The Grapevine

Why Gender Equality Matters In Aging Studies: 4 Of 5 Compounds Increase Lifespan Only In One Sex

Dr. Nancy Nadon, a lead scientist at the National Institutes of Aging, explains the importance of using female mice alongside males in experiments. La Tarte au Citron, CC by 2.0

In 1993, Congress required the National Institutes of Health to include women in any funded research involving human subjects, while last year in June, Congress extended this "gender equality" to lab rats. With the introduction of the Research for All Act, congressional supporters plan to ensure the NIH use both male and female lab animals, tissues, and cells in all biomedical research. Dr. Nancy Nadon, lead scientist at the National Institutes of Aging’s Intervention Testing Program, explained the importance of using female mice alongside males in experiments of compounds meant to extend lifespan.

While including animals of both sexes is simply “very good science,” as she comments in a recent video, an experiment's potential consequences offer the most compelling reasons why. “For the most part, what we’ve seen is quite a big difference between the response in males and females,” she says.

Specifically, when testing drugs that might increase lifespan, NIA-funded researchers saw an effect in only one sex or another in four out of five compounds. Unusually, aspirin, which is commonly used as a blood thinner to prevent heart attacks in both men and women, was one such compound. “Here we had a result that indicated at least for our outcome measurement, lifespan, there was a big difference,” Nadon said. “For males, there was a positive effect, for females, there wasn’t any.”

Another drug the NIA has high hopes for — rapamycin, originally developed as an anti-rejection drug for patients undergoing kidney transplants — showed more complicated gender-effects. Rapamycin has been shown to extend the lives of mice by more than 10 percent. However, while the result from “rapamycin was positive in both males and females, the effect at lower dose was much more robust in females,” according to Nadon.

While most of us non-scientists most likely jump to the conclusion that it’s a matter of metabolism — females and males absorb and process drugs differently due to differences in weight, muscle, and hormones — this isn’t the case. The NIA’s experiments suggest the possible explanation may be much more complicated, much more deep. “There’s likely to be many different ways the sex difference is likely to be manifested at the molecular and cellular level,” said Nadon. For this reason any biological study must consider both sexes to be most accurate.

Rapamycin continues to be tested and the video below explains some of the many scientific hopes invested in this drug. However, prepare to be surprised. The experiments of these researchers at the University of Washington range far beyond the usual rodents, coming much closer to home: