Having Sons Shortens a Woman's Lifespan, But Having Daughters Lengthens It
Having sons can shorten a woman's lifespan, according to a new study that found that mothers who give birth to sons live slightly shorter lives than mothers who give birth to daughters.
The latest study on Finnish villagers in pre-Industrial Scandinavia, found that women who had sons lived for an average of eight and a half months less after completing their family than women who only had daughters.
The findings, published in the Royal Society journal Biology Letters, revealed that a woman's risk of death increases by 7 percent per year for each son born.
Furthermore the shorter life expectancy of women who have sons was independent of wealth or social status of the mothers, according to researchers. However, the study found that the gender of the children made no difference to the father's life expectancy, leading researchers to suggest that there may be a biological reason why women who have only boys die younger.
Lead researcher Dr. Samuli Helle of the University of Turku in Finland and his team examined parish records kept by the Lutheran Church.
They looked specifically at post-reproductive survival of more than 11,000 mothers from the 17th to 20th centuries living in a mostly agricultural society with no access to modern birth control or medical care.
After analyzing the data, researcher found that if a woman living in these communities was 37 years old at the time of giving birth to her last child, then her life expectancy would vary depending on the sex of her children. She would live for another 33.1 years after her final labor if she had no sons, another 32.7 years if she had three sons and 32.4 years if she had six sons.
The latest research is supports previous research published 2002 in the journal Science that revealed that for every son a woman had, her life would be shortened by an average of 34 weeks. In contrast, the study had found that daughters actually slightly lengthened their mother's lifespan.
Researcher speculated that the difference in lifespan could be because woman who give birth to boys have more testosterone, a hormone known to weaken the immune system. Another reason could be that boys grow faster in the womb and are usually heavier to carry, which places more strain on the mother's body. Previous studies have also suggested that women expend more energy in producing breast milk for boys, according to Nature.
Helle and his team added that social and cultural reasons could also play a role in determining a mother's life expectancy, like additional support given to mothers by their daughters may help lengthen lifespan.
"The relative importance of biological versus cultural factors remains an open question," Helle told Nature. "We need more data, such as how many sons versus daughters helped in everyday tasks, what age they actually started to work outside the home and so on."