Emphasize Sex in Research, orders National Institutes of Health

Reproducibility in biological research — or more specifically the lack of it — is an ongoing issue.

While experiments may be published even in a top scientific journal, other researchers who attempt to repeat the same experiments under the same conditions often find contradicting results. As a measure of this, a recent study attempted to reproduce psychology publications and successfully replicated only 39 out of 100 studies.

It turns out that excluding sex in experimental design may have contributed to reproducibility issues. Furthermore, sex can also have a biological impact on our scientific understanding and influence how well early biological studies translate into advances in human medicine.

“Sex is there from nature,” said T. Michael Gill, PhD, and head of the animal Behavioral Core at Gladstone Institutes in an interview. “I think it should always be considered given that we’re not a unisex mammal.”

To address such issues, last May, the National Institutes of Health (NIH) released a directive for future grant applications that’s meant to increase the reliability and reproducibility of experiments. One of the four variables that the NIH emphasized was a consideration of all biological variables, including sex.

Sex, as opposed to the social construct of gender, is defined by characteristics encoded in the DNA such as organs and hormonal differences.

Per the NIH directive, the consideration of sex would be necessary for human studies as well as animal and cellular studies.

Including sex will also help researchers better understand the impact of differences that come with each sex.

“There are plenty of differences – both at an inherent biologic level and there are many differences at a behavior level as well,” said Gill.

Most obviously clear differences in hormones and anatomy exist between sexes. But also more subtle behavioral differences have been distinguished such as in aggression in male and female mice.

How will these changes affect researchers, including those who do not work in humans? Primarily, biology researchers will need to increase their n’s — including higher numbers of animals tested — to perform experiments in both sexes with the same rigor.

However, not all studies will need to be performed in both sexes if there is an underlying scientific reasoning for examining only one. For example, studies looking at breast cancer or prostate cancer could still be performed in only one sex.

As Gill said, “the overarching goal is actually to produce beneficial effects on the human condition.”

Hopefully, including sex as a consideration in the design of future studies will produce both more reproducible data and importantly aid advancements in human health.