Dec. 23, 1999 (Atlanta) -- Having babies takes years off mothers' lives -- if the mothers are fruit flies. A new study shows that the ability of fruit flies to lay eggs at an early age is directly linked to aging and early death. The extent to which these findings can be extended to humans, however, is by no means clear.
"It is the direct impact of the early reproductive effort that causes this wave of death," co-researcher Linda Partridge, PhD, tells WebMD. "Processes having to do with reproduction -- processes that we would not recognize immediately as reproduction itself -- may be in some way responsible for the damage that causes aging."
Partridge and her colleague Carla M. Sgrò, PhD, set up an elegant series of experiments to find out why greater reproductive activity reduces life span in many animal species. The results of the study are published in the current issue of the journal Science.
The researchers first showed that fruit flies die sooner if they are genetically predisposed to lay eggs earlier rather than later in life. This "wave of death," as the investigators refer to it, sweeps over the so-called young breeders when they reach middle age; individuals who survive go on to live as long as the old breeders. Infertile young breeders, the researchers found, have normal life spans.
"The implication of the finding is that if you block the early [breeding or multiplying], you also stop them having that wave of death when they are old," Partridge says.
Huber Warner, PhD, deputy associate director of the biology of aging program at the National Institute on Aging (NIA), tells WebMD that there is a sort of "trade-off" between reproduction and aging.
"There's a hell of a cost for a woman to conceive and have a child in terms of just biological wear and tear," Warner says. "Let's just assume that in life you have a certain amount of energy to burn. If you burn it up having children there's less left to maintain the homeostasis [stable equilibrium] of the individual."
But this does not mean that the fruit fly findings apply directly to women. Rose Li, PhD, NIA chief of demography and population epidemiology, tells WebMD that the fruit fly findings are interesting, but that they do not mean that women who have babies early in life are going to die sooner than those who do not.
Arun K. Roy, PhD, is more emphatic. "In the human population, there is no correlation between the number of children a woman bears and life expectancy," he tells WebMD in an interview seeking objective comment. "In fact, there is an opposite correlation."
Roy, a professor in the department of cell biology at the University of Texas Health Science Center in San Antonio, takes issue with the suggestion by Sgrò and Partridge that aging has evolved primarily because of the damaging effects of reproduction earlier in life.
"I think [the Sgrò and Partridge study] is very interesting, but it is difficult to generalize the profound implications of reproduction for aging from studies of fruit flies," he says. "In the case of fruit flies, a large chunk of the body mass is used for reproduction. Reproduction does have a tremendous deleterious effect. But that's not true for higher animals. That makes a big, big, difference."
- Researchers have found that fruit flies that lay eggs early in their lives tend to die younger than fruit flies that lay eggs laVital Information:ter.
- In humans, there is no evidence that giving birth at a young age affects life span