A recent monitoring study suggests that women’s body temperatures are no more variable than men’s, despite menstrual cycles and hormonal variability. The analysis, published in the journal Biology of Sex Differences, casts doubt on an idea that has long colored biomedical research – that ovarian cycles make females unsuited for drug trials and other clinical experiments.

That claim – along with gender discrimination and other factors – is thought to fuel women’s ongoing underrepresentation in such trials, which continues despite a concerted effort by the federal government and researchers to bolster sex-specific research.

When researchers looked at six months’ worth of continuous body temperature data from a group of males and females, they found that despite sex differences in body temperature, neither group was more variable.

The researchers examined temperature data from a pool of age-matched 20-to-79-year-olds: 300 females and 300 males. The participants were part of a broader University of California study, TemPredict, designed to track vital signs and help predict the onset of coronavirus symptoms.

Over six months, patients wore an Oura ring, a wearable “smart ring” that monitors heart rate, respiration, body temperature, and movement. (Oura Health Oy, the Finnish technology company that produces the ring, was one of the study’s funders.)

When the scientists delved into the body temperature data, comparing it across sex and over time and looking for excessive variability or measurement errors among females, they did find sex differences. Women with menstrual cycles showed temperature fluctuations across a roughly 28-day cycle, confirming that ovarian rhythms do affect body temperature.


However those differences did not confound or sully the data, and the researchers note that the predictability of the women’s temperature variability made their temperatures easier to predict than men’s.

“In this study, the difference between two men is bigger than the difference between the average man and the average woman,” Lauryn Keeler Bruce, the paper’s first author and a Ph.D. student in the Bioinformatics and Systems Biology program at UC San Diego, said in a news release. “In addition, the variability between men and women is not statistically significant.”

Temperatures cycled along with sleep and wake patterns and time of day for both sexes.

Because no one group consistently proved more variable, the researchers concluded that women’s temperature data is no more unreliable than men’s.

“These findings contradict the viewpoint that human females are too variable across menstrual cycles to include in biomedical research,” the researchers write. Pregnancy or sex-specific cancers might create larger effects, they note. But that’s no reason to exclude women from medical research, they conclude: “Females still need to be more routinely included in the research, and we find no statistical evidence that doing so would negatively affect study power.”

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