DEAR DOCTOR K: I believe you when you say that regular exercise protects my health. But I'm just 20. For me the question is, when should I begin regular exercise? The diseases that exercise protects against usually don't develop until a person is older than 60. I'd like not to have to worry about exercise for a few decades.
DEAR READER: I wish I could rid you of that worry. But, in fact, if you are not already exercising regularly, you are probably putting your health at risk 30 years from now. Many of the diseases that exercise protects against actually start in young adulthood and take decades to become severe enough to cause symptoms. For example, autopsy studies have been performed on soldiers killed in war -- people your age. They reveal that many already have early signs of atherosclerosis, the cause of heart attacks, strokes and premature death.