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Researchers realized decades ago that high blood pressure is a cardiovascular danger signal. They don't understand the exact mechanism yet, but physicians think elevated pressure puts a strain on blood vessels, causing them to tear or develop weak areas where plaque can gain an easy foothold. Hypertension (to use the technical term) can also force small blood vessels to burst like an overstressed garden hose; if that happens in the brain, it's called a stroke--the other major cardiovascular killer besides heart attack.
Medication can help with the most severe cases of hypertension, but the first line of defense, physicians agree, is to cut back on a substance that has been shown over and over to keep blood pressure high: sodium, especially in the form of salt.
If cutting back on salt is good for people with hypertension, it should logically be good for everyone else too. It may be, but dueling studies released three years ago demonstrate that the case is far from airtight. Scientists writing in the British Medical Journal concluded that reducing salt intake reduces blood pressure in all people, even those who are not hypertensive. But a study published the very same week in the Journal of the American Medical Association argued that people with normal blood pressure got no significant benefit from salt reduction.
Which one was right? Probably neither, since both studies were flawed. The J.A.M.A. study included subjects who were on low-salt diets for a very short time--perhaps too short for any effect to be noticed. And the BMJ study could not effectively measure the influence of other factors that could have made a difference. Those who ate less salt may also have watched what they ate in general, for example, exercised more or been less overweight.
The truth is that the question of what ordinary people should do about salt has simply not been settled yet. That doesn't mean we should throw up our hands in despair. Even without hard scientific proof, says Dr. Theodore Kotchen of the Medical College of Wisconsin, keeping sodium levels down is probably a good idea--particularly since there is no evidence that a low-sodium diet is harmful. The one exception: people who are losing salt through heavy perspiration during exercise or hard physical work. Reducing salt intake in the middle of a heat wave can actually be dangerous to your health.
Physical exertion is another area in which doctors have been sending mixed signals. As far back as 1953, studies showed that people who got more exercise had fewer heart attacks. The physiological explanation has come more slowly, but one reason is simply that the heart is a muscle; frequent workouts keep it strong.
Another factor, doctors believe, is that exercise holds down blood pressure. When the heart pumps blood more quickly through the body, vessels dilate--or widen--to accommodate the extra flow. The overall effect is to lower pressure throughout the cardiovascular system. People who get regular exercise have about a 30% lower risk of developing heart-threatening hypertension than people who don't.