Globally, on average women live about 5% longer than men. Males and females generally have the same system. Same organs, same respiratory system, same circulatory system… However, they have a single difference—the difference in their reproductive system. One might assume that this small change would only impact reproduction. However, thanks to the body's smallest and largest cells: sperm and eggs, crucial to human reproduction, women tend to outlive men. For the first time in vertebrates, scientists in Japan have demonstrated that the cells developing into eggs in females and sperm in males contribute to sex differences in lifespan. Removing these cells results in animals with equal life expectancies. One of the most prominent scientists experimenting, Prof. Tohru Ishitani explained “The aging process in killifish is similar to that in humans” meaning, this thrilling finding could solve one of the biggest problems of mankind, Aging.
The researchers examined aging in the turquoise killifish, a small, fast-growing freshwater fish with a lifespan of only a few months. Killfish are genetically close to human beings sharing about 70% of our coding DNA meaning their aging process could be similar to humans. As in humans, female killifish live longer than males. “We expected that germ cell removal would extend the lifespan of both males and females, but it extends only male lifespan and shortens female lifespan,” Ishitani said. “It was unexpected, but we realized that this discovery may shed light on sex differences in lifespan.” When the researchers removed the germ cells from these fish, they found that males and females had similar lifespans. “After removing the germ cells, male killifish lived longer than usual, and female lifespans became shorter,” explains lead author Kota Abe. “We wanted to understand how germ cells could affect males and females so differently. “Our next step was to investigate the factors responsible.”
The team found that hormonal signaling was very different in females than in males. Hormone signaling monitors growth, development, metabolism, reproduction, mood, and many other physiological functions meaning they are essential parts of our bodies. Female killifish without germ cells had significantly less estrogen signaling (Estrogen contributes to cognitive health, bone health, the function of the cardiovascular system, and other essential bodily processes.), which can shorten lifespan by increasing cardiovascular disease risk and decrease overall life quality. The females also had significantly more growth factor signaling (insulin-like growth factor 1). This made the females grow larger while also suppressing signals within the body important for maintaining health and slowing aging. On the contrary, male killifish without germ cells had improved muscle, skin, and bone health. The scientists found that these fish had increased amounts of a substance that activates vitamin D, as well as evidence of vitamin D signaling in their muscles and skin.
The team’s results pointed to the possibility that vitamin D can improve duration, leading them to test whether a vitamin D supplement could increase the lifespan of the fish. The team went on to test whether giving killifish vitamin D extended lifespan and discovered increases of 21% in males and 7% in females. While no ill effects were seen, Ishitani said it was important to use the “appropriate amount”. In the UK, health officials recommend a daily 10 microgram or 400 IU vitamin D supplement in the autumn and winter. When they administered vitamin D, they found that the lifespans of both males and females were significantly extended, suggesting that vitamin D signaling provides health benefits throughout the body. The senior author Tohru Ishitani explains “Our work suggests that vitamin D signaling could influence the longevity of other vertebrates, including humans.”
Ultimately, Whether sperm suppresses men's life expectancy is unclear, but there is supporting evidence. For instance, a 2012 study of 81 Korean eunuchs found they lived 14 to 19 years longer than non-castrated (An uncastrated man or male animal has not had its testicles ) men of similar socioeconomic backgrounds. However, the records from the 16th to the 19th century make it difficult to exclude other factors. "In this study, removing sperm or egg precursor cells resulted in shorter lifespans for females but extended lifespans for males, likely due to increased vitamin D activity," Clancy said. "This indicates that the signaling from these cells, which modulates lifespan, differs between sexes in these fish and likely in other animals as well." The discovery that germ cells affect male and female longevity in opposing ways is an important clue in unraveling the mysterious interactions between reproduction, aging, and lifespan. It’s unclear exactly how vitamin D fits into this puzzle, but it could be part of a future where we humans could live longer than one could imagine.