Women live longer than men in every country in the world. In 2021, global life expectancy was 73.8 years for women and 68.4 years for men, according to Our World in Data. That is a gap of about five years.
The size of the gap changes from country to country. In Russia, Belarus and Ukraine it was more than ten years in 2021. In Nigeria it was under two. That spread shows that biology sets part of the gap and the way people live sets the rest.
Here is what the research says about both.
The Gap Begins at Birth
Boys are more likely than girls to be born prematurely, and they have higher death rates in their first year of life. Researchers think genetics explains part of this. Boys carry one X chromosome, so a faulty gene on that X has no backup copy. Girls carry two X chromosomes, so a second copy of each gene is available.
A Second X Chromosome May Protect Women
The X chromosome holds hundreds of genes, and many of them are involved in brain function and immunity. In women, one X is mostly switched off in each cell, but scientists now think the second copy still does useful work.
A team at UCSF tested this in mice bred so that sex chromosomes and sex organs could be studied separately. Mice with two X chromosomes lived longer than mice with an X and a Y, and this held true in mice with ovaries and in mice with testes. The longest-lived group had two X chromosomes and ovaries, which suggests chromosomes and hormones work together.
In 2025, the same research group reported that the “silent” X chromosome switches some of its genes back on in the brains of older female mice. One of those genes, PLP1, helps build the insulation around nerve fibres. When the researchers raised PLP1 levels in older mice, both males and females performed better on learning and memory tests. This work was done in mice, and the team is still studying if the same process happens in older women.
Hormones Shape the Immune System
Sex hormones influence how the immune system responds to threats. Women generally mount stronger immune responses to infections and vaccines than men, according to a widely cited review in Nature Reviews Immunology. A stronger response helps clear infections faster. It also helps explain why autoimmune conditions are more common in women.
Women Have Slightly Longer Telomeres
Telomeres are protective caps on the ends of chromosomes, and they shorten each time a cell divides. A meta-analysis covering more than 36,000 people found that women have slightly longer telomeres than men on average. The difference was small and appeared consistently with only one measurement method, so researchers treat it as one part of the explanation and not the main cause.
The Pattern Appears Across the Animal Kingdom
Researchers at the Max Planck Institute for Evolutionary Anthropology compared lifespans across 1,176 species of mammals and birds in a study published in 2025. Female mammals lived about 12% longer than males on average. In birds the pattern reversed, and males lived about 5% longer.
This matters because the chromosome setup also reverses in birds. Female birds carry two different sex chromosomes, while males carry two matching ones. The results support the idea that two matching sex chromosomes offer some protection.
The team also found bigger lifespan gaps in species where males compete hard for mates, which links shorter male lives to the energy spent on that competition. The gaps shrank in zoos, where animals get regular food and vet care, but they rarely disappeared.
Behaviour Explains a Large Share
Biology does not explain the whole gap. The World Health Organization reports that a 30-year-old man has a 44% higher chance than a woman of the same age of dying from a non-communicable disease before 70. The same report notes that men often seek health care less than women when they have the same disease.
Researchers point to a few habits that have widened the gap over the last century:
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Men have historically smoked more than women, and the gap narrowed as smoking rates fell.
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Men drink more alcohol and use more drugs on average.
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Men more often work in jobs with higher physical risk.
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Men see a doctor less often, so health problems are found later.
Heart disease is the clearest example. Ischaemic heart disease is one of the biggest causes of early death in men worldwide, according to a 2024 study in The Lancet Public Health.
Living Longer Is Not the Same as Living Well
The same Lancet study found a second pattern. Men carry more of the burden from conditions that cause early death. Women carry more of the burden from conditions that affect daily life without being fatal, with low back pain at the top of the list, followed by headache disorders.
Researchers call this the health-survival paradox. Women live longer, but they also spend more of their lives in poor health. For women, the goal is to keep those extra years active and comfortable. For men, the goal is to reach those years at all.
What Everyone Can Take From This
The research points to a few habits that help both sexes:
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Stop smoking, or never start, since smoking explains a large share of the gap over the last century.
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Book regular check-ups, especially for heart health, even when you feel well.
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Build strength and keep moving, because your muscles and joints decide how independent you stay in later life.
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Keep alcohol moderate and protect your sleep.
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See a doctor early when something changes, instead of waiting for it to get worse.
Your chromosomes are fixed, but most of the factors on this list are within your control.
Ageless NMN
Genes, hormones and habits all shape how long you live, and one more factor works inside every cell: NAD+. Your cells use NAD+ to turn food into energy and to run their daily repair work. A study of human skin samples found that NAD+ levels fall with age in both men and women.
Ageless NMN gives your body NMN, a direct building block it uses to make NAD+, to support cellular energy and healthy ageing for women and men alike. Add it to your morning routine alongside the habits above.
