Women tend to live longer than men, and the key may be in the protective effects estrogen has on chromosomes, new research suggests.
One of our best gauges of longevity is the length of telomeres, the set of genetic information at the tips of chromosomes.
Women's telomeres tend to be longer than men's and to stay that way for longer, though exactly why telomere-length is associated with longer lifespans.
Now, new research from the University of California, San Francisco, suggests that estrogen actually stokes the activity of an enzyme that helps to lengthen telomeres and may extend lifespans.
On average, women life about five percent longer than men throughout the world, though the gender gap varies significantly from country to country.
Experts have blamed this on all manner of environmental differences through the years: men are more likely to drink and smoke more and are at greater risk of developing heart disease.
One recent analysis suggested that that gap will close by 2032, as rates of smoking and drinking fall and level out for the two genders.
But scientists have also observed that differences in life expectancy mat be coded into the genetics of men and women.
They have found a close link between the length of a person's telomeres and the length of their life.
Our DNA is encoded in 23 pairs of chromosomes and telomeres are the end caps of those chromosomes.
Telomeres are made of the same nucleic acid bases as the rest of human genetic information but their job is a protective one.
They keep the precious genetic material in the rest of the chromosome from getting damaged, especially as cells replicate.
Replication after replication over time starts to wear down telomemeres. When eventually they become too short to be functional, cells start malfunctioning, in part because their DNA is exposed, so to speak.
Without telomeres, cells start to age and die, so these simple end-caps are vital to our health, and also good measures of our overall health and potential longevity.
It's not just time, but trauma that ages telomeres.
Stress, health problems and poor habits all also wear on telomeres, and, in turn, on our life spans.
American life expectancy fell for the second year in a row in 2018, and the gap between men's and women's life expectancies has grown to five years.
Women now live to an average age of 81.1, while men only live to be 76.1 years old.
Their telomeres reflect this.
And the new research from the University of California, San Francisco, suggests that the estrogen might be the secret.
The female hormone that gives women their feminine appearances, menstrual cycles, and fertility, may also help to give them longer lives.
Estrogen fuels some cancers, but has long been known to have protective effects against other diseases. Higher levels of the hormone are thought to help keep the cardiovascular system in good working order and promote healthier bones.
The new research, presented today at the North American Menopause Society annual meeting in San Diego, adds to the list of good things estrogen does the possibility of protecting telomeres.
Lead study author Dr Elissa Epel said: 'Some experimental studies suggest estrogen exposure increases the activity of telomerase, the enzyme that can protect and elongate telomeres.'
If this is in fact the case, maintaining estrogen levels may become more important to women as they reach menopause and their hormone levels fall.