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THE key to women鈥檚 longevity may lie with their stronger immune systems.
Traditionally, men鈥檚 shorter lives have been put down to the greater risks they
take, but researchers have come up with a tantalising new theory after finding
that women produce more new immune cells than men.

It鈥檚 the thymus gland that鈥檚 responsible for churning out the T cells that
fight off infections, but it wastes away with age. To find out what effect this
deterioration has on the production of T cells, Richard Aspinall, Jeffery
Pido-Lopez and their team at the Imperial College School of Medicine in London
tracked the number of new T cells produced in 46 healthy men and women between
the ages of 20 and 62. While the thymus made fewer new cells with age in both
sexes, women still had higher levels of new T cells than men of the same
age.

To check if this advantage did give women more protection against infections,
the researchers looked at deaths in Britain from pneumonia and influenza between
1993 and 1998. They found that more men than women died of these diseases, and
the trend mirrored the difference in thymus activity between the sexes. 鈥淭here
are a host of factors that could contribute to susceptibility to infection, of
which thymic output might be one,鈥� says Aspinall.

鈥淒uring old age, when old T cells are not as effective, a higher replacement
of old T cells with new ones would be a bonus,鈥� says Pido-Lopez. But that
doesn鈥檛 exclude the risk theory altogether. 鈥淩isk can explain anything from
number of car crash deaths to deaths from colon cancer,鈥� says Aspinall. 鈥淏ut
there are probably other factors [such as thymic output] that contribute to the
difference in longevity.鈥�