Women who have children young may have triggered their own genetic time bomb, according to new research.

Scientists compared the fate of female fruit flies bred to reproduce at different ages.

Later reproducing flies generally had a longer life span.

Cost of reproduction

Researchers have long known that there is a price to pay for reproduction, which increases the death rate in many species.

But the new study suggests the cost is incurred after a delay. The genetic changes triggered by reproduction appear not to take effect until later in life, at the onset of ageing.

The research conducted by Carlo Sgro and Linda Partridge at University College, London is reported in detail by the journal Science.

The researchers say further investigation is needed.

Genetic damage

"Reproduction" they write, "may cause damage directly, and the effects may accumulate with time. Reproduction may also divert nutrients from repair and defence, resulting in more rapid accumulation of damage."

The deceleration of death rate at later ages was possibly the result of repairs being made to genetic damage occurring earlier.

Once the reproductive phase of life was over, more nutrient resources could be diverted to carry out repairs.