It’s been a long-standing tradition that most medical studies have focused only on Caucasian males because researchers feared that hormonal differences in women would skew the findings. The problem is, that approach ignores how various diseases and medications can affect the sexes differently.

Without distinguishing between the sexes, research would not have revealed that heart disease, for example, affects men and women differently…or that certain drugs, such as the widely prescribed sleeping pill zolpidem (Ambien), are metabolized at different rates, potentially affecting dosage recommendations.

After the shortcomings of sex-biased medical research began to receive more attention, researchers set out in 2009 to see whether more women were finally being represented in medical studies. The results were disappointing—only 28% of the studies reviewed that year included women.

As concerns grew around biased medical research methods, the National Institutes of Health (NIH), the largest public funder of clinical trials in the US, implemented a 2016 policy requiring researchers to consider sex as a biological variable, which involves comparing research results between men and women.

Latest development: To find out whether more females are now being represented in medical studies, a team of researchers conducted a 10-year follow-up on sex-biased research by looking at a body of scientific literature published in 2019. The meta-analysis, which was published in eLife, included studies that focused on both laboratory animals and humans in clinical research.

In the review, researchers looked at more than 700 studies that covered nine biological fields. The results were a mixed bag. While the number of studies that included females grew from 28% in 2009 to 49% a decade later, there was no increase in the number of studies that broke down the findings by sex. In fact, in the field of pharmacology, the percentage of research that included female sex as a biological variable fell from 33% to 29%.

Meanwhile, approximately one-third of the studies that included both male and female subjects did not quantify the sample size by sex. This practice occurred most often in the fields of neuroscience, immunology and general biology—the same areas that showed the greatest increases in the use of female study participants.

Takeaway: When sex differences are ignored in medical research, the development of effective disease prevention and treatment strategies for all individuals is significantly hampered. For this reason, the authors of the follow-up meta-analysis call on medical researchers to provide a rationale for not including women in future studies. Along with that, the study authors encourage journal publishers and medical schools, universities and institutions that give research grants to advocate against sex-biased research.

Source: Study titled “Meta-Research: A 10-Year Follow-Up Study of Sex Inclusion in the Biological Sciences,” by researchers at Feinberg School of Medicine, Northwestern University, Chicago, and Smith College, Northampton, Massachusetts, published in eLife.