Monday, July 9, 2012

If you're 100, better odds you were born in the fall

In what seems like a bizarre bit of trivia, new research indicates that people born from September to November have the best chance of living to 100 or older.

At least that’s the case for people who are now very old. It may not be as much the case for folks born more recently than the mid-1950s or so. 

And it may not be a useful predictor very long after birth. A lot of the mortality that leads to the preference for fall-born kids may occur among the very young—perhaps within the first few months of life.

It may be useful to look at the numbers backward: Kids born in early summer—May, June and July, are far less likely than average to be represented among centenarians.

This data comes from researchers who have previously done Hawai`i work, although this particular research is not Hawai`i-specific. They are Leonid A. Gavrilov and Natalia S. Gavrilova, of the University of Chicago’s Center on Economics and Demography of Aging. 

The Gavrilovs conclude that “earlylife environmental conditions may have long-lasting effects on human aging and longevity.”

Their paper, Season of Birth and Exceptional Longevity: Comparative Study of American Centenarians, Their Siblings, and Spouses, was published in the Journal of Aging Research. They looked not only at U.S. data, but found similar patterns in Europe, where the required birth and life data are available. The paper is available here

Aging is of interest to Hawai`i in part because Hawai`i folks live longer than most:  Island residents can expect to live to 81.5 years, more than in any other state. Our previous post on the Gavrilov’s research is here

The new research suggests a number of reasons for the seeming anomaly favoring fall-born elders. 

The authors suggest it could be associated with maternal nutrition (summer-born kids were in utero during the harsh winter deprivations.) Temperature (avoiding extremely high summer temperatures or extremely low deep winter temperatures  in the first month of life.)  The “deadline hypothesis” (fall-born kids were older and therefore more advanced at the start of school, gaining an education advantage on their peers that rolls into better lifelong nutrition and opportunity and a healthier life.)

And it may also be that certain infectious diseases affecting the very young are more likely to hit summer-born kids. A powerful data point is that kids born in the fall don’t die of infections disease at as high a rate as their siblings.

“According to the USA statistics, mortality below age one month in 1940 was the lowest in September–November suggesting lower infectious load during this period of the year, because most infant deaths in the past were caused by infections,” the authors wrote.

© Jan TenBruggencate 2012

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