U.S-NIH Policy on Sex as a Biological Variable: Progress and Gaps

Bridging the Gap in Sex-Inclusive Research

The U.S-NIH introduced the Sex as a Biological Variable (SABV) policy in 2016 to improve the rigor and reproducibility of biomedical research. By requiring investigators to consider sex in study design and analysis, the policy aims to ensure that findings are relevant to both men and women.

A recent review of 574 U.S.-NIH R01-funded publications (2017–2024) shows encouraging progress but also highlights persistent shortcomings. About 61% of studies included both sexes, with human-subject research more likely to do so than animal studies. However, fewer than half (44%) of these studies actually analyzed results by sex, leaving important differences unexplored.

Interestingly, author gender appears to play a role. Articles with women as first authors conducted sex-based analyses more often (50% vs. 39%), and studies led by women in both first and last author positions were twice as likely to analyze data by sex compared to male-led teams. This suggests that diversity in research leadership may influence how rigorously SABV principles are applied.

The study also found that animal research lags behind human studies in sex inclusion and analysis, underscoring the need for stronger enforcement in preclinical work. Only 4% of articles provided a clear rationale for single-sex studies or the absence of sex-based analyses, pointing to a lack of transparency in methodological decisions.

While the SABV policy has increased awareness and inclusion, the gap between including both sexes and analyzing differences remains significant. Without sex-based analyses, biomedical research risks overlooking crucial insights into disease mechanisms, treatment responses, and health outcomes.

The findings emphasize the importance of clearer guidance, stronger incentives, and broader adoption of reporting standards such as the SAGER guidelines. By fully integrating SABV into research practices, the scientific community can ensure that discoveries benefit everyone and advance healthcare equity.