Sons may shorten life span of mothers, researchers say

WASHINGTON --"My son will be the death of me yet."

The familiar lament by mothers everywhere may have a kernel of scientific truth, researchers say.

A study analyzing church records in earlier centuries found that having sons shortened the life span of Finnish mothers by about 34 weeks per son. Daughters nurtured to adulthood helped prolong mothers' lives.

Baby sons, researchers suggest in the journal Science, make a much greater physical demand on the mother's body than do the typically smaller daughters and this may actually lead to a shorter life for the mother.

"Boys are usually born much heavier than girls," said Samuli Helle, a researcher at the University of Turku in Finland and the study co-author. "It seems that boys are much more demanding to produce than girls."

Finnish records

Helle said the conclusion is based on church family records kept in Finland for a nomadic people called the Sami during the period 1640 to 1870. He said the toll on mothers lives of having sons may not apply in the era of modern medicine.

"Nowadays we have better medical care," Helle said. "Resources are not as likely to limit females' life span. There might be some effect, but it will not be as huge as in the Sami people."

Helle and his co-authors used the records because of their accuracy and because they gave a measure of the effects of natural mortality before advance medical care.

The study concentrated on women who produced children and then went on to live past age 50. The researchers found that women who gave birth to sons had a shorter life span than those who had only daughters. Typically, a mother's life was shortened by about 34 weeks per son.

Having daughters who were raised to adulthood diminished the effect, actually helping the mothers live longer, Helle said.

"You can actually cancel the negative effect of one boy by producing about three girls," said Helle. "The girls stayed in their natal group for quite a long time. All the children had a great influence on their parents' lives, but the girls had a more positive effect than the boys."

During the study period, Sami families typically had four children per generation. The children tended to stay with the family, creating an extended family group that spanned several generations.