If you know somebody who has had a child after her 40th birthday, you may have met a future centenarian. Scientists have discovered that bearing a baby in the fifth decade of life is a strong indicator that a woman has anti-ageing genes which will help her reach the age of 100.
The result could lead towards the identification of the estimated 8,000- odd genes which slow down the natural process of ageing. It also provides support for research suggesting that hormone replacement therapy after the menopause will also help extend a woman's life.
According to an American study comparing a group of women born in 1896 who reached 100 with others born in the same year who died aged 73, the centenarians were much more likely to have had a child in their forties than those who died at a "normal" age.
However, women seeking to live longer should not rush into their lover's arms (or the sperm bank). It is not the act of having a child after 40 which leads to a congratulatory royal telegram 60 years later. The key factor is the genes that the child's mother was born with. Having the baby does not confer the genes.
For the women born in 1896, successfully bearing a child during a 10- year period which included the Second World War indicated that nature had endowed them with the ideal genetic makeup for a long life.
Thomas Perls, who carried out the research at the gerontology division of the Harvard Medical School, said yesterday: "It helps the result that none of them would have had artificial oestrogen therapy, so we know what we're seeing was genetic."
The research, published today in the science journal Nature, adds to the confusing scientific literature which women can weigh up when trying to decide at what age - if at all - to have children.
Previously, research has demonstrated that the younger a woman is when she has her first child, the less likely she is to develop breast cancer during her life. The effect may be due to the growth of the breasts during pregnancy.
Plentiful evidence also shows that the older the mother, the more likely it is the embryo will suffer from a genetic defect such as Down's syndrome. That is thought to be because the eggs accumulate genetic damage.
Because the longer-lived women went through menopause later, the result suggests that the oestrogen their bodies produced also helped them survive longer, avoiding age-related diseases like Alzheimer's.
Dr Perls is now following up the work by studying the children of the women from the research group, and also looking for families where there are two or more siblings aged over 90.
By comparing blood samples, he hopes to find long stretches of DNA which represent "the city in which the anti-aging genes have their home". After that, he hopes to find the genes responsible - though it may be the work of a lifetime.
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