Boys can be a handful for both parents, but they only seem to take a toll on their mothers' life expectancy.
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From Nature magazine.
Women who bear sons can have slightly shorter lives than those who bear daughters, researchers have found. Their study showed that a woman’s risk of death increased by 7% per year for each son born — a small but statistically robust effect, at least for the individuals the team looked at — Finnish villagers in pre-Industrial Scandinavia.
“Previous investigations into the effect of the gender of a baby on its mother’s lifespan have been mixed, so our new analysis really is just another brick in the wall,” says Samuli Helle of the University of Turku in Finland, the study's lead author. “I’m not surprised the results have been mixed, because the previous studies have involved different societies, cultural practices and so on.”
A litany of factors could influence a woman’s lifespan, such as affluence and nutrition, as well as the number of children she has. The impact of having a boy compared with a girl is likely to be most pronounced in settings where resources such as food and health care are poor.
Helle and his co-author, Virpi Lummaafound, investigated parish records for individuals in eight parishes who lived during the seventeenth to mid-twentieth centuries. They found that if a woman in these communities was 37 years old at the time of having her last child, her life expectancy would vary depending on the sex of her children. She would live for another 33.1 years if she had no sons, another 32.7 years if she had three and another 32.4 years if she had six.
The study, which appears in Biology Letters, builds on previous research published by the same team in the journal Science more than ten years ago, which found that for every son she had, a woman's life would be shortened by an average of 34 weeks. By contrast, daughters actually lengthened their mother's lifespan very slightly (though not statistically significantly). In both studies, the life-shortening effects were experienced only by mothers, not fathers.
Biological factors
But the reason behind this small difference is the big puzzle. “The relative importance of biological versus cultural factors remains an open question,” says Helle, who speculates that it could be that girls are more likely to help their parents in household duties. “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.”
Erik Lindqvist of the Research Institute of Industrial Economics in Stockholm, who has looked at lifespan and births in Sweden, is not convinced. “We have never been able to replicate their results," he says.
But Grazyna Jasienska, who studies longevity and reproductive health at Jagiellonian University Medical College in Cracow, Poland, believes that the effects of sons on a woman's lifespan are certainly real — and are probably due to biological factors, such as breastfeeding.
Other studies have found that boys can take more of a toll on their mother biologically because they tend to be slightly heavier at birth than girls. And a few studies have found that women expend more energy in producing breast milk for boys — although the results of such studies have been mixed.
“I think the costs of having boys over girls are more social than biological," she says. "But we still ultimately don’t know."
This story is reprinted with permission from Nature magazine. It was first published on February 27, 2013.
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22 Comments
Add CommentIs there meaning to the phrase 'shorten life expectancy'? Wouldn't 'shorten life' cover it in any case? I'm not sure if a statistical prediction can be 'shortened'. Possibly, 'reduce life expectancy' or 'reduce life expectancy value'.
Reply | Report Abuse | Link to thisAs a parent, there's no doubt female children shorten the lives of BOTH parents.
Reply | Report Abuse | Link to thisWhat evidence is there that this is causation rather than correlation with other factors being the cause?
Reply | Report Abuse | Link to thisThis falls under the term "neat". What does a study of the life expectancy of women in a single part of the world in pre-industrial times tell us? Cant this be generated on data from the past 100 years for a much greater data set than one small country. As usual the title to the article is sensationalist and should more accurately read: "One Study, that is not representative of current lifestyles, Shows that Women May Live Slightly Longer if They Do Not Have Boys."
Reply | Report Abuse | Link to thisCan you elaborate?
Reply | Report Abuse | Link to thisThis is completely anecdotal, but my son was heavier than my daughter (he was 9 lbs, she was 7 lbs 4oz) and he ate WAY more than she did, and more frequently. It was totally exhausting to be a working, breastfeeding mom for a kid who ate as much as he did. I introduced cereal "early" (with the pediatrician's OK) because he was such a big eater.
Reply | Report Abuse | Link to thisAt 4, he's an extremely solid (not fat) little boy who runs me and his dad ragged. I am very happy to have had the chance to raise a boy. Years off my life? Who cares, if they're the ones at the end?
I agree with cookchh. Sound like voodoo statistics to me.
Reply | Report Abuse | Link to this0 sons = lives 33.1 years after last birth
Reply | Report Abuse | Link to this6 sons = lives 32.4 years after last birth
That is a TOTAL reduction of barely more than 2%. If the reduction was 7% PER son, the woman bearing 6 sons would have lived only 19.2 years after the last birth.
Doesn't anyone down there do any math to verify claims?
What about epigenetic changes to the mother because of the crossover of her sons' genetic material into her body which has been shown scientifically to occur?
Reply | Report Abuse | Link to thisIsn't it because daughters are more likely than sons to stay home and take care of their mothers in old age, especially when her husband is deceased?
Reply | Report Abuse | Link to thisIt's most likely an error in statistical methodology. Perhaps something similar to Satoshi Kanazawa's "Engineers have more sons, nurses have more daughters” that was debunked by Andrew Gelman a few years ago. See http://andrewgelman.com/2006/04/28/amusing_example/
Reply | Report Abuse | Link to thisHi, I am sorry but this is more"science of the Minute" than actual verified due diligence "REAL SCIENCE" I grew up in North Eastern PA. My Mom is 86 had 4 sons neighbor acrosss the street still alive at 92 3 boys
Reply | Report Abuse | Link to this5 more women at my Mom's church all mid 80's early 90's 3 or more sons. Small studies really can just abouot useless sometimes because "statistics can be manipulated to show just about anything" How about these Finnish women are more exposed to a greater number of toxins or any number of other more complex parts of living, giving child birth & life expectancy.
This is what we really call "Junk Science" letter grade D-
Thank you for putting the dimension of correlation forward.
Reply | Report Abuse | Link to thisI immediately doubt the abilities of any researchers that ignore the danger of confirmation bias and jump right to causation, rather than restrain themselves to reporting findings without undue attribution to supposed causes.
Yes. Funny statistics. Heading made to grab attention (and it did get mine), but basically the article tells us that instead of dying at 70.1 years (if a woman had no male children) a woman would die at 69.7 years (if she had six (!) male children) and lived in pre-industrial Finland. Mmmm...
Reply | Report Abuse | Link to thisSmells like junk science to me. If there is actually a small difference (which I doubt) it is most likely a culturally induced difference having something to do with this specific rural culture in this specific time and place. I doubt it has any general meaning.
Reply | Report Abuse | Link to thisYou may have noticed that the main stream press has been hyping this study.
My experience with Indian women is different. My mother lived till98.My motherin law's moher lived till 99. A friends' Grand Ma 103. and many moe examples with me.
Reply | Report Abuse | Link to thisThat is also assuming that both women are the same age.
Reply | Report Abuse | Link to thisi.e. both women are 24 and one has 6 sons while the other has??? 6 daughters? 2 daughters? no children?
OR
24 with 6 sons and living 32.4 years after last birth versus 18 with 2 daughters and living 33.1 years beyond last birth.
Also, keep in mind that Scandanavian countries tend to be very misandric. It is highly likely that this is nothing more that some "Go Team Woman" garbage with the outcome concluded BEFORE any data was even gathered.
I wonder if having daughters shortens the man's life expectancy?
Reply | Report Abuse | Link to thisHa! That's funny. We need science to tell us males are more of a stress on their mothers than females?
Reply | Report Abuse | Link to thisDid anyone bother to look at the social aspect? Daughters tend to care for their aging parents more intimately and emotionally than sons.
Reply | Report Abuse | Link to thisthis appears to be "junk science" and not worth my time opening up to read!
Reply | Report Abuse | Link to thisAny pregnancy carried to term has a higher mortality and morbidity than not being pregnant, although breast, ovarian, and endometrial cancer incidence are higher in women that never became pregnant; data in the article look as not surprising at all, the more times you enter a situation with an implicit danger, the more your chances of receiving harm are, thus the whole set of subjects having had the risk factor would have a reduced life expectancy respect to those never having this specific "risk factor"; is up to the women deciding if becoming pregnant or not and if having offspring is worth the risks involved, in any case, prematures with very low birthweight are today perfectly viable, and a induced delivery earlier in pregancy may reduce pregnancy-associated risks; the ethics of these decissions are out of my scope and knowledge, but of course, they're ethical issues in this, as in any field of life connected to human reproduction.
Reply | Report Abuse | Link to this