Friday, September 7, 2007

Sons do not shorten maternal life

New research has refuted what Science magazine reported five years ago and what has been cited time and again, and not always properly. Good news for all mothers: There is not the least evidence that giving birth to a son as compared to a daughter ever has shortened or ever will shorten the life of a woman.

Back in May 2002, Helle and co-workers have analyzed population register data of pre-industrial Sweden and found that giving birth to sons shortened the life of women. They were even ready to explain this correlation: Sons, in their opinion, are a greater physiologic burden than daughters, and the testosterone produced by the male fetuses may have a negative impact on the hormone balance of the women.

Despite the fact that this analysis has been restricted to a pre-industrial population, the finding has been spread by popular media as relevant for women of today: "Those sons really will be the death of you, mom" has shown up at position 20 of a Google search today.

More data unmask a bias

Recently, Cesarini and co-workers have re-analyzed the Swedish data and published their new findings on maternal longevity and the sex of offspring in pre-industrial Sweden. Extending the original database of Helle and others by considerably more data from the same region and time period, they no longer found any evidence of a negative impact of sons. It seems that the smaller database of Helle has been affected by some variable bias that has not been filtered out properly.

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