Probably as a result of the protective effect of estrogen, heart disease occurs in women 10 to 15 years later than it does in men. While many women over 45 take statins, some might have a low risk for cardiovascular disease. And being at low risk might make the risks of taking statins outweigh the benefits.
Understanding the benefits of statins for women at low risk hasn't been clear-cut. Some large studies on statin drugs have included significantly fewer women than men, and in some cases trial results were not initially broken down by gender. But analyses have looked at data from women without heart disease across a number of large trials. A study in the Journal of the American Medical Association found that in women without cardiovascular disease, the effect of statin therapy was not clear because of the relatively small number of events. But statin use did not appear to have a beneficial effect on "total mortality" for women with or without previous cardiovascular disease. (In other words, they did not—in general—live longer as a result of taking the drug.)
And a 2008 meta-analysis in the International Journal of Cardiology found that for both men and women without heart disease, using a statin appeared to have no effect on total mortality during the period of the trials (2.8 to 5.3 years). Another meta-analysis from the Archives of Internal Medicine from June 2010 had a similar finding: Even high-risk men and women without prior cardiovascular disease who took a statin did not appear to live longer during the trial years (an average of 3.7 years) than those who didn't take one.
One way to determine the benefit of treatment is to calculate the "number needed to treat"—how many people need to take the drug for so many years before one event—such as a heart attack, for example—is avoided. The U.K. study mentioned earlier calculated that for women at "medium" risk of cardiovascular disease, 44 would need to take a statin for five years to prevent one case of it. And the previously mentioned JAMA analysis estimated that 140 women who don't have cardiovascular disease would need to be treated to prevent one coronary heart disease event, such as a heart attack.
An exception to these findings has been a large-scale trial of men and women without high LDL cholesterol but who had elevated levels of a substance that indicates inflammation is present in the body, C-reactive protein. In the trial, called JUPITER ("Justification for the Use of Statins in Prevention: an Intervention Trial Evaluating Rosuvastatin"), apparently healthy men and women were found to have significantly reduced rates of a first major cardiovascular event and death from any cause when taking rosuvastatin. (See our related story about this trial here.)