It is a well-known statistical fact that women have a longer lifespan than men — not just in the United States, but across the world. What is less well-known is that this difference applies across most the animal kingdom as well.
Although no satisfactory explanation has been offered to explain this phenomenon, a new study by researchers at the University of California, San Francisco (USCF), has started to shed light on the issue. The results of their research appear in the journal Aging Cell.
Genetically, women have two X chromosomes, while men have one X chromosome and one Y chromosome. X chromosomes are rich in genetic material, containing hundreds of protein-encoding genes. Y chromosomes, for the most part, simply carry the gene that determines male traits.
According to Dr. Dena Dubal, a professor of neurology at UCSF and co-author of the study: “One can imagine nature has driven females to evolve this way. When you’re living longer, you can really ensure the well-being of your offspring and maybe even their offspring.”
In order to understand the mechanisms that cause female longevity to be greater than male longevity, Dr. Dubal and her research team genetically engineered mice into one of four categories.
Two control groups:
- Mice with an XX chromosome combination and female hormones.
- Mice with an XY chromosome combination and male hormones.
And two experimental groups:
- Mice with an XX chromosome combination and male hormones.
- Mice with an XY chromosome combination and female hormones.
The researchers showed that all the mice with an XX chromosome profile survived longer, on average, than mice with an XY chromosome profile — regardless of whether they had male or female hormones. Yet, when it came to statistically analyzing which mice survived the longest, the mice with an XX chromosome profile and female hormones were the clear winners.
The researchers concluded that both genetic and hormonal factors play a fundamental role in aging and longevity. In the words of Dr. Dubal: “This suggests that the hormones produced by female gonads increase lifespan in mice with two X chromosomes, either by influencing how the mouse develops or by activating certain biological pathways during their lives.”
When analyzing and comparing the four groups of mice, the researchers noticed that the XX chromosome profile — even with male hormones — was sufficient to protect these mice from an early death.
The researchers noted that although they don’t yet understand why the second X chromosome decreases mortality, there are other studies that offer some clues.
In normal females, one X chromosome in every cell is deactivated. This ensures that if the currently active X chromosome becomes damaged or destroyed, the deactivated X chromosome can be reactivated and take the place of the damaged cell. As explained above, X chromosomes are rich in protein-encoding genes. Thus, the ability to replace a damaged X chromosome may play a fundamental role in longevity.
As Dr. Dubal explains it, “When things go wrong in aging, having more of the X chromosome, along with its diversity of expression could be extremely beneficial.”
More research is required to confirm this hypothesis, as well as to explain the extra longevity boost provided by female hormones.
The takeaway for us is somewhat mixed: it appears to be fortunate, in terms of longevity, to be female. If you are a man, there is not too much you can do about it, except be happy for your wife.
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