The push to encourage women to enter STEM fields has become so ubiquitous that there are op-eds written seemingly every week, a dedicated page on the White House website, and even a line of interactive dolls. A lesser-known gender discrepancy in science, however, is the lack of female research subjects. Despite a 1993 law requiring women and minorities to be included as subjects in clinical research funded by the National Institutes of Health, women continue to be under-represented.
Of course, clinical trials (testing medical interventions on human subjects) are only a small subset of medical studies. Other types of research that inform health care practices are conducted on animals and cells, and those studies, researchers at Northwestern University say, are also vulnerable to sex bias.
The results are especially alarming for female-prevalent disorders like thyroid and cardiovascular disease—only 12 percent of these studies included female subjects.
In a new study published in September's issue of Surgery, vascular surgeon Melina R. Kibbe and her colleagues examine studies from 2011 to 2012 from the top five general surgery journals. They found a total of 618 publications using animals and/or cells.
Of those studies, 32 percent did not report the sex of animals or cells at all. Among those that did, 80 percent of publications studied only males, 17 percent had only females, and three percent included both sexes.
Of that three percent (13 papers total), only seven of them separated data by sex.
Cell-based papers were far less likely to indicate the sex of subjects (76 percent) compared with animal-based papers (22 percent). International papers were more likely to state the sex of subjects (80 percent) than American papers (53 percent), though international studies reported even higher levels of male-only research.
Why is there such a bias? Kibbe and her colleagues write that including both sexes for animal/cell subjects can be expensive. And, female subjects may add unwanted variability due to hormonal changes. Still, including female subjects is essential because a growing body of research shows that “women manifest, progress, and react differently than men” when it comes to disease response.
The results are especially alarming for female-prevalent disorders like thyroid and cardiovascular disease—only 12 percent of these studies included female subjects. While there is “robust and surmounting evidence” that women’s experience with heart disease differs from men’s, less than 25 percent of research on the topic includes consideration of sex. This has immediate, scary implications: “Even as mortality [from cardiovascular disease] has decreased in most counties in the United States from 1992 to 2006, female mortality increased in 42.8 percent of these counties.”
The researchers hope this study will be a wake-up call for the scientific community, including practicing physicians, who are often naïve when it comes to gender differences in treatment plans, as well as researchers. Since the completion of this study, the editors of each of the top five surgical journals have agreed to change their author guidelines to require indication of the sex of animals or cells used, and a written justification if researchers do not include both sexes.
"We believe that industry should set the example for sex equality in research," the authors conclude. "This approach will impact positively the delivery of health care to both men and women."