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London: Giving birth to sons is more stressful for mothers and can even shorten their livespans, a new Finnish study has claimed.
Researchers studied demographic data from pre-industrial Finland to show that irrespective of access to resources, mothers but not fathers with many sons suffered from reduced survival.
However, this association reduced as mothers got older.
Information on a total of 11,166 women and 6,360 men born between the seventeenth and twentieth centuries was studied.
The more sons a woman had, the more likely she was to live a shorter time after last giving birth. The study found that the effect held whether women were rich or poor, The Telegraph reported.
"Our results provide evidence that Finnish mothers traded long post-reproductive lifespan for giving birth to many sons," Dr Samuli Helle, of the University of Turku, said.
Previous research has suggested that bearing sons is especially costly for the mother because they are, on average, born heavier and place more physical stresses on the body.
Having sons can also raise levels of testosterone in their mothers, which can age the immune system, making it less able to defend the body.
"Women's post reproductive survival declined with the number of sons they gave birth to. This association did not depend on their socio-economic status but was age dependent.
That is, the survival costs of the number of sons born decreased linearly as women aged," Helle said.
The number of daughters born was not connected to women's lifespan and, in men, neither the number of sons nor daughters born were related to their survival, irrespective of their socioeconomic status, according to the study.
"Our results show producing sons shortened the post reproductive lifespan of Finnish women and this association detoriated as mothers aged. This supports our hypothesis that production of sons is more energetically costly than the production of daughters," Helle was quoted as saying by the paper.
"The reduction of reproductive costs with age may be due to the potential beneficial social influences of surviving sons, as the number of adult sons was unrelated to post-reproductive lifespan in these women," Helle said.
