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Thin men may be more likely to attempt suicide than those who are overweight, according to a new study that confirms a puzzling link between body weight and suicide risk.
The first investigation to find a link between body mass index (BMI) and suicide risk was conducted in the US in 1966, and studies since then have been largely consistent in showing that as body weight climbs, suicides decline.
Most of that research has focused on men, but the same pattern has been seen among women.
It's a perplexing connection, researchers say, since some studies have found heightened rates of depression among obese adults, and because obesity is tied to physical health problems like heart disease and diabetes.
This latest look at the question, reported in the American Journal of Epidemiology, is also the largest - a decades-long follow-up of more than 1 million Swedish men who had physical exams for the military draft sometime between 1969 and 1994.
Early-adulthood BMI
Researchers used those records to calculate the men's early-adulthood BMI - a measure of weight in relation to height - and used Sweden's national hospital discharge register to track any suicide attempts in the group up to 2006.
Over an average follow-up of 24 years, 18,277 men - or 1.6% of the group - were admitted to a hospital for a suicide attempt.
The suicide attempt rates according to body weight showed only small absolute differences: among underweight men, 2% attempted suicide during the study period, compared with 1.6% of normal-weight men and 1.5% of those who were overweight.
But the researchers did see a clear pattern linking BMI and the relative risk of attempted suicide: overweight and obese men were 12% less likely to attempt suicide than normal-weight men were, whereas underweight men were 12% more likely. That was with factors including age, education level and income taken into account.
In addition, when the researchers looked at the full range of BMI, they found that even among normal-weight men, the odds of suicide dipped with incremental BMI changes. The pattern was evident among men who were free of depression at military conscription, and remained when the researchers factored in new diagnoses of depression during the follow-up period.
Reasons remain murky
While the findings back up previous research, the underlying reasons remain uncertain, according to the researchers, led by Dr Finn Rasmussen of the Karolinska Institute in Stockholm.
With men, they speculate, one possibility is that some of those with a low BMI are dissatisfied with their bodies to an extent that could affect their odds of suicide attempt. Among men, particularly young men, a higher BMI can reflect greater muscle mass, rather than fat. A low BMI, in contrast, may be out of the range that many men consider "ideal."
An open question is whether the connection between BMI and suicide reflects a sort of "reverse causality" - that is, depression or physical illness, such as cancer, causes people to lose weight and also raises their relative risk of suicide attempt.
Another possibility is a biologic mechanism involving insulin, which can influence mood by affecting brain concentrations of the signaling chemical serotonin. "Suicide risk has been shown to increase with increasing numbers of insulin sensitivity markers, including low BMI," the researchers write. But they did not have enough data on the subjects' insulin status to examine that theory.
Study focused on young men
A major strength of this study is that it focused on young healthy men, whose low BMI would be unlikely to reflect any underlying illness, said Dr Kenneth J. Mukamal of Harvard University and Beth Israel Deaconess Medical Center in Boston.
It's still possible that depression plays some role in the BMI-suicide link, according to Mukamal, who wrote an editorial published with the study. The researchers tried to factor in depression rates during the study period; however, they only had records on hospitalisations for depression, which does not capture all cases, Mukamal noted in an interview.
Untangling the relationships between depression, body weight and suicide risk is difficult, he said. And it would take long-term studies with repeated measures of weight, depression symptoms and depression treatment to tease apart the effects of each on suicide risk.
Weight has greatest impact on fatal suicides
Mukamal speculated that body weight may actually have its greatest impact on fatal suicides, rather than suicide attempts.
He pointed out that an earlier study of this same group of Swedish men focused on suicide deaths. Combining data from the earlier and current reports shows that thinner men had a higher proportion of successful suicide attempts.
It's possible, Mukamal said, that thinner men are more likely than overweight men to choose suicide methods that require more physical ability and are more lethal - such as hanging or jumping to their deaths.
Another possibility, he said, is that drug overdoses are less likely to be fatal for heavier men, since larger bodies require larger doses to be deadly.
Potential for prevention
So if thinner people are at increased risk of suicide, what does it mean?
Clearly, Mukamal said, no one would start advocating that people gain weight in order to lower their suicide risk.
"This association is well studied and well established now. The question is, what do we do with it?" he said.
According to Mukamal, one implication is that, if heavier weight affects suicide risk mainly by making attempts less lethal, then that reinforces the importance of limiting people's access to those more-fatal means.
That, he said, could mean restricting people's access to high bridges or ability to quickly buy a gun. He also noted that in the UK, a move to reduce the number of pills in packages of the painkiller acetaminophen seems to have met with some success in reducing the likelihood of fatal overdoses.
"A measure as simple as that can make a difference," Mukamal said. (Reuters Health/ October 2010)
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