The study itself is simple. The Dane Professor Esben Agerbo and his colleagues published a study in 2012 where they looked at 21,276 childless couples who in 1994 went to an in vitro fertilization clinic. All these women had problems conceiving. By 2005 a total of 96 women and 220 men died. Women who did NOT have a child were four times more likely to have died compared to those who did have a child. The inexplicable aspect of this study is that the same disadvantage also transferred to men. Men who remained childless in this study were twice as likely to die early.
How can this be explained? Gerontology theories predict that having children reduces your life expectancy--especially if you stop having sex afterwards--as most couple who have children tend to do.
The theory of antagonistic pleiotropy argues that some genes have contradictory effects at different age. Genes which might enhance your reproductive success--genes that increase testosterone in men, resulting in more muscle mass and masculine secondary sexual characteristics; or estrogen and bigger breasts in women--may at the same time have detrimental effects on survival later on in life--elevated risk of cancer in men and larger cancer nodes in women. Natural selection tends to favor these kinds of genes because they maximize the ability to transfer your genes—termed as fitness--without due concern for later life mortality. From this theory it follows that higher rates of reproduction comes at a cost of higher post-reproductive mortality.
As a complementary theory, the Disposable Soma Theory argues that there are metabolic trade-off between reproduction and longevity. Reproduction utilizes biological resources which could otherwise be used for physical maintenance. Having more children to bear and rear uses up limited physical resources that could have promoted better health and a longer life. In this view, higher reproduction is associated with a shorter life span.
These theories are supported by the numerous studies by demographers looking at nuns and monks. Overall, these studies have been showing reduced mortality of 31-11 percent among nuns and monks. An advantage that is generally larger for monks than for nuns. It is more a lifestyle that protects you from dying early (rather than promoting longer life.) In the real world, where people do not live in monasteries/nunneries and where they do not follow a regimented life, it is hard to separate what is causing people to die earlier.
In 2002, using data for a preindustrial Sami population in Finland, Samuli Helle and his colleagues showed that the number of sons--rather than the total number of children--affected women’s longevity. This association was also found in data from a 19th century Flemish village and confirmed the association between number of sons born contributing to their mother’s early age of death. However the effect was only evident among poorer women, and mainly for women whose sons survived to at least to age five. Leading to the conclusion that resource competition--rather than pregnancy--might be the main explanation. Having children is not only a biological event. There is also a financial cost associated between childbearing history and longevity.
Having four or five children shortened women’s life span after 50 by about 3.5 years compared to women with one child or less. However, this effect could only be found among the poorest women. No effect of number of children for more well-to-do women, or for men, could be found.
And the poorer you are the poorer your diet and the harder the competition for resources (both inside the womb and outside.)
How can this Danish study show such different results? Could we explain the results that having children increased longevity because it is reflecting having less money?
In Denmark, the first three courses of IVF are given free-of-charge. Wealthier couples, who may be able to buy more IVF treatment sessions can increase their chances of pregnancy. So methodologically, there is a higher likelihood that those who conceived were a self selecting richer group making the results already biased. What helped to clarify this point further--that it is socio-economic status which is promoting longer life rather than bearing children--is the finding that researchers found it didn't matter if the women or men who had children had them biologically or through adoption for them to benefit from increased longevity. Being well off is one of the main criteria for having successful adoption.
The longest person that ever lived, Jeane Lousie Clament had one daughter. But she also did not work, lived a life of leisure, smoked (until she was 117 years) and ate over a kilo of chocolate a week. If children should choose their parents wisely, then similarly parents need to make sure they can afford their children or else pay for it with their life.
© USA Copyrighted 2014 Mario D. Garrett