Firstborn of young mothers live longer

We've all read or heard about birth order and its effect on our behaviors: the firstborn is the most sensitive, the youngest excels in school, the middle child craves attention, etc.

A recent study offers a different twist: it suggests that the firstborn child of mothers under the age of 25 are almost twice as likely to live longer than the average life span and eventually become a centenarian (someone 100 years or older).

University of Chicago's Center for Aging recently published a study that examined the family histories of 991 American centenarians born from 1875 to 1899. The study, led by Leonid Gavrilov, found that firstborn children of mothers under the age of 25 were 1.7 times as likely to reach their 100th birthday than other children.

More specifically, the study found:

• firstborn daughters are three times more likely to survive to age 100, compared to later-born daughters of higher birth orders (7 and beyond)
• firstborn sons are twice more likely to become centenarians compared to sons having birth order between four and six

Comparisons of centenarians with their siblings found that the protective effect of being firstborn is due mostly to the mother's younger age at the child's birth (being born to a mother younger than 25 years).

Details of this study will be published in the January 2007 issue of the North American Actuarial Journal.