a day, and the risk of developing Type 2 diabetes rises.

So does the risk of obesity. The enzymes responsible for breaking down fats plunge, causing the levels of good (HDL) cholesterol to fall.

To show that the ill effects of sitting can have a rapid onset, Mr Hamilton recruited 14 young, fit and slender volunteers and recorded a 40 per cent reduction in insulin's ability to take glucose from the blood in the subjects - after just 24 hours of being sedentary.

The unhealthy effects of sitting add up over time, found Ms Alpa Patel, an epidemiologist at the American Cancer Society who tracked the health of 123,000 Americans between 1992 and 2006.

The men in her study who had spent six hours or more a day of their leisure time sitting had an overall death rate that was about 20 per cent higher than the men who sat for three hours or less. The death rate among women who sat for more than six hours a day was about 40 per cent higher.

Another study, published last year in the journal Circulation, looked at nearly 9,000 Australians and found that for each additional hour of television an individual sat and watched each day, the risk of death rose by 11 per cent.

Its author David Dunstan wanted to analyse whether the people who sat watching TV had other unhealthy habits that caused them to die sooner. But he reported that age, sex, education, smoking, hypertension, waist circumference, body-mass index, glucose tolerance status and leisure-time exercise did not significantly modify the associations.

Being sedentary for nine hours a day at the office, it would seem, is bad for health whether you go home and watch TV or do weights.

'Excessive sitting,' Dr Levine said, 'is a lethal activity.'