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 on June 14.
"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:
Austad first became interested in the topic when Georgetown University asked him to lecture on it in 2003. Although lab models like the roundworm C. elegans, the fruit fly Drosophila melanogaster and the mouse Mus musculus are intensively used in scientific studies, people in those fields are not very aware of how longevity patterns by sex can vary according to genetic backgrounds, or by differences in diet, housing or mating conditions, Austad says.
Those uncontrolled variables lead to different results in longevity research. A survey of 118 studies of laboratory mice by Austad and colleagues in 2011 found that 65 studies reported that males outlived females, 51 found that females outlived males, and two showed no sex difference.
But if variables are carefully controlled, mice may prove to be a useful model to study sex differences in the cellular and molecular physiology of aging, Austad and Fischer write.
This understanding will be helpful as researchers start to develop drugs for human use that affect aging, Austad says. "We may be able to develop better approaches," he said. "There is some complicated biology underlying sex differences that we need to work on."
Differences may be due to hormones, perhaps as early as the surge in testosterone during male sexual differentiation in the uterus. Longevity may also relate to immune system differences, responses to oxidative stress, mitochondrial fitness or even the fact that men have one X chromosome (and one Y), while women have two X chromosomes.
But the female advantage has a thorn.
"One of the most puzzling aspects of human sex difference biology," write Austad and Fischer, "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.
"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."
Austad first became interested in the topic when Georgetown University asked him to lecture on it in 2003. Although lab models like the roundworm C. elegans, the fruit fly Drosophila melanogaster and the mouse Mus musculus are intensively used in scientific studies, people in those fields are not very aware of how longevity patterns by sex can vary according to genetic backgrounds, or by differences in diet, housing or mating conditions, Austad says.
Those uncontrolled variables lead to different results in longevity research. A survey of 118 studies of laboratory mice by Austad and colleagues in 2011 found that 65 studies reported that males outlived females, 51 found that females outlived males, and two showed no sex difference.
But if variables are carefully controlled, mice may prove to be a useful model to study sex differences in the cellular and molecular physiology of aging, Austad and Fischer write.
This understanding will be helpful as researchers start to develop drugs for human use that affect aging, Austad says. "We may be able to develop better approaches," he said. "There is some complicated biology underlying sex differences that we need to work on."
Differences may be due to hormones, perhaps as early as the surge in testosterone during male sexual differentiation in the uterus. Longevity may also relate to immune system differences, responses to oxidative stress, mitochondrial fitness or even the fact that men have one X chromosome (and one Y), while women have two X chromosomes.
But the female advantage has a thorn.
"One of the most puzzling aspects of human sex difference biology," write Austad and Fischer, "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.
Story Source:
Materials provided by University of Alabama at Birmingham. Original written by Jeff Hansen. Note: Content may be edited for style and length.
Hey men, there’s good news and bad news.
The good news is we’re living decades longer than we were just a couple centuries ago.
The bad news is the gap between how long men live and how long women live is still about the same.
An international team of researchers published a study on Monday in the Proceedings of the National Academy of Sciences.
In it, they detailed the great strides that humans have made in longevity the past 200 years, even compared to other primates such as monkeys and apes.
However, they noted, women are still outliving men by about five years, the same gap that was present in the early 1800s.
That gap between male and female lifespans is also found in other primate species.
Materials provided by University of Alabama at Birmingham. Original written by Jeff Hansen. Note: Content may be edited for style and length.
Hey men, there’s good news and bad news.
The good news is we’re living decades longer than we were just a couple centuries ago.
The bad news is the gap between how long men live and how long women live is still about the same.
An international team of researchers published a study on Monday in the Proceedings of the National Academy of Sciences.
In it, they detailed the great strides that humans have made in longevity the past 200 years, even compared to other primates such as monkeys and apes.
However, they noted, women are still outliving men by about five years, the same gap that was present in the early 1800s.
That gap between male and female lifespans is also found in other primate species.
And researchers aren’t entirely sure why.
"It's puzzling. If we can make life last so long, why can't we shrink the male-female gap?" study co-author Susan Alberts, a biology professor at Duke University, said in a press release.
Read more: Men and women’s hearts age differently »
The study included people from industrialized countries, people born before the Industrial Age, and modern hunter-gathers.
They compared the human data with lifespan records from six species of wild primates that have been studied from three to five decades.
The researchers said the data shows humans are making more rapid gains in longevity than other species on the primate family tree.
For example, the life expectancy for people in Sweden has jumped from the mid-30s in the early 1800s to more than 80 years today. That’s more than double in a 200-year span.
"It's puzzling. If we can make life last so long, why can't we shrink the male-female gap?" study co-author Susan Alberts, a biology professor at Duke University, said in a press release.
Read more: Men and women’s hearts age differently »
Rapid lifespan growth
The researchers from the United States, Germany, Denmark, Canada, and Kenya compiled the birth and death records of more than 1 million people from the 1700s to the present.The study included people from industrialized countries, people born before the Industrial Age, and modern hunter-gathers.
They compared the human data with lifespan records from six species of wild primates that have been studied from three to five decades.
The researchers said the data shows humans are making more rapid gains in longevity than other species on the primate family tree.
For example, the life expectancy for people in Sweden has jumped from the mid-30s in the early 1800s to more than 80 years today. That’s more than double in a 200-year span.
Researchers attribute the leap in lifespans to modern
medicine and public health facilities. In particular, they note, childbirth deaths
and childhood diseases have been greatly reduced.
"We've made a bigger journey in lengthening our lifespan over the last few hundred years than we did over millions of years of evolutionary history," Alberts said.
However, the gap between men and women hasn’t changed much.
Worldwide, the average lifespan is about 71 years. Men, though, live an average of 68 years while women live an average of 73 years.
In the United States, the average lifespan is almost 79 years. Men live on average about 76 years while woman live an average of 81 years.
Researchers said a similar proportional gap exists between females and males in almost every wild primate population they studied.
Read more: Women pay more for healthcare services than men »
They surmise it might lie in the X chromosome. Women have two of them while men only have one.
The solitary X chromosome in men may not be enough to compensate for any gene variants in that single chromosome.
"We've made a bigger journey in lengthening our lifespan over the last few hundred years than we did over millions of years of evolutionary history," Alberts said.
However, the gap between men and women hasn’t changed much.
Worldwide, the average lifespan is about 71 years. Men, though, live an average of 68 years while women live an average of 73 years.
In the United States, the average lifespan is almost 79 years. Men live on average about 76 years while woman live an average of 81 years.
Researchers said a similar proportional gap exists between females and males in almost every wild primate population they studied.
Read more: Women pay more for healthcare services than men »
Genetics, behavior, or both?
Alberts and the other researchers say there is probably a genetic component to the gap in male and female longevity.They surmise it might lie in the X chromosome. Women have two of them while men only have one.
The solitary X chromosome in men may not be enough to compensate for any gene variants in that single chromosome.
Alberts said that wars and other aggressive behavior by men
may also be a factor.
However, Dr. Jamin Brahmbhatt, a urology surgeon at The PUR Clinic at Orlando Health’s South Lake Hospital in Florida, thinks there may be more to it than that.
Brahmbhatt told Healthline a big factor may be that men simply don’t take care of themselves as well as women do.
They don’t eat as well and they don’t go to the doctor nearly as often as women do.
“Men simply don’t prioritize their health,” Brahmbhatt said.
The surgeon believes that this behavior may have its roots in childbirth.
He said women usually go through pregnancy in the first few decades of their life. They develop a pattern early of going to the doctor and taking care of their health.
Most men don’t do that until they are perhaps beyond 50 or 60 years of age.
Brahmbhatt said there is only so much you can do about genetics, but there is a lot you can do about behavior.
“You have to live with the cards you are dealt, but there are things around you that you can control,” he said.
However, Dr. Jamin Brahmbhatt, a urology surgeon at The PUR Clinic at Orlando Health’s South Lake Hospital in Florida, thinks there may be more to it than that.
Brahmbhatt told Healthline a big factor may be that men simply don’t take care of themselves as well as women do.
They don’t eat as well and they don’t go to the doctor nearly as often as women do.
“Men simply don’t prioritize their health,” Brahmbhatt said.
The surgeon believes that this behavior may have its roots in childbirth.
He said women usually go through pregnancy in the first few decades of their life. They develop a pattern early of going to the doctor and taking care of their health.
Most men don’t do that until they are perhaps beyond 50 or 60 years of age.
Brahmbhatt said there is only so much you can do about genetics, but there is a lot you can do about behavior.
“You have to live with the cards you are dealt, but there are things around you that you can control,” he said.
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