Women live about five years longer than men worldwide, with an average life expectancy of 75.0 years compared to 70.1 years for men across 183 countries. This gap has persisted across cultures and centuries, which points to a combination of deep biological advantages and behavioral patterns rather than any single explanation.
Estrogen Protects the Heart for Decades
Cardiovascular disease is the leading killer globally, and women have a built-in shield against it for much of their lives. Estrogen promotes the release of nitric oxide in blood vessel walls, a molecule that relaxes arteries and keeps blood pressure lower. It also reduces cholesterol levels and limits cholesterol buildup inside artery walls. These effects work through multiple pathways simultaneously, acting on both the smooth muscle cells in arteries and the cells lining them.
This protection is substantial. Premenopausal women have significantly lower rates of heart attack and stroke than men of the same age. Once menopause arrives and estrogen levels drop, women’s cardiovascular risk begins to climb, but the decades of protection still leave them with a net advantage. Men, by contrast, face rising cardiovascular risk from their 30s onward with no comparable hormonal buffer.
Two X Chromosomes as a Genetic Safety Net
Women carry two X chromosomes while men carry one X and one Y. This matters because the X chromosome contains roughly 800 protein-coding genes, and some of those genes are essential for immune function, brain maintenance, and cellular repair. When men inherit a harmful mutation on their single X chromosome, they have no backup copy. Women can typically rely on the healthy version from their other X chromosome to compensate.
There’s an additional wrinkle that makes this even more interesting. In female cells, one X chromosome is normally silenced to balance gene expression between the sexes. But research published in Science Advances found that certain genes on the “silent” X escape this inactivation, especially in brain tissue during aging. This means women can get a double dose of specific X-linked genes that influence cognitive resilience and neural function. The finding may help explain why women show greater resistance to cognitive decline in early Alzheimer’s disease.
Women’s Immune Systems Age More Slowly
The immune system deteriorates with age in everyone, but it deteriorates faster in men. Studies comparing healthy volunteers from their 20s through their 90s found that women were less affected by the age-related decline in several key immune cell populations. Women maintained higher counts of naive T cells (the immune cells that respond to new threats), B cells (which produce antibodies), and a healthier ratio of helper to killer immune cells.
A study of a Japanese population ranging from age 20 to 90 confirmed this pattern: females were consistently less susceptible to age-related immune changes. Men, meanwhile, showed steeper drops in critical immune cell types. On top of this slower decline, men develop more pronounced chronic low-grade inflammation as they age, a process sometimes called “inflammaging.” This background inflammation accelerates tissue damage and contributes to heart disease, cancer, and neurodegeneration. While both sexes experience it, genetic analysis suggests the inflammatory genes become more active in men, potentially accounting for the higher inflammation levels observed in aging males.
The Mother’s Curse Hypothesis
Mitochondria, the structures inside cells that generate energy, carry their own small set of DNA. This DNA is inherited exclusively from mothers. Because natural selection can only “see” mitochondrial mutations through their effects on females (since only females pass them on), mutations that are harmful to males but neutral in females can persist in the population unchecked. This idea, known as the Mother’s Curse hypothesis, suggests that mitochondrial function may be evolutionarily optimized for female biology.
Mitochondrial DNA is especially vulnerable to accumulating harmful mutations because it lacks the repair mechanisms and genetic reshuffling that protect the DNA in cell nuclei. Over a lifetime, these small inefficiencies in male mitochondrial function could contribute to faster cellular aging and greater susceptibility to age-related diseases. Researchers have invoked this hypothesis as one explanation for the near-universal pattern of females outliving males across mammalian species, not just in humans.
Telomeres Shorten Faster in Men
Telomeres are the protective caps on the ends of chromosomes, and their length serves as a rough biological clock. Shorter telomeres are associated with aging and age-related disease. Data from the U.S. National Health and Nutrition Examination Survey showed that men’s telomeres shorten at a significantly faster rate than women’s. After adjusting for ethnicity, physical activity, and existing health conditions, the rate of telomere decline in men was about 20% steeper than in women.
Women’s telomere loss also followed a less steady pattern, with sharper declines in their 20s and 50s but periods of relative stability in between. Men showed a more consistent, grinding loss across all age groups. Estrogen may play a role here too, as it appears to activate telomerase, the enzyme that helps maintain telomere length.
Behavioral Risks Hit Men Harder
Biology doesn’t explain the entire gap. Men are far more likely to die from external causes like accidents, homicide, and suicide. In years of potential life lost (a measure that weights deaths at younger ages more heavily), men lost roughly five times as many years to external causes as women: 5,297 per 100,000 compared to 1,106 for women.
Workplace fatalities paint a stark picture. Since 2011, men have accounted for 91% to 93% of all fatal occupational injuries every year. This isn’t just because more men work. Men are overwhelmingly concentrated in goods-producing industries like construction, mining, and manufacturing, where 31% of male injury cases occur, compared to under 9% for women. Testosterone likely plays a role in the risk-taking behavior that contributes to accidental deaths, though research shows testosterone levels don’t predict differences in accidental death rates between individual men.
Men Avoid the Doctor
Women are more likely to seek medical care, and they do it sooner. Survey data shows that when sick, about 59% of women sought treatment from a healthcare practitioner compared to 53% of men. Men were also more likely to self-medicate or simply ignore symptoms. This pattern holds across nearly all types of health concerns, including mental health.
The reasons are partly cultural. Traditional masculinity norms discourage men from appearing vulnerable or admitting to health problems, leading many to delay care until conditions become severe. Preventive care, the kind that catches cancer, diabetes, and heart disease early enough to treat effectively, is underused by men across virtually every population studied. The cumulative effect of skipping screenings and postponing treatment adds years to the mortality gap that biology alone would create.
Testosterone’s Complicated Role
Testosterone is often cast as the villain in male longevity, but the reality is more nuanced. A large study tracking men over time found that lower testosterone levels were actually associated with higher mortality from heart disease, cancer, stroke, pneumonia, and Alzheimer’s disease. This held true across most disease categories in both age-dependent and age-independent ways.
Where testosterone does appear to shorten male lives is through behavior rather than direct physiological harm. The same hormone linked to risk-taking, aggression, and competitive behavior contributes to the higher rates of accidental death and violence that disproportionately affect men, particularly younger men. So testosterone simultaneously protects men against certain diseases while pushing them toward dangerous situations. The net effect still tilts toward shorter lives.