MadSci Network: Medicine

Re: Why do women live longer than men? Is this true of most species?

Date: Wed Sep 15 14:06:12 1999
Posted By: Linda J. Weyandt MD/CRNA, Grad student, Psychology/, North Central University
Area of science: Medicine
ID: 935461426.Me

I believe this will answer your question and provided you with additional

Thank you for your question.

Why Women Live Longer than Men
Women around the world have a survival advantage over men--sometimes by as
much as 10 years. What gives them the upper hand?

by Thomas T. Perls, M.D., M.P.H
Harvard Medical School

Ruth C. Fretts, M.D., M.P.H.
Harvard Medical School

Image: JW Stewart
Hormones, genetics and the fact that women go through menopause may explain
why women live longer than men on average.

It is a fact of life that men enjoy certain physical advantages over women.
On average, men are stronger, taller, faster and less likely to be
overweight. But none of these attributes seem to matter over the long haul.
For whatever the physical virtues of maleness, longevity is not among them.
Women, as a group, live longer than men. In all developed countries and 
undeveloped ones, women outlive men, sometimes by a margin of as much as 10
years. In the U.S., life expectancy at birth is about 79 years for women 
about 72 years for men. The gender discrepancy is most pronounced in the
very old: among centenarians worldwide, women outnumber men nine to one. 
gender gap has widened in this century as gains in female life expectancy 
have exceeded those for males.

The death rates for women are lower than those for men at all ages--even
before birth. Although boys start life with some numerical leverage--about
115 males are conceived for every 100 females--their numbers are
preferentially whittled down thereafter. Just 104 boys are born for every
100 girls because of the disproportionate rate of spontaneous abortions,
stillbirths and miscarriages of male fetuses. More boys than girls die in
infancy. And during each subsequent year of life, mortality rates for males
exceed those for females, so that by age 25 women are in the majority.

For us, these statistics raise two questions: Why do men die so young? And
why do women die so old? From the outset we would like to admit that we 
no definitive answers to these questions. But the available evidence
implicates behavioral as well as biological differences between the sexes,
differences in the effects of medical technology, as well as social and
psychological factors. Ultimately, our investigation of the gender gap in
life span has led us to posit an evolutionary explanation, one that 
that female longevity is more essential, from a Darwinian perspective, than 
the prolonged survival of males. The good news is that in spite of this
evolutionary imperative, the gap between male and female life expectancy 
now be narrowing. The bad news is that some of this convergence may be the
result of women suffering more from what used to be considered "male"

Toxic Testosterone

Comparison of the death rates for men and women in the U.S. at various ages
reveals gender differences in mortality patterns. Although death rates are
higher for males than females at all ages, the difference between the sexes
is more pronounced at certain stages of life. Between 15 and 24 years, for
example, the male-to-female mortality ratio peaks because of a sudden surge
in male deaths with the onset of puberty. During this period, men are three
times more likely to die than women, and most of the male fatalities are
caused by reckless behavior or violence. Motor vehicle accidents are the
most common cause of death for males in this age group, followed by
homicide, suicide, cancer and drowning. Interestingly, a surge in male 
mortality has been observed in other primates at a similar stage in life: 
young adult male macaques, for example, rates of death and "disappearance"
are high compared with those of female macaques.

The difference between male and female mortality declines until late middle
age, when the mortality ratio plateaus. In the 55- to 64-year-old age 
behavior-related fatalities are still among the most common causes of death
for men and are still much higher in men than in women. Men of this age are
more than twice as likely as women to die in car accidents, for example, 
almost four times as likely to take their own lives.

Illnesses related to smoking and alcohol consumption also kill more men 
women in this age group. But heart disease is the main cause of the gender
gap here. Men experience an exponential rise in the risk of heart disease
beginning in their 40s; in contrast, women's risk of dying from heart
disease does not begin to increase until after menopause, and it approaches
the male risk only in extreme old age. Although the gender gap in this age
group is smaller than the one described for young adults, the number of 
people affected by it is far greater. Whereas accidents claim the lives of
45 of every 100,000 young adult males annually, heart disease--the leading
cause of death in men and women alike--kills 500 of every 100,000 men
between the ages of 55 and 64 every year.

Experts suspect that gender differences in mortality patterns may be
influenced at least in part by sex hormones, namely the male hormone
testosterone and the female hormone estrogen. The conspicuous peak in the
sex-mortality ratio at puberty, for example, coincides with increased
testosterone production in men. Because the male hormone has been linked
with aggression and competitiveness as well as libido, some researchers
ascribe this spike in male mortality to "testosterone toxicity." Later in
life, testosterone puts men at risk biologically as well as behaviorally. 
increases blood levels of the bad cholesterol (known as LDL, for low-
lipoprotein) and decreases levels of the good one (HDL, for high-density
lipoprotein), putting men at greater risk of heart disease and stroke.

Estrogen, on the other hand, has beneficial effects on cardiovascular 
health, lowering LDL cholesterol and increasing HDL cholesterol. A recent
study at the University of Washington suggests that estrogen may exert 
effects by regulating the activity of liver enzymes involved in cholesterol

Estrogen is also an antioxidant--that is, it neutralizes certain naturally
occurring, highly reactive chemicals, called oxygen radicals, that have 
implicated in neural and vascular damage and aging. Emerging evidence
suggests that treatment with estrogen after menopause reduces a woman's 
of dying from heart disease and stroke, as well as her risk of dying in
general. Estrogen therapy has also been shown in some studies to delay the
onset of Alzheimer's disease.

It is important to note that with the exception of this evidence regarding
estrogen therapy, the relation between sex hormones and mortality patterns
is still speculative. Furthermore, any attempt to explain mortality 
must include the recognition that these trends are relatively recent. As 
graph shows, the two divergences we have been discussing did not emerge
until the middle of the century. Before that time, the sex-mortality ratio
was constant across age groups for which data are available. The recent
changes can probably be accounted for by two societal factors: improvements
in obstetrical care, which have dramatically reduced women's risks of dying
in childbirth, and an increased availability of guns and cars, which has
contributed to more accidental and violent deaths in young males.

Historical Advantage

Although the reasons women live longer than men may change with time, it
seems likely that women have been outliving men for centuries and perhaps
longer. Even with the sizable risk conferred by childbirth, women lived
longer than men in 1900, and it appears that women have outsurvived men at
least since the 1500s, when the first reliable mortality data were kept.
Sweden was the first country to collect data on death rates nationally; in
that country's earliest records, between 1751 and 1790, the average life
expectancy at birth was 36.6 years for women and 33.7 years for men.

Death rates in less developed countries, whose citizens have limited access
to cars, guns and maternal care, also provide a measure of mortality before
modernity. At present, the only countries in which male life expectancy
exceeds that for females are those with long-standing sexual
discrimination--including Bangladesh, India and Pakistan--where social
pressures and practices such as female infanticide and bride-burning result
in unique "losses" of females.

The fact that women live longer than men does not, however, mean that they
necessarily enjoy better health. It could be that women live with their
diseases, while men die from them. Indeed, there is a difference between 
sexes in disease patterns, with women having more chronic nonfatal
conditions--such as arthritis, osteoporosis and autoimmune disorders--and
men having more fatal conditions, such as heart disease and cancer.

Image: Laurie Grace; Source: Social Security Administration
Differences in the death rates of U.S. men and women have changed over the
past century. Mortality has been consistently higher for men than for women
at all ages (the male-to-female mortality ratio is more than one). In 
recent decades, however, this discrepancy has become even more pronounced 
certain stages of life.

Survival of the Fittest

To understand better the forces that control human aging and longevity, we
have tried to determine whether the longer life span of females might be
part of some grand Darwinian scheme. Gender differences in longevity have
been observed in other members of the animal kingdom: in fact, in almost 
species that have been observed in the wild, females tend to live longer
than males. Female macaques live an average of eight years longer than
males, for example, and female sperm whales outlive their male counterparts
by an average of 30 years.

It seems that a species' life span is roughly correlated with the length of
time that its young remain dependent on adults. We have come to believe 
when a significant, long-term investment of energy is required to ensure 
survival of offspring, evolution favors longevity--in particular, female
longevity. Indeed, we believe that the necessity for female longevity in 
the human reproductive cycle has determined the length of the human life 

We start with the assumption that the longer a woman lives and the more
slowly she ages, the more offspring she can produce and rear to adulthood.
Long-lived women therefore have a selective advantage over women who die
young. Long-lived men would also have an evolutionary advantage over their
shorter-lived peers. But primate studies suggest that men's reproductive
capacity is actually limited more by their access to females than by life
span. Hence, the advantage of longevity for men would not be nearly as
significant as it is for women. And because males historically are not as
involved in child care as females, in the not so distant evolutionary past
the survival of a man's offspring depended not so much on how long he lived
as on how long the children's mother lived.

One might think that the existence of menopause halts the transmission of a
woman's genes and thus contravenes the evolutionary argument for female
longevity. We think just the opposite: menopause confers a selective
advantage and promotes longer life by protecting females from the increased
mortality risk associated with childbirth at advanced age. Even today this
increase in risk is considerable: a woman in her 40s is four to five times
more likely to die in childbirth than a 20-year-old.

When menopause evolved, maternal mortality would have been much greater. If
offspring require a significant maternal investment of time and energy to
survive--which human children most certainly do--then there probably comes 
point in a woman's life when it is more efficient to pass on her genes by
caring for the children and grandchildren she already has than by producing
and nurturing more children, risking death and the death of her existing
children in the bargain. The argument that menopause is an evolutionary
adaptation was first developed in 1957 by George C. Williams, now at the
State University of New York at Stony Brook, and recent anthropological
studies have supported it. Because human children are dependent for such a
long time, continued health and longevity may enhance older women's
contribution to the gene pool even when they can no longer reproduce.

In our own studies of centenarians, we have found that a surprising
proportion of women who lived to be 100 or more gave birth in their 40s. 
of our subjects had even had a child at the age of 53. We found that, 
overall, 100-year-old women were four times as likely to have given birth 
their 40s as a control group of women, born in the same year, who died at
the age of 73. This observation reinforces our suspicion that longevity is
linked with fecundity at an advanced age. Of course, we do not mean that
having a baby in middle age makes a woman live longer. Rather, it seems 
the factors that allow certain older women naturally to conceive and bear
children--a slow rate of aging and perhaps also a decreased susceptibility
to the diseases associated with aging--also improve these women's chances 
living a long time.

We propose that women's longevity edge over men may simply be a by-product
of genetic forces that maximized the length of time during which women 
bear and raise children and perhaps assist with grandchildren as well.
Moreover, male longevity may simply be a function of the fact that men must
carry the genes that ensure longevity to pass them on to their daughters.
Thus, the necessity of female longevity in the human species may be the
force that has determined the natural life span for both men and women. 

The Secret to Living Longer

If female longevity is the product of evolutionary forces, then one might
wonder what physiological mechanisms have evolved to support the
preferential survival of women over men. As we have mentioned, sex hormones
are thought to be important factors in determining the relative
susceptibilities of the genders to aging and disease. Less obvious is the
contribution that menstruation might make to longevity. Because of the
monthly shedding of the uterine lining, premenopausal women typically have
20 percent less blood in their bodies than men and a correspondingly lower
iron load. Because iron ions are essential for the formation of oxygen
radicals, a lower iron load could lead to a lower rate of aging,
cardiovascular disease and other age-related diseases in which oxygen
radicals play a role. Indirect support for this theory comes from studies 
the University of Kuopio in Finland and the University of Minnesota Medical
School. In these studies, male volunteers who made frequent blood donations
had less oxidation of LDL cholesterol--a key step in the development of
atherosclerosis and heart disease.

Women also have a slower metabolism than men--a distinction that makes them
more prone to obesity. But there may also be an inverse relation between
metabolic rate and life span. Evidence of this link comes from animal
studies of food restriction, which slows metabolic processes: in 
sponsored by the National Institute on Aging, monkeys that ate 30 percent
less of the same diet as their free-feeding peers seemed to age more 

Studies of so-called clock genes in microscopic worms have also 
the connection between metabolic rate and life span. Siegfried Hekimi of
McGill University has observed that worms with particular mutations in 
genes live five times as long as normal animals and have much slower
physiological functions. Although it is still not known why men's 
rates are faster than women's, it is becoming clear that this difference is
present almost from the moment of conception, when male embryos divide
faster than female ones. The faster metabolic rate may make men's cells 
vulnerable to breakdown, or it may simply mean that the male life cycle is
completed more promptly than the female one.

Finally, chromosomal differences between men and women may also affect 
their mortality rates. The sex-determining chromosomes can carry genetic 
that cause a number of life-threatening diseases, including muscular
dystrophy and hemophilia. Because women have two X chromosomes, a female
with an abnormal gene on one of her X chromosomes can use the normal gene 
the other and thereby avoid the expression of disease (although she is 
a carrier of the defect). Men, in contrast, have one X chromosome and one Y
chromosome, and so they cannot rely on an alternative chromosome if a gene
on one of the sex chromosomes is defective.

This disadvantage became more ominous when, in 1985, researchers at 
University reported the discovery on the X chromosome of a gene critical to
DNA repair. If a man has a defect in this gene, his body's ability to 
the mutations that arise during cell division could be severely 
The accumulation of such mutations is thought to contribute to aging and

There is also increasing interest in women's second X chromosome as a
longevity factor in and of itself. Although one of the two Xs is randomly 
inactivated early in life, the second X seems to become more active with
increasing age. It may be that genes on the second X "kick in" and
compensate for genes on the first X that have been lost or damaged with 
This compensation could have a sizable influence, as it appears that 
5 percent of the human genome may reside on the X chromosome. In recent
years the X chromosome has also become the focus of the search for genes
that might directly determine human life span.

Closing the Gender Gap

Image: Laurie Grace; Source: Social Security Administration (1990 data)
Women outnumber men by age 25, when they make up 50.3 percent of the U.S.
population; by age 100, women comprise 81.7 percent.

Men and women alike have seen profound gains in life expectancy in this
century. Since 1900, the average national increase in life expectancy in
developed countries has been 71 percent for women and 66 percent for men.
This increase cannot be explained by physiological or evolutionary 
Rather, swift changes in knowledge of health and disease, changes in
lifestyle and behavior, and advances in medical technology have greatly
improved the chances of both sexes' living to old age.

In the past two decades, however, there has been a notable deceleration in
the extension of life expectancy in women. The reasons for this decline are
still being debated. Some researchers feel that women in developed 
are close to reaching the natural limits of human life span, and so their
gains in life expectancy must inevitably diminish.

But some sociologists have discounted this reasoning, pointing instead to
women's changing roles in society. As more women have taken on behaviors 
stresses that were formerly confined to men--smoking, drinking and working
outside the home--they have become more likely to suffer from diseases that
were traditionally considered "masculine." Mortality from lung cancer, for
example, has almost tripled in women in the past two decades. Smoking seems 
to be the "great equalizer" for men and women: current actuarial data from
Bragg Associates in Atlanta show that on average middle-aged female smokers
live no longer than male smokers do.

In part because of these factors, men's and women's death rates in the U.S.
have begun to converge in the past 20 years. But it is primarily the
reduction in male mortality, as opposed to the increase in female 
that is narrowing this gender gap. In general, the higher a nation's level
of social and economic development, the greater the life expectancy for 
men and women and the greater the convergence in the two figures.

Research on sex hormones, sex chromosomes and gender-specific behavior is
sure to further understanding of the human body well beyond the questions
posed by the longevity gender gap. In exploring this intriguing phenomenon,
investigators will undoubtedly find clues to how both men and women can 
longer and more healthy lives.

Related Links

65 + Demographics from Census

Determining Your Longevity

Oldest Old Research

Abstracts on Health and Longevity

Newspaper article on Longevity

The Authors
THOMAS T. PERLS and RUTH C. FRETTS share an interest in the association
between reproductive issues and longevity. Perls is a geriatrician at Beth
Israel Deaconess Medical Center, director of the New England Centenarian
Study and an instructor at Harvard Medical School. Fretts is an
obstetrician-gynecologist at Beth Israel Deaconess Medical Center and an
instructor at Harvard Medical School.



Dr. Linda J. Weyandt MD/ CRNA

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