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Thursday, 9 May, 2002, 18:01 GMT 19:01 UK
Boys 'shorten mums' lives'
Daughters may have been more help to mothers
Daughters may have been more help to mothers
Having sons cut mothers' lives short, according to researchers looking at families 200 years ago.

The pattern might still be seen in developing countries today, but women in modern industrialised societies would be less affected, they suggested.

The team from the UK and Finland looked at church records for the Sami people of Finland ('Lapps'), from the 17th and 19th Centuries.

The Sami depended on reindeer herding, fishing and hunting for their livelihood and lacked advanced medical care.

Perhaps girls are more likely to help with gathering food and caring for children

Samuli Helle, University of Turku, Finland
The researchers found that, compared with daughters, having sons significantly shortened the lifespan of mothers.

On average, the reduction was 34 weeks per son, though it ranged from four to 64.

Daughters increased a mother's life expectancy by an average of 23 weeks.

Mothers with many daughters who survived to adulthood had the longest lifespans in these pre-industrial Sami people.

A woman's longevity was not related to her total family size.

Long-term cost

Boys took more of a toll on mothers than girls because they grew faster in the womb, were heavier at birth and required more care after birth, the researchers added.

They suggested men's lifespans were not affected by the number or gender of their children because they did not suffer direct physiological costs of reproduction as women do.

In the journal Science, the researchers wrote: "Our results suggest that giving birth to sons had a higher relative long-term survival cost for mothers than giving birth to and raising daughters.

Samuli Helle of the University of Turku, Finland, who led the research, told BBC News Online there was no definite explanation for the lifespan difference, but suggested: "Perhaps girls are more likely to help with gathering food and caring for children."

Dr Virpi Lummaa, of Cambridge University's Department of Zoology, who also worked on the study, said: "The basic findings that sons and daughters can be differently costly for the mothers' health probably still applies, but the consequences of this for mothers' health might be less dramatic than it was in those days.

"Modern women, who are having fewer children, live in plentiful conditions. They can probably afford to have many sons and still live longer."

Population patterns

She told BBC News Online it was possible that the same pattern was seen in developing countries today.

"Where mothers are having many children, no medical care, have high mortality rates - these kinds of things could still appear there."

Dr Daryl Shanley, of the Department of Gerontology at the University of Newcastle, said: "Without further information on the mechanisms that underlay these results, extension to human populations with access to modern medical care is not clear."

He said the data in the Finnish study was from a time when family sizes and child mortality were high.

"Reproductive costs in populations that have undergone the demographic transition [from high to low birth and death rates] are not likely to be as sensitive to the gender of the child."

See also:

26 Apr 02 | Health
Mystery of baby gender patterns
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