Insurers that want to sell life insurance to 80-year-olds should consider looking for first-born daughters of farmers who owned farms out west.[@@]

And it wouldn’t hurt if the women were born in January.

Natalia Gavrilova and Leonid Gavrilov have published figures supporting that strategy in a paper on centenarians released by the life insurance research committee at the Society of Actuaries, Schaumburg, Ill.

Gavrilova and Gavrilov, researchers at the University of Chicago, based their paper on analysis of records for 485 people born from 1890 to 1900 who lived to 100. The data came from Web-based genealogies, Social Security death records and census records.

Because of concerns about data quality, the researchers used data only for centenarians born in the United States.

The researchers also used census data to compare conditions in the homes of children who lived to 100 with conditions in other homes.

Women in developed countries tend to live longer than men do, and 76% of the centenarians included in the study were women, the researchers write.

Children of men who owned their own farms were about 60% more likely to reach 100 than children of tenant farmers, and children of farm owners were at least 4 times more likely to live to 100 than children of men who rented homes that were not attached to farms.

Geography also affected the chances that a child born in the late 19th century would live to 100: Children born in the West were about 3 times more likely than children born in the Northeast to become centenarians.

Girls born in the Midwest and South were about twice as likely as girls born in the Northeast to become centenarians, but the chances of a boy living to 100 were only about 40% better in the Midwest and only 11% better in the South.

Gavrilova and Gavrilov uncovered a complicated relationship between birth order and exceptional longevity.

First-born daughters outdo other women, and first-born sons also do well. But “seventh sons” really are lucky: Sons who have 6 or more older siblings are more likely to become centenarians than sons with 2 to 5 older siblings, and sons who are the ninth or 10th born are more likely to become centenarians than first-born sons are.

When the researchers looked at birth months, they found that 80-year-olds born in April and May have average life expectancies that are a few weeks below average and as much as 8 weeks below the average for 80-year-olds born in January.

“This stability is evident at least for the 1885-1899 birth cohorts,” the researchers write. “The fact that such an early circumstance of human life as the month of birth may have a significant effect 80 years later on the chances of human survival is quite remarkable. It indicates that there may be critical periods early in human life particularly sensitive to seasonal variations in living conditions in the past (e.g., vitamin supply, seasonal exposure to infectious diseases, etc.)”