Women live longer than men.
This simple statement holds a tantalizing riddle that Steven Austad, Ph.D., and Kathleen Fischer, Ph.D., of the University of Alabama at Birmingham explore in a perspective piece published in Cell Metabolism.
“Humans are the only species in which one sex is known to have a ubiquitous survival advantage,” the UAB 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.”
Though other species, from roundworms and fruit flies to a spectrum of mammals, show lifespan differences that may favor one sex in certain studies, contradictory studies with different diets, mating patterns or environmental conditions often flip that advantage to the other sex. With humans, however, it appears to be all females all the time.
“We don’t know why women live longer,” said Austad, distinguished professor and chair of the UAB Department of Biology in the UAB College of Arts and Sciences. “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, which 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,” write Austad and Fischer, a research assistant professor of biology.
- 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, Austad and Fischer say. 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,” they write. “Yet in every year, regardless of food availability or pestilence, women at the beginning of life and near its end survived better than men.”
- 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,” they write. “For one cause, stroke, there was no sex bias, and for one other, Alzheimer’s disease, women were more at risk.”