Worldwide, there are presently 31 people over the age of 110. Of these, 30 are women. According to the Morbidity-Mortality Paradox or Health Paradox, despite higher rates of disability and poorer health than men, women experience greater longevity in modern human societies. Everywhere in the world women live longer than men; but this was not always the case. The available data from rich countries shows that women did not live longer than men in the 19th century.
Why do women live so much longer than men today, and why has this advantage increased over time? The evidence is limited and we have only partial answers. We know that biological, behavioral and environmental factors all contribute to the fact that women live longer than men; but we don’t know exactly how strong the relative contribution of each of these factors is.
According to the World Health Statistics report of 2021, globally, women can expect to live an average five years longer than men, but when it comes to healthy life expectancy, that advantage shrinks to less than half as much at 2.4 years. Females in India can expect on average to live almost three years longer than males. But when it comes to living a healthy life, the difference almost vanishes. This pattern of large gender differences results in higher life expectancy but much smaller in healthy life expectancy is not unique to India. Public health experts say this phenomenon could be due to poorer access to the healthcare and attention to health, especially among older women. In Singapore, women can expect to live four years longer than men.
One major physiological factor is that women suffer less oxidative stress, says Dr Kayser Mamun, Senior Consultant at the Department of Geriatric Medicine, Singapore General Hospital (SGH), a member of the Sing Health group. Oxidative stress generates free radicals. “Some scientists believe that free radicals can lead to cell damage, which is one of the underlying mechanism of ageing,” explains Dr Mamun. Oxidative damage is four times higher in men than women, possibly due to lower oestrogen levels,” says Dr Mamun. The female hormone oestrogen has other protective effects. Oestrogen raises good cholesterol (HDL) and lowers bad cholesterol levels, thus reducing the women’s risk of developing stroke and heart disease – and dying in the prime of their lives. Conversely, the male hormone testosterone raises bad cholesterol (LDL) and reduces good cholesterol (HDL), exposing men to a higher risk of getting stroke or heart disease at a younger age than women.
Independently of the exact weight, we know that at least part of the reason why women live so much longer than men today, but not in the past, has to do with the fact that some key non-biological factors have changed over time. What are these changed factors? Some are well known and relatively straightforward. One of the factors that affect longevity in men is that they are more likely to be seen with a cigarette hanging out of their mouths – according to the World Health Organization (WHO), 40% of men are smokers compared to 9% of women. Also, fewer women tend to abuse alcohol compared to men. Some studies have also found that women are more likely to see a doctor when they are sick. An 85-year-old psychologist Katharine Esty, who interviewed 128 people in their eighties for her book “Eightysomethings,” found that aging women tend to put in more effort to stay healthy, while “men will still eat steak and order French fries.”
Other reasons are more complicated like that in rich countries the female advantage increased in part because infectious diseases used to affect women disproportionately a century ago, so advances in medicine that reduced the long-term health burden from infectious diseases, especially for survivors, ended up raising women’s longevity disproportionately. Scientists confirm that these habits make men more prone to chronic obstructive pulmonary disease (COPD), lung cancer, coronary heart disease, digestive problems, and liver disease. Studies have also shown that compared to women, men are at a higher risk of developing diabetes and it’s complications like diabetic nephropathy and diabetic foot.
In another research, after observing the blood of men and women between the ages of 65 and 95, Nir Barzilai, Director of the Institute for Aging Research at the Albert Einstein College of Medicine, found men’s protein levels changed at higher rates than women’s did. According to the study, men’s protein levels experienced 600 significant changes, compared with 277 significant changes for women, indicating that “female biology seems to be more stable than men’s,” Barzilai said. Separately, Michael Ullman, a neuroscience professor at Georgetown University, has found that a person’s sex might influence declarative memory, or the ability to recall things such as specific events or where someone left his or her car keys. According to one study by Ullman, both men and women scored comparably on a memory test involving image recollection—until age 70, when a “significant female advantage emerged.” Ullman also found that the positive effects of education on memory ability were more pronounced in women than men. “The sex difference was really striking,” he said.
Women have oestrogen in their corner. Scientists have shown that testosterone may stimulate the prostate gland and increase the risk of prostate cancer. Also, studies have shown that testosterone improves reproductive function earlier in life but shortens the lifespan in the long run (antagonistic pleiotropy effect). Other than maintaining female sexual organs, oestrogen helps in blood clotting, increases the level of good cholesterol and maintains gastrointestinal tract. It also has antioxidant properties and helps delay the decrease of skin collagen in women as they grow older. Scientists believe that because of estrogen’s protective effect, premenopausal women are less likely to have coronary heart disease than men and women who have hit menopause.
But perhaps the true reason lies in the testosterone that drives most other male characteristics, from deeper voices and hairier chests to balding crowns. Evidence comes from an unexpected place: the Imperial Court of the Chosun Dynasty in Korea. Korean scientist Han-Nam Park recently analyzed the detailed records of court life from the 19th Century, including information about 81 eunuchs whose testicles had been removed before puberty. His analyses revealed that the eunuchs lived for around 70 years as compared to an average of just 50 years among the other men in the court. Overall, they were 130 times more likely to celebrate their hundredth birthday than the average man living in Korea at the time. Although not all studies of other types of eunuch have shown such pronounced differences, overall it seems that people (and animals) without testicles do live longer.
Not only do women escape the risks of testosterone – they may also benefit from their own “elixir of youth” that helps heal some of the ravages of time. The female sex hormone estrogen is an “antioxidant” meaning that it mops up poisonous chemicals that cause cells stress. In animal experiments, females lacking oestrogen tend not to live so long as those who have not been operated on – the exact opposite of the male eunuch’s fate. “If you remove a rodents’ ovaries, then the cells don’t repair against molecular damage quite as well,” says Kirkwood.
The exact reasons are elusive, but David Gems at University College London speculates that the damage may be done by the end of puberty. For speculative evidence, he points to the sad cases of mental health patients, institutionalized in the USA in the early 20th Century. A few were forcibly castrated as part of their “treatment”. Like the Korean eunuchs, they too lived for longer than the average inmate – but only if they had been sterilized before the age of 15. Testosterone might make our bodies stronger in the short-term, but the same changes also leave us open to heart disease, infections, and cancer later in life. “For example, testosterone might increase seminal fluid production but promote prostate cancer; or it might alter cardiovascular function in a way that improves performance early in life but leads to hypertension and atherosclerosis later,” says Gem.
Another reason is that girls are more robust from the moment they are born. Some scientists believe that girls are more robust, stronger and healthier, than boys from birth itself. Joy Lawn, director of the Centre for Maternal, Reproductive, and Child Health at the London School of Hygiene and Tropical Medicine, has said that whenever a newborn boy comes into the neonatal unit, statistically, he is more likely to die compared to a girl. The extra X chromosome in the female DNA is somehow said to be responsible for this. Human DNA is made up of at least two sex chromosomes that decide the gender. Females have XX, whereas males have XY.
Recently, research was done on two sets of mice: one with natural male-female mouse biology (XX and XY) and the other set with XX chromosomes paired with testes and XY chromosomes paired with ovaries. A senior author of the study and neurologist, Dena Dubal, found that mice with two X-chromosomes outlived all the mice but the ones with testes and XX chromosome also turned out to live longer. This longevity effect was observed after 21 months, as it is considered to be the end of a normal mouse’s lifespan. The researchers concluded that the second X and its genetic expression has a protective effect that increases survival. That difference may subtly alter the way that cells age. Having two X chromosomes, women keep double copies of every gene, meaning they have a spare if one is faulty. Men don’t have that back-up. The result is that more cells may begin to malfunction with time, putting men at greater risk of disease.
The evidence shows that differences in chromosomes and hormones between men and women affect longevity. For example, males tend to have more fat surrounding the organs (they have more ‘visceral fat’) whereas women tend to have more fat sitting directly under the skin (‘subcutaneous fat’). This difference is determined both by oestrogen and the presence of the second X chromosome in females; and it matters for longevity because fat surrounding the organs predicts cardiovascular disease. But biological differences can only be part of the story – otherwise we’d not see such large differences across countries and over time. Although we donot have a definitive answer, but we do have some clues. A 2018 study by Adriana Lleras-Muney and Claudia Goldin, looking at long-run data on infectious diseases, gives us insights into this mechanism. Lleras-Muney and Goldin show that in the US, infectious diseases disproportionately affected females between the ages of 5 and 25 in the 19th century, so as the burden of infectious disease fell for both men and women, it disproportionately helped women.
We know that the longer lifespan of females is common in other animals, but it is not universal. We also know that biological, behavioral and environmental factors all contribute to the fact that women live longer than men; but we don’t know exactly how strong the relative contribution of each of these factors is. In most countries for all the primary causes of death the mortality rates are higher for men. More detailed data shows that this is true at all ages; yet paradoxically, while women have lower mortality rates throughout their life, they also often have higher rates of physical illness, more disability days, more doctor visits, and hospital stays than men do. It seems women do not live longer than men only because they age more slowly, but also because they are more robust when they get sick at any age. This is an interesting point that still needs more research.
Research has also found that a woman’s heart rate increases during the menstrual cycle, offering the same benefits as moderate exercise. Among the other alternatives is the “jogging female heart” hypothesis – the idea that a woman’s heart rate increases during the second half of the menstrual cycle, offering the same benefits as moderate exercise. The result is delayed risk of cardiovascular disease later in life. Or it could also be a simple matter of size. Taller people have more cells in their bodies, meaning they are more likely to develop harmful mutations; bigger bodies also burn more energy, which could add to wear and tear within the tissues themselves. Since men tend to be taller than women, they suffer more long-term damage.
Once the children are born, the men are more disposable. Kirkwood and Gem both think of this as a kind of evolutionary pay-off that gave both men and women the best chances of passing on their genes. During mating, women would be more likely to go for alpha males, pumped up on testosterone. But once the children are born, the men are more disposable, says Kirkwood. “The welfare of offspring is intimately connected with welfare of the maternal body. The bottom line is that it matters more for the children that the mother’s body should be in good shape, rather than the father’s.” That is cold comfort for men today. As it is, the scientists admit that we need to keep on looking for a definitive answer. “We really have to retain an open mind as to how much the difference can be explained by hormonal differences and other factors,” says Kirkwood. But the hope is that eventually, the knowledge may provide some hints to help us all live a little longer.
The author retired as Director General of Income Tax (Investigation), Chandigarh. He runs an NGO – The Tree Club and is Trustee of Vitasta Health Care Trust, a charitable heath centre.