Elizabeth Pope

Too much sedentary time is dangerous for active exercisers as well as couch potatoes.
AARP Bulletin March 11, 2011

"Sitting is the new smoking," says Marc T. Hamilton, a physiologist at Pennington Biomedical Research Center in Baton Rouge, La. "These days we sit more than we sleep — an average of 10 hours a day — and it's a serious health hazard."

A growing body of research shows that "heavy sitters" have higher risks of heart disease, diabetes, weight gain and early death. A recent British study found that more than four hours of leisure time spent in front of a TV or computer doubled the risk of heart disease in middle-age adults. The really bad news? Other new studies indicate even "active couch potatoes" who exercise regularly but sit the rest of the day may be at risk of life-threatening disease.

Age 50-plus adults remember walking to school, washing dishes, hanging laundry, raking leaves and shoveling snow. Much of that activity has disappeared, and since the advent of the personal computer and cable TV in the 1980s, Americans, young and old, barely get out of a chair. "Technology has engineered physical activity out of our day," Hamilton says. Men and women over age 65 are among the most sedentary groups in the United States, with more than four in 10 getting no leisure-time physical activity at all.

Some researchers now think too much sitting harms the body in a different way from too little exercise. In an early 1950s study of British workers, bus drivers had twice the number of fatal heart attacks as conductors who were on their feet all day. Standing or walking causes tiny muscle contractions that begin a cascade of important metabolic and genetic processes breaking down fats and sugars in the blood. Sitting or lolling about on the couch appears to shut off an important enzyme (lipoprotein lipase, or LPL) that "acts like a vacuum cleaner for fat in the blood," Hamilton says. In Hamilton's animal studies, mice and rats developed higher blood fats and lower good cholesterol levels within hours of being immobilized.

New research into "inactivity physiology" indicates that even formal exercisers — the lunchtime gym rats and early morning brisk walkers — nullify benefits of a healthy workout if they sit in a car, at a desk or on a couch the rest of the day. In a study of 11,000 Australian adults, physically active women who watched lots of television had larger waist circumferences and were more likely to develop metabolic syndrome, a precursor to diabetes. A University of South Carolina study of middle-age men found that those who sat more than 23 hours a week (watching TV or sitting in a car) had a far greater risk of cardiovascular disease than those who sat less than 11 hours.

Sedentary behavior is a real threat to older adults, says Toni Yancey, M.D., author of Instant Recess and an advocate of 10-minute exercise breaks. "There's a spike in physical activity around age 64 when people first retire, but after that activity levels tend to plummet," she says. " And physical activity in older adults is crucial so they don't lose muscle mass." There is no consensus yet about how much sitting is safe, but researchers expect to have recommendations in the near future. Until then, they advise reducing overall sedentary time or interrupting prolonged bouts of sitting. Even a one-minute break to stand up and walk around is good for the waistline and the heart, according to a recent Australian study.

Hamilton predicts reduced sedentary time will soon be accepted as the third pillar of disease prevention, included in public health guidelines: "The message will be that good health isn't just about eating well and getting enough exercise. You need to stand up and walk around, too."