Aspirin, first developed as a painkiller almost a century ago, is still viewed by many as a miracle drug. While rarely prescribed for pain, aspirin's major use is its effect on platelets.

Aspirin prevents the formation in platelets of a molecule called thromboxane A2 that is essential for normal platelet aggregation. Platelets play a central role in stopping bleeding by first attaching to a bleeding wound, then aggregating together to form a plug. Coagulated plasma and red cells combine with the platelet plug to form a blood clot.

While essential to stop bleeding, platelets can cause harm by aggregating in a blood vessel damaged by the deposition of cholesterol. This leads to a clot that either partially or completely blocks a blood vessel. This can occur in many areas of the body but is most serious when a coronary or cerebral artery is blocked, leading to a heart attack or stroke.

Studies in recent years indicate that taking as little as a baby aspirin (81 milligram) daily can interfere with platelet function sufficiently to prevent platelets from aggregating and reduce the risk of heart attack or stroke.

Aspirin has other benefits, according to a study published in the journal Lancet. The study tracked more than 25,000 subjects taking aspirin for at least 20 years. The research suggested that aspirin decreases the risk of lung cancer by 30 percent, colon cancer by 40 percent and esophageal cancer by as much as 60 percent. The National Cancer Institute reports that aspirin may protect against breast and prostate cancer. Most experts believe that by inhibiting certain enzymes, aspirin decreases inflammation that in turn reduces the chance of cells transforming and becoming cancerous.

Based on these observations, many health-care providers recommend that all adults take an 81-milligram aspirin daily in the hope of preventing heart attacks, strokes and cancer. Using a medication to prevent an illness in otherwise healthy and asymptomatic individuals is referred to as primary prevention.

To be effective, there must be a proven benefit that outweighs any potential side effects. Good examples of primary prevention are the addition of fluoride to water to reduce the risk of tooth decay and cavities as well as the fortification of flour and cereals with iron to reduce the risk of anemia due to iron deficiency. Thanks to these preventive public-health approaches, tooth decay and iron deficiency have become quite rare. And in these two examples, the adverse effects are insignificant enough to make the approach valuable.

But is primary prevention of using aspirin worthwhile? First, it must significantly lower the risk of disease, and second, it should have virtually no risk. Unfortunately, research just published in the Archives of Internal Medicine showed that aspirin does not reduce the risk of death from heart attack, stroke or cancer in otherwise healthy people.

In this study, more than 100,000 healthy subjects with no risk factors of vascular disease were divided into two groups, either receiving aspirin or a placebo. After a follow-up period of six years, there were 1,500 nonfatal and 500 fatal heart attacks and an equal number of fatal and nonfatal strokes. The only benefit of aspirin was a 10 percent reduction in the number of nonfatal heart attacks. Particularly worrisome was a 31 percent increase in the risk of life-threatening bleeding from the stomach.

Now experts are saying that healthy people should not take aspirin, as the side effects lead to more problems than they prevent. Its use in the prevention of cancer is now also in question.

This does not mean that aspirin should no longer be prescribed for anyone. The information is watertight that aspirin prevents second heart attacks and strokes. Aspirin should also be used in people at high risk of disease, including anybody over the age of 60, smokers and those with diabetes, high blood pressure, elevated cholesterol or proven evidence of vascular disease. Using aspirin to prevent illness in such people is referred to as secondary prevention and its use in those with disease and illness is referred to as tertiary prevention.

Always consult your physician before starting or stopping any treatment including aspirin. Be aware of the risk factors of heart disease and stroke and if needed, aspirin still remains a valuable and effective medication in high-risk individuals.

Dr. David Lipschitz is the author of the book "Breaking the Rules of Aging." To find out more about Dr. David Lipschitz and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate Web page at www.creators.com. More information is available at:

www.drdavidhealth.com