In a commentary published this week in the journal Nature and featured in the New York Times, NIH Director Dr. Francis Collins unveiled new NIH policies that will require balanced inclusion of male and female cells and animals in NIH-funded preclinical research (with few defined exceptions). Though inclusion of women in NIH-funded clinical trials has improved to the point where about half of all research participants are women, preclinical research lags in achieving a sex balance. One reason cited for the continued predominance of male models in preclinical research is researchers’ concerns about effects of the estrous cycle on research findings; however, the current situation may also simply reflect the inertia of years of laboratory conventions. Described as a “blind spot” in preclinical research, the lack of adequate inclusion of female models is troubling, given the numerous examples of sex differences in areas including cell physiology, drug metabolism, and adverse drug effects.

“Inadequate inclusion of female cells and animals in experiments and inadequate analysis of data by sex may well contribute to the troubling rise of irreproducibility in preclinical biomedical research, which the NIH is now actively working to address.”

The new NIH policies will begin with a staggered rollout starting in October 2014. The policies will be supplemented by other NIH efforts such as training, partnerships with publishers to encourage publication of sex analyses, and a program launched in 2013 that extends supplemental funding to existing research to increase sex comparisons.

The Nature commentary was co-authored by Janine A. Clayton, MD, director of the Office of Research on Women’s Health and associate director for Research on Women’s Health for the NIH.