We know that exercise improves our overall health, and that it specifically lowers the risk of diseases such as heart disease, stroke, type 2 diabetes, and osteoporosis. But a study published in a recent issue of The New England Journal of Medicine suggests that your level of physical fitness is the strongest predictor of death from any cause.

About the study

Researchers at Stanford University and the Veterans Affairs Health Care System studied 6213 men (average age 59) who were referred by their doctors for exercise testing. The exercise test consisted of exercising on a treadmill while hooked up to an electrocardiogram (ECG)—a machine that monitors the heart's activity. At the time of the test, each man also completed a questionnaire about his medical history, current medications, and risk factors for various diseases.

During the exercise test, blood pressure, heart rate, and exercise capacity were monitored and abnormal results on the ECG were recorded. Based on their medical records and the results of their exercise tests, the men were classified as either having cardiovascular disease or not.

In July 2000, after an average of 6 years of follow-up, the researchers used the Social Security Death Index to determine which of the men had died, although they were unable to ascertain the cause of death. Then they compared the exercise capacity of the men who had died with the exercise capacity of the men who were still living.

The findings

Men with the lowest exercise capacity according to the treadmill test were more than 4 times more likely to die than men with the highest exercise capacity. This was true regardless of whether the men had cardiovascular disease, which implies that exercise may even offset the risks associated with cardiovascular disease. Overall, as exercise capacity increased the chances of survival increased.

After adjusting the calculations for age (which affects your chances of dying), poor exercise capacity was the strongest predictor of death in men, regardless of their cardiovascular status. Exercise capacity even outranked smoking and history of chronic diseases as strong predictors of death.

There are limitations to this study, however. First, all the study subjects were men, so it's not clear how these results apply to women. Second, exercise capacity was measured via performance on a treadmill test rather than by measuring peak oxygen consumption, which is a more accurate measure of exercise tolerance. Third, the specific cause of death for each man is not known, so we don't know if exercise affects the risk of certain causes of death, but not others.

How does this affect you?

Does this mean you need to start (or keep) exercising? Absolutely. This study provides evidence that physical fitness may be even more important for good health and longevity than had previously been estimated. The findings don't provide evidence of a causal relationship between exercise capacity and mortality, but it does confirm the findings of numerous other studies indicating that exercise is essential for good health and can help ward off any number of diseases.

How often do you need to exercise? National health and exercise organizations recommend you do moderately intense physical activity for at least 30 minutes on most (preferably all) days of the week. Since brisk walking qualifies as moderately intense physical activity, that's a place to start if you're new to exercise.

If you find the idea of a regular exercise program daunting, consider making an appointment with a certified athletic trainer, either at a local gym or through referral from your health care provider or a friend. Make sure this person understands your goals and can help you maintain an exercise program that you'll enjoy and stick with.

It doesn't take long to begin reaping the rewards of regular exercise. According to the American College of Sports Medicine, regular exercise can improve your fitness by 15% to 30% in just three to six months.