Previous studies have suggested that when it comes to using aspirin as a preventative for heart attacks, it is less effective in women than in men.
However, according to a new study the apparent lower efficacy in women is not due to a failure of aspirin to reduce platelet clumping or aggregation, as was thought.
Lead researcher Diane M. Becker M.P.H., Sc.D., a professor at the Johns Hopkins University School of Medicine and Bloomberg School of Public Health, says women are clearly benefiting from taking aspirin and should continue to take it to improve their cardiovascular health.
Dr. Becker says aspirin has been proven by all previous studies to lower the risk of stroke and, as their latest findings show, it also reduces platelet aggregation that can lead to potentially fatal clots in blood vessels.
In order to understand why aspirin appeared to have different effects in men and women, Becker and her team studied the effects of 14 days of aspirin therapy on elements in the blood involved in clotting, called platelets.
More than 500 men and 700 women took part in the study, called the Genetic Study of Aspirin Responsiveness (GeneSTAR) which was carried out at Hopkins from June 2004 to November 2005.
The study enrolled participants from across the country who ranged in age from 21 to 80; 31 percent were black and the rest were white.
None had previous histories of heart problems, such as a heart attack, but all were considered to be at slightly increased risk of heart disease because of a family history.
Fifty percent of women participants were postmenopausal.
Blood testing was conducted both before and after treatment and in total, more than 200 different tests of platelet reactivity were performed and analyzed in the study.
Because whole blood contains other cells that affect platelet aggregation, testing was repeated using a purified version of test samples made up of strictly platelet-rich plasma.
At the start of the experiment, laboratory tests of blood platelets in women were found to be four times more likely than in men to aggregate when exposed to arachidonic acid, a clot-inducing chemical in the pathway that is most suppressed by aspirin.
While taking aspirin, participants maintained a strict and consistent diet and exercise regimen, with no smoking or consumption of foods that by themselves affect platelet activity, such as caffeine, chocolate, wine or grapefruit juice.
Physical examinations and pill counts were conducted to ensure that all participants adhered to the study protocol and because aspirin reaches its maximal effect in the body at five days, the researchers say a longer study testing period was not required to determine the drug's effects on platelet function.
The team found that by taking aspirin daily for a two-week period, both men and women blocked key biological pathways that lead to platelet clumping.
Dr. Nauder Faraday a platelet biologist and study co-author, says the results show that aspirin does what it is supposed to do in both men and women, but further research is required to get a definitive answer as to who really benefits from aspirin and under what circumstances it works and does not work, and how dosage should be worked out.
The research is published in the Journal of the American Medical Association March 22/29, 2006.