An American study has recently revealed one of the most enduring mysteries of our human existence: why do women generally live longer than men? According to the results, the answer is genetic, but also hormonal.
According to the latest data from the Centers for Disease Control and Prevention (CDC), life expectancy in the United States is 76 years for men, and 81 years for women. A difference that is sometimes explained by the way of life: the food, the consumption of alcohol or tobacco. Yet this trend is also the same in animals. Researchers at the University of California, San Francisco, tried to find out if there was a scientific explanation. Their study, published in the journal Aging Cells, explains that the answer lies in our chromosomes.
It’s better to have XX chromosomes
To carry out this study, the researchers genetically modified mice, and divided them into four groups. In the first, they had XX chromosomes, the female chromosomes, with developed ovaries. In the second, they had XY chromosomes, male chromosomes, and testes. Finally, in the last two groups, the rodents had either XX chromosomes and testes, or XY chromosomes and ovaries.
In the Y chromosomes there is a gene, called the “SRY” gene, that determines the masculine traits. It is by moving this gene that the researchers managed to grow testicles in mice with XX chromosomes. They found that all mice with XX chromosomes tended to live longer than others, whether they had ovaries or testicles.
Hormones play a role
However, life expectancy was really longer when mice had XX chromosomes and ovaries, such as women. “This suggests that hormones produced by the ovaries increase the lifespan of mice with two X chromosomes, either by influencing mouse development or by activating certain biological pathways during their lifetime,” says Dr. Dena Dubal, lead author of the study.
It remains to be seen now how to have two X chromosomes increases life expectancy. What role does this second chromosome play? Previously, other studies have shown that in women, there is in each cell an X chromosome that is randomly disabled. Thus, if the active chromosome is damaged, the other can reactivate and take over. Women therefore seem to be the winners of this genetic hazard.