It may sound crazy, but the preponderance of males in places where men live when they reach marriageable age influences how long they will live, according to a study published in the August issue of the journal Demography.
The researchers began by analyzing data from the Wisconsin Longitudinal Study, which tracked thousands of people who graduated from the state's high schools in 1957. The researchers were able to compare the proportion of boys in each man's graduating class to their age when they died (if they had). In this sample, the men who went to schools where boys outnumbered girls by more than 3-to-2 were about 40% more likely to have died by age 65 than men who went to schools where girls outnumbered boys by a similar margin.
Next, the researchers turned to Medicare and Social Security records for 12.7 million elderly white men. The researchers calculated the sex ratio among men and women of marriageable age (18-27 for men and 15-24 for women) in every state for each year from 1933 to 1948. They used that information to figure out how male-dominated each elderly man's environment was when he turned 20. Then they matched that up with their "survival in old age" and looked for a correlation, according to the study.
What they found was that those who came of age in states that were 52% male were slightly more likely to have died than men who came of age in states that were only 47% male. The difference amounted to shaving three months off the life expectancy of 65-year-old men, according to the study.
Dr. Nicholas Christakis of Harvard Medical School, who led the study, said there are at least three possible reasons why men who were surrounded by lots of other men might die younger:
- Perhaps the increased competition to find a wife made them feel more stress, which can have negative consequences for long-term health.
- The men might have had to wait longer to get married, which could be bad for their health. A number of studies have shown that spouses (especially wives) play a role in contributing to one another's health and survival.
- In places where men outnumbered women, the men (on average) had to settle for what the researchers described as a "lower-quality spouse," which could translate into less coddling and pampering from the wife and thus worse health.
The findings may not prompt an exodus from places like Madeline Plains, Calif.; Baldwin, Ill.; Brogan, Ore.; and Irving, Ill. (four cities where the population is at least 90% male). But Christakis said they may be a cause for concern for public health officials in countries where unbalanced sex ratios are a concern.
"Even if the men in those countries don't care about the trafficking and violence to women" that result from having an excess of men, he said, "policymakers might at least think about doing something because of the impact that it could have on the lifespan of men."