Humans are the only species in which one sex is known to have a ubiquitous survival advantage, Steven Austad, Ph.D., and Kathleen Fischer, Ph.D., of the University of Alabama at Birmingham researchers write in their research review covering a multitude of species. Indeed, the sex difference in longevity may be one of the most robust features of human biology. We don’t know why women live longer, it’s amazing that it hasn’t become a stronger focus of research in human biology.
Evidence of the longer lifespans for women includes:
The Human Mortality Database: this database has complete lifespan tables for men and women from 38 countries that go back as far as 1751 for Sweden and 1816 for France. Given this high data quality, it is impressive that for all 38 countries for every year in the database, female life expectancy at birth exceeds male life expectancy.
A lifelong advantage: Longer female survival expectancy is seen across the lifespan, at early life (birth to 5 years old) and at age 50. It is also seen at the end of life, where Gerontology Research Group data for the oldest of the old show that women make up 90 percent of the supercentenarians, those who live to 110 years of age or longer.
The birth cohorts from the mid-1800s to the early 1900s for Iceland. This small, genetically homogenous country which was beset by catastrophes such as famine, flooding, volcanic eruptions and disease epidemics provides a particularly vivid example of female survival. Over that time, life expectancy at birth fell to as low as 21 years during catastrophes and rose to as high as 69 years during good times. Yet in every year, regardless of food availability or pestilence, women at the beginning of life and near its end survived better than men.
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Resistance to most of the major causes of death. Of the 15 top causes of death in the United States in 2013, women died at a lower age-adjusted rate of 13 of them, including all of the top six causes. For one cause, stroke, there was no sex bias, and for one other, Alzheimer’s disease, women were more at risk.
But the female advantage has a thorn.
One of the most puzzling aspects of human sex difference biology, something that has no known equivalent in other species, is that for all their robustness relative to men in terms of survival, women on average appear to be in poorer health than men through adult life.
This higher prevalence of physical limitations in later life is seen not only in Western societies, they say, but also for women in Bangladesh, China, Egypt, Guatemala, India, Indonesia, Jamaica, Malaysia, Mexico, the Philippines, Thailand and Tunisia.
One intriguing explanation for this mortality-morbidity paradox is a possible connection with health problems that appear in later life. Women are more prone to joint and bone problems, such as osteoarthritis, osteoporosis and back pain, than are men. Back and joint pain tends to be more severe in women, and this could mean chronic sleep deprivation and stress. Thus, the sex differences in morbidity could be due to connective tissue maladies in women, and connective tissue in humans is known to respond to female sex hormones.
But this is just one of several plausible hypotheses for the mystery of why women live longer, on average, than men.
All of which seems like an unstoppable force pushing us towards death but several lines of evidence suggest there are brakes that can slow its progress. For instance, a common diabetes drug, metformin, can modestly slow ageing in mice. And simply changing one gene involved in cell metabolism in a roundworm can lead it to live many times longer than its parents; while it is unlikely the same changes would help more complex organisms, it hints that ageing is not beyond our control. Ageing is a surprisingly plastic process that can be manipulated, de Magalhaes says.