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Wednesday, 29 March, 2000, 18:19 GMT 19:19 UK
Women grow old genetically

Women may be genetically suited to long life
Women have a natural genetic advantage over men which allows them to live longer, scientists have shown.

Despite the less healthy lifestyles of men in the past compared to women, experts have still been slightly puzzled as to why the average lifespan of a woman approaches 80 years, while the average man lives some four or five years less.

However, a team of scientists from Denmark and Norway claim to have found a reason why women last longer.

The secret, they say, lies in the chromosomes in each cell, which hold all the genetic instructions to make the body function properly.

A man will have one "X" sex chromosome, handed down from his mother, and one "Y" sex chromosome from the father.

Because of this, men have only one copy of some key genes which are found on the maternal, or "X" chromosome.

However, in women, there are two "X" chromosomes, meaning that the woman essentially has two different sources for some key genes.

In effect, women have two "cell lines", or chromosomes. Each individual cell uses one of these when it is created.

Older women

However, when cells from older women - aged between 73 and 93 - were examined, they appeared to be using one particular cell line more frequently.

And when ageing identical twins were checked, they were in many cases both using one particular cell line more frequently.

Kaare Christensen, of Odense University in Denmark, said: "This suggests that one 'cell line' is better than the other.

"Males have only one cell line. So they have only one chance."

Studies in animals back up this theory. In mammals, males generally have the two different sex chromosomes - and they have shorter lifespans than females, who have two.

In birds, the reverse is true - and male birds generally outlive the females.

Although many scientists believe there is a genetic reason why women live longer than men, conventional wisdom states that there are other significant reasons why this should be the case.

In particular, men have historically smoked more and drunk more alcohol than women.

Women are also less likely to die early from heart disease, as the female sex hormone oestrogen has a protective effect.

This effect is lost quickly after the menopause, when female heart disease mortality quickly matches that of men.

A spokesman for the British Heart Foundation said: "In part, genetics must have a role, and scientists don't yet know exactly why women live longer.

"But women's health behaviours have been traditionally better than those of men."

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02 Feb 99 | Health
Exercise 'can reverse ageing'
12 Jan 99 | Health
Smoking hits women hard
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