Low Proportion of Women in Clinical Trials

August 1, 2008

A review of three-and-a-half decades of clinical cardiology trials shows that while an increasing number of women are being included in clinical trials, their numbers are still so low in some areas of research that it's questionable whether study conclusions can be legitimately applied to women.

Investigators from the Duke Clinical Research Institute, led by Chiara Melloni M.H.S. '07, a research associate and cardiologist, reported the finding at the annual meeting of the American College of Cardiology this past spring.

The researchers examined the numbers of women included in 156 randomized clinical trials cited by the American Heart Association's 2007 guidelines for cardiovascular disease prevention in women.

They found that, overall, women constituted 30.6 percent of the total number of participants enrolled, with the percentage growing significantly over the past thirty-six years. In 1970, women made up only 9 percent of those registered in the prevention trials. In 2006, that figure rose to 42.4 percent, although researchers say the latter figure reflects a striking increase in the number of single-sex trials aimed solely at women.

The researchers found that the location of the trials appeared to play a role in participation: More women were enrolled in clinical trials in the U.S. (45 percent) compared with those abroad (26 percent).

Clinical conditions appeared to make a difference, too, with the highest number of women found in trials for hypertension (41 percent), diabetes (39 percent), and stroke (37 percent), and the lowest for trials related to heart failure (29 percent), coronary artery disease (24 percent), and high cholesterol (17 percent).

The funding source for the studies did not seem to have any influence on the numbers of women involved. Women made up about 30 percent of all participants enrolled in both government and privately funded trials.

"It's heartening to note some gain in the numbers of women taking part in cardiovascular disease prevention trials, but we are still seeing substantial deficits in female representation in many areas of research," says Kristin Newby, an associate professor of medicine and senior author of the study.

"The results of this study tell us that efforts to change that picture are not robust enough to make a difference and that we still have a lot of work to do to ensure that we can generate evidence-based, sex-specific treatment recommendations when they are appropriate."