(January 17, 2008 - Insidermedicine) Being resistant to the blood thinning effects of aspirin may be associated with an increased risk for heart attack and stroke, according to research published in the British Medical Journal.

Here are some facts about aspirin and cardiovascular health:

•    Many heart attacks and strokes are caused by a clot forming in the circulating blood and becoming lodged in the blood vessels feeding the heart or in the brain.

•    Aspirin has what is called an antiplatelet effect – a blood thinning property that make the blood less "sticky" and likely to form clots.

•    Many individuals who are known to be at high risk for heart attack and stroke are prescribed a low dose of aspirin to take every day to help keep the blood from forming clots, but some individuals are resistant to the antiplatelet effects of aspirin.

Canadian researchers reviewed the data from 20 studies looking at the effects of aspirin on cardiovascular health. Nearly 3,000 patients were included in these studies, all of whom had cardiovascular disease and had been prescribed aspirin to help prevent the development of heart attack or stroke.

Overall, 28% of the patients in the studies were classified as being resistant to the antiplatelet effects of aspirin. These aspirin resistant patients were more likely to suffer a heart attack or stroke or even to die than those who were sensitive to aspirin. In fact, 39% of aspirin resistant patients experienced a cardiovascular event, compared to only 16% of those who were not resistant.

The authors recommend that more research be conducted on understanding and identifying aspirin resistance, and that physicians take the possibility of aspirin resistance into account before they prescribe it.

For Insidermedicine in Depth, I'm Dr. Susan Sharma.