What do we learn from the study of the 4,512 Scottish men（）

A. Those who watched more TV were sure to suffer heart disease.
B. People sitting more have higher risk of heart disease.
C. People are more likely to die if they don’t exercise.
D. Scottish men were physically active for several hours a week.

Many of us sit in front of a computer for eight hours a day,and then go home and head for the couch to surf the Web or watch television,exchanging one seat and screen for another. Even if we try to squeeze in an hour at the gym, is it enough to counteract all that motionless sitting

A mounting body of evidence suggests not. The latest findings, published this week indicate that the amount of leisure time spent sitting in front of a screen can have such an overwhelming, seemingly irreparable impact on one’s health that physical activity doesn’t produce much benefit.

The study followed 4,512 middle-aged Scottish men for a little more than four years on average. It found that those who said they spent two or more leisure hours a day sitting in front of a screen were at double the risk of a heart attack or other cardiac compared with those who watched less. Those who spent four or more hours of recreational time in front of a screen were 50 percent more likely to die of any cause. It didn’t matter whether the men were physically active for several hours a week--exercise didn’t lessen the risk associated with the high amount of sedentary screen time. A study last year found that men who spent more than 23 hours a week watching TV and sitting in their cars were more likely to die of heart disease than those who sat for 11 hours a week or less,even if they exercised.

One possible mechanism, demonstrated in animal studies, is that being sedentary may affect lipid metabolism (油脂代谢). Prolonged inactivity appears to sharply reduce the activity of an important enzyme (酶) called lipoprotein lipaseo which is responsible for breaking down circulating blood lipids and them available to muscles for energy, Dr. Stamatakis said. Exercise has very little impact on the enzyme’s activity, he said. Extended sitting may also lead to high levels of low-grade inflammation (炎症) ,which can also lead to heart disease,Dr. Stamatakis said. The study focused on recreational screen time because it’s the easiest to cut down,Dr. Stamatakis said. But he encouraged employees who work at computers all day to get up and take breaks and short walks periodically.