The Feminine Advantage

Women on average live longer than men. As biologists wrestle with the mechanism, sociologists grapple with the repercussions: The extra years can leave women in financial ruins when they are most vulnerable.

Men have all sorts of advantages over women: They make more money, they look distinguished with gray hair, and they get better deals on used cars. But their good luck runs out near the end of life, when women outlive them by almost a decade.

Experts aren't sure why women generally live longer than men, but "if we [could] understand the mechanism, we could advise everyone how to do it," says physiologist José Viña of the Universidad de Valencia, Spain. Unfortunately, living longer isn't necessarily a good thing, say researchers who study older women navigating the far reaches of their lives: Very old women are often poorer and more likely to be alone than men are. What's more, social and health care policies don't adequately address their plight.

According to experts, women's longevity edge is likely to be part environmental--men on average live riskier lives, for example--and part biological. "We see gender differences in life expectancy across species--and it's the females that consistently live longer," says biodemographer S. Jay Olshansky of the University of Illinois, Chicago.

In seeking biological explanations, some researchers start with estrogen, a hormone that premenopausal women, but not men, manufacture in large quantities. Previous work has shown that estrogen can crank up genes that encode antioxidants, compounds that clean up destructive molecules made in cells as a byproduct of metabolism. One theory of aging says that accumulated oxidative damage could contribute to aging through wear and tear on cells and tissues (see "Villain or Victim?").  Viña has found that removing the ovaries, which make estrogen, from female rats quadruples the amount of injury within the animals' cells. He postulates that the protective effect of estrogen could give women an advantage over men.

Estrogen also stimulates production of a protein called telomerase, which can replenish chromosome ends called telomeres. Each time most types of cells divide, these telomeres diminish. In principle, telomerase could replace the dwindling ends--but many human tissues turn the enzyme off. The progenitors of some rapidly dividing cells such as skin and white blood cells, however, continue to produce a smidgen. Some studies in humans suggest that people with stubbier telomeres die from cardiovascular diseases earlier than do folks with more ample caps (see "Telomere Tales").  Telomeres in women's white blood cells, which are known to be able to respond to estrogen, tend to be longer than those in men's are, perhaps because of estrogen. This difference might help account for the female longevity advantage, says cardiovascular physiologist Abraham Aviv of the University of Medicine and Dentistry of New Jersey, Newark.

But estrogen itself is not a practical solution. "We can't give estrogen to men or to women because of the possibility of breast and uterine cancer," Viña says. Instead, he and his colleagues will be testing phytoestrogens, estrogenlike compounds that also stimulate the antioxidant genes, for their ability to increase rat life span. Although these compounds have not been widely tested for their relative safety, they are widely consumed in products that contain soy.

Another major biological difference between males and females lies in the X chromosome. Women have two copies of the X chromosome, whereas men have only one. To accommodate this chromosomal imbalance, each cell in a female shuts down most of the genes on one X chromosome to prevent double the amount of proteins being made. At birth, about half of the cells in an individual use the X that came from mom and about half use dad's.

By the end of life, however, that 50:50 split can become skewed--particularly in women over 65, finds geneticist Carmen Sapienza of Temple University School of Medicine in Philadelphia, Pennsylvania. Sapienza tracked X inactivation in individual women over time and found that whereas a 70-year-old might be using her dad's X in 60% of her cells, 20 years later, that value might be 80%.

The X distribution grows increasingly lopsided in older women, Sapienza posits, because one of the chromosomes might possess a set of genes that endows the cell that uses it with a survival advantage. And as the ability to regenerate tissues decreases with age, cells that happen to be using the more fit X chromosome are more likely to survive and repopulate dilapidated tissues than are those that shut it down, thereby tilting the X ratio more.

The additional unevenness might also buttress telomeres, says Aviv. He and his colleagues found evidence last year of a gene (or genes) that resides on the X chromosome and influences telomere length. So, if a woman inherits an X chromosome that bears a gene for long telomeres--and she activates that chromosome preferentially in the majority of her cells--perhaps she'll enjoy healthier tissues and a longer life.

Sadly, longevity has its downside. Additional time "means that older women are more likely to be living alone and be living in poverty," says gerontologist Nancy Hooyman of the University of Washington School of Social Work in Seattle. Thirteen percent of elderly women in America are poor--twice as many as elderly men. Throw in the race card, and the number skyrockets: 60% of older Latina women and 75% of older African-American women are poor.

The condition arises from a lifetime of inequity between the sexes, says Hooyman: Women earn 71 cents to the dollar that men make. In addition, many take time off from work outside the home to raise children, and in some cases, grandchildren, further reducing their incomes and Social Security benefits. And the ailments of aging make matters worse. Although couples might think they have plenty of money for retirement, they often spend joint resources caring for husbands through terminal illnesses. Because men tend to die first, wives bear the brunt of these financial shortfalls. "Just about the time she realizes what kind of shape she is in financially, the woman will have her own health-care crisis," says lawyer and physician Patricia Kuszler, also at the University of Washington.

But amid the potential hardships, a plus side does exist, Hooyman says: "Women are more likely than men to have strong social networks that they can draw upon." And friends and family can help women navigate the medical and financial challenges that accompany old age--or at the very least, give them someone with whom to commiserate.

Mary Beckman is a writer in southeastern Idaho who really needs to start saving for retirement

Older Women's League: http://www.owl-national.org/

Note: This article addresses issues that will be discussed during a special debate on "Women and Aging" cosponsored by the Women's Bioethics Project and SAGE Crossroads. The live event will take place in Seattle, Washington, on June 8, and the discussion will be rebroadcast in a webcast on June 21.