Can hormones explain why women live longer on average than men?

Men have shorter telomeres on average, the protective caps at the ends of chromosomes. This goes hand in hand with a shorter lifespan, but whether telomere length is the cause or a consequence of ageing remains unclear. In some animal species, males actually live longer, which shows that this relationship is not universal.

Oestrogens, the female sex hormones, play a role in the immune system, but that role is two-sided. Depending on the situation, they suppress inflammation or actually promote it. Women respond more strongly to viral infections: they produce more antibodies and maintain lower levels of inflammation, probably in part because they have two X-chromosomes. Those same factors, however, also increase the risk of autoimmune diseases, in which the immune system attacks the body itself. That downside counts too.

Around the menopause, sex hormones decline rapidly. Combined with normal cellular ageing, this increases the likelihood of stress dysregulation in the brain and, with it, of neuropsychiatric conditions at older ages. The higher risk of Alzheimer's disease in women is also linked to this: nearly two thirds of Alzheimer's patients are women. Part of that difference stems from the fact that women live an average of 4.5 years longer, since advanced age is the strongest risk factor. But there is also evidence of female-specific biological mechanisms that independently raise the risk.

Hormones therefore do not explain everything. Social and cultural factors, such as risk-taking behaviour, working conditions and attention to health, also contribute to the difference in lifespan. Moreover, the hormonal protection is not one-sidedly beneficial: greater survival chances during infections stand opposite greater vulnerability to autoimmune diseases and, after the menopause, to brain conditions. In short, sex hormones and sex-linked genetics likely contribute to women's longer lifespan, but they are not a complete explanation.