Centenarians - More Gender Differences

Robert W. Griffith, MD
August 20, 2004

Professor Thomas Perls of Harvard Medical School is the founder of the New England Centenarian Study (NECS); this study reports on the heath of some of the United States' oldest citizens. He has distilled the most interesting results in his book "Living to 100". Here is the 5 ^th in our series of extracts from the book. Robert Griffith, Editor.

We were getting used to the fact that so many of our assumptions about aging were turning out to be false. Most of the important issues of male-female differences were already decided by myth and stereotype.

Maintenance of Personal Connections and Relationships

Contemporary health research has recognized that isolation from friends can be detrimental to your health through the life cycle and in old age may even be lethal. As their siblings and contemporaries begin to die, both men and women depend heavily on friends and younger relatives. Curiously, however, we noted that a healthy wife could pull her husband along for a lap or a lap-and-a-half. And once her spouse died, she was usually able to continue the race independently.

Men, however, seemed even more dependent on relationships than women. Any man who wants to live to 100 must be behaviorally suited to getting over the possible losses that women seem to survive more easily. If a man's wife lives along with him to extreme old age, that would probably improve his chances significantly. Although we had met several lifelong single female centenarians, all of the men in our study had been married at some point in life, and many of our oldest men had enjoyed 70-and 80-year marriages. This stable companionship probably helped these men aged much more successfully. But the loss of a wife is usually too high a hurdle for men to clear.

The Role of Sex Hormones?

We saw that only the most clear-cut, obvious differences between the sexes would help us come to any reliable conclusions about female longevity. First we had to consider the effects of sex hormones. Men make significantly more testosterone than women, and women make more estrogen than men, at least until menopause. These hormones are responsible for a significant portion of the differences between male and female physiology, and temperament as well. They also appear to have a dramatic effect on how people perform in the longevity marathon. However, the relationship between sex hormones and mortality patterns is still speculative.

Iron Metabolism

We and a few other scientists are evaluating the potentially significant effects of menstruation, which may impact longevity in ways never before considered. With the monthly shedding of the uterine lining, premenopausal women typically have a significantly lower iron load in their bodies than men. Since iron ions are essential for the formation of free radicals, a lower iron burden could lead to a slower rate of aging, reduced cardiovascular disease, and decreased susceptibility to other age-related diseases in which free radicals play a role.

Iron is a vital nutrient required by red blood cells to transport oxygen throughout the body. Physicians have traditionally prescribed iron replacement for premenopausal women with "iron-poor blood." It's possible that higher iron levels, which may have been consider "normal" only because they are common in males, actually speed the aging process. In studies at the University of Kuopio in Finland and the University of Minnesota Medical School in Minneapolis, male volunteers who made frequent blood donations showed heightened resistance to the oxidation of LDL cholesterol - a key step in the development of atherosclerosis and heart disease. The blood loss of menstruation could be as important in combating oxidation as estrogen is, if not more so.

If our efforts in those of the Nurses Health Study -- which is now considering the link between iron levels and oxidative damage -- bear out our theories, it could have important implications for iron replacement therapy, and treatment of diseases of aging. Although dietary iron is of great importance in children to ensure adequate red blood cell production, it may turn out that adults, and perhaps even adolescents, are speedy up their aging clocks by maintaining iron levels that are now considered "normal," but may in fact be excessive. Iron supplementation for premenopausal women may go the way of general anesthesia during childbirth. Regular blood donation, which lowers iron, may turn out to be more than an altruistic act; for men and postmenopausal women, it may actually improve chances of longevity by reducing the rate of oxidative damage. [However, please see the first link below, posted on our Public pages. Robert Griffith, Editor]

And Later Childbirth?

The link between menstruation, reproductive ability, and healthy aging became even stronger when an unexpected finding cropped up in our study. As we began checking the birth dates of more centenarians' children, we saw a new pattern emerging: about 20% of centenarian women had borne children past the age of 40. Using death certificates from the Massachusetts Office of Vital Records and obituaries from the Boston Globe, we identified 54 women who were born in 1896 and died in 1969, and compared them with 78 women in our study who had turned 100 in 1996. Both groups had contended with the same social and environmental conditions, and had been supported by the same healthcare system throughout their lives. The only major differences between the two groups was that one group of women had died at 73, which was the average life expectancy for women at the time, while the other was still living at 100.

We felt sure that centenarian women were more capable of having children in their forties than shorter lived women. But would the study bear out our suspicions? The results that came back were persuasive: only 6% of the women who had died at age 73 had borne children past their 40th birthdays. Twenty percent of the centenarian women had borne children beyond the age of 40, and they were four times more likely to have borne children in their forties than women who had lived to age 73.

"Should women try to have children later in life?" we were asked. The answer is no; having children is normally much safer and healthier for mother and baby during the conventional childbearing years. It's having the potential to bear a child later that's associated with longevity - not actually having the child. A healthy reproductive system after 40 is a marker of extremely slow aging.

Is Evolution Behind it All?

Longer life spans afford women an opportunity to bear more children, as well as to assure their survival. The need to ensure the survival of more children to reproductive age led to the selection of genes that extended female lifespan. Longevity-enabling genes are inherited by men as well as women, but it is women who are evolutionarily responsible for the lifespan of the human species.

At first glance, it would seem to follow that longer-lived men would also have an evolutionary advantage in passing on their genes. But primate studies suggest the males' reproductive capacity is determined less by their length of life than by access to females. So the survival of a man's children depends not so much on how long he lives as how long the children's mother lives. Males, it appears, are simply "carriers" of longevity-enabling genes; they may or may not achieve longevity themselves, based on their behavior and life circumstances. But the reason they've inherited the capability is primarily to pass it along to their daughters.

In the next extracts from his book, Professor Perls describes how his team looked further into the role of genetics in longevity, and made a surprising discovery. You can buy his book "Living to 100" at Amazon; click here

Source

• Living to 100: Lessons in Living To Your Maximum Potential at Any Age. TT. Perls, MH. Silver, 1st edition, Basic Books, New York, NY, 1999

Related Links
Lack of Iron Lowers Immunity
The Centenarians Study
The New England Centenarian Study
The World Takes a New Look at Aging

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