BBC Science Correspondent Sue Nelson: Uncovering secrets of long life

The association has already been shown in flies and now a study of the British aristocracy appears to indicate the same is true in humans.

Professor Thomas Kirkwood, from the University of Manchester, and Rudi Westendorp, of Leiden University in Holland, scoured the records of 19,830 male and 13,667 female aristocrats born between the year 740 and 1875.

From these records they could see that the women who had their first child at an early age died younger than those who had their firstborn later in life. When only post-menopausal women were considered (aged 60 and over), those who had had the fewest children, and waited longer to have their first child, lived the longest.

Almost half the women who lived beyond the age of 81 had no children, yet fewer than a third of the women who died before that age were childless.

Computerised records

British aristocratic families turn out to provide an ideal database for testing the theory. Their lifestyles are fairly similar and this reduces the chances of any analysis being skewed by factors such as poverty.

Professor Kirkwood: The study helps us understand the ageing process

"Extensive genealogical records have been kept for aristocratic families dating back to as early as the year 740," the authors write in Nature. "These records have been published and computerised."

They include ancestors of the present Queen, the Prince of Wales, and a host of hereditary peers ranging from the Dukes and Earls of Abercorn to the Barons of Willoughby de Broke.

The research mirrors the findings of experiments done on the fruit fly, Drosophila melanogaster. Flies that were prevented from mating, or which bred later in life, lived longer.

The authors write: "The data for humans presented here, and the increased likelihood that a woman becomes a centenarian when she bears children at a later age (in her 40s) are reminiscent of the Drosophila experiments and support the predictions of evolutionary theories of ageing,"

Cell repair

The explanation for the link between longevity and late reproduction may lie in an idea first proposed by Professor Kirkwood 20 years ago.

He put forward the "disposable soma" theory which predicted that any investment in reproduction diverts resources away from the maintenance and repair of cells. Ageing is the consequence.

"Its not so much that an individual can chose not to have children and live longer," says Professor Kirkwood. "There is, however, a pattern, and what we see in populations is that those that have the potential to live the longest life tend to have lower fertility than the average."

"What the data suggest is that if you have your first child later, perhaps because your fertility is a little bit lower than the average and you have difficulty getting pregnant, then it may be this is because your body is putting more of its effort into things that will keep you going and relatively less into the things that aid fertility."

Queen Victoria

Daniel Promislow, from the University of Georgia, in Athens, USA, writes a commentary to accompany the Nature paper. He says the results are "powerful evidence for a correlation between reproduction and longevity in British aristocrats".

But he warns the results "do not prove causation". He says many factors influence lifespan and having more children does not necessarily doom a person to an early grave.

"After all, Queen Victoria gave birth to nine offspring, all of whom survived, and lived to be 81-years-old - in her day, a ripe old age."

Professor Kirkwood also stresses that the research has little day-to-day relevance for those thinking about having children. But he believes the study will help us understand better the process of ageing.