Scientist: Cell repair key to female longevity

Cells taken from a female body are better at repairing damage compared with cells from a male body. Photo / AP

The reason women live longer than men - and why the final act of sex discrimination favours females over males - may at long last have a scientifically valid explanation.

Scientists believe we are close to understanding why men on average die younger than women.

Past explanations for why women live longer than men, such as men having physically demanding jobs or engaging in riskier activities such as smoking and drinking, cannot fully explain the gender gap.

It has been a major scientific puzzle why members of the "fairer sex", who have in the past been able to retire earlier than men, live longer.

Now the answer to one of the biggest conundrums of human biology may come down to the fact that the female body seems to be better at carrying out the "routine maintenance" that keeps cells alive and ageing at bay - despite the widespread belief in cosmetic circles, based on skin changes alone, that men age more slowly than women.

Professor Tom Kirkwood, a leading gerontologist at the University of Newcastle, believes there is now growing evidence to suggest that men are more disposable than women, because the cells of their bodies are not genetically programmed to last as long as they are in females.

The theory builds on a "eureka moment" that first came to him while having a bath one winter's night in 1977.

Called the "disposable soma" theory, it has become the leading scientific explanation for why we age, why we cannot live forever - and now the reason why women live longer than men.

The theory states that, although the genes are immortal and can indeed "live forever" by being continually passed on to subsequent generations, the body or "soma" is disposable because it is designed to live only long enough to act as a vehicle for carrying genes to the next generation.

The body, just like a car, needs to be maintained continuously to keep it on the road, but as time progresses, the faults and errors build up within the cells and tissues. These faults are energetically expensive to fix and with time, they become so common that the body eventually succumbs and dies. When this occurs depends on how much effort the body spends on fixing its mistakes.

"Could it be that women live longer because they are less disposable than men? This notion, in fact, makes excellent biological sense," Professor Kirkwood suggests in an article to be published in the November issue of the magazine Scientific American.

"In humans, as in most animal species, the state of the female body is very important for the success of reproduction.

"So if the female animal's body is too much weakened by damage, there is a real threat to her chances of making healthy offspring. The man's reproductive role, on the other hand, is less directly dependent on his continued good health," Professor Kirkwood writes.

There is growing evidence to back up the idea. Females of most species tend to live longer than males, and experiments in Professor Kirkwood's own laboratory have shown that animals that are naturally long-lived have better maintenance and repair systems than shorter-lived species.

Studies have also found that cells taken from a female body are better at repairing damage compared with cells from a male body. Interestingly, this difference between the sexes is eliminated if the female cells come from a body where the ovaries have been surgically removed.

Equally, being a fully functional male seems to be bad for longevity compared with a male that has had his testes removed. Neutered male cats and dogs, for instance, often live longer than normal males, and even in humans there is evidence that castrated men live longer than other men, Professor Kirkwood said.

Bodies of evidence

* The gender differences become more apparent with age.

* There are roughly six women to every four men by the age of 85, and the ratio is more than two to one at the age of 100.

* The oldest documented person to have ever lived was Jeanne Calment, a French woman who died in 1997 at the age of 122 years and 164 days.

- INDEPENDENT