Harvard Mental Health Letter

In Brief: BMI and suicide

In Brief

BMI and suicide

Swedish researchers have found that the thinner a man is in youth, the more likely he is to kill himself later in life. They counted suicides among more than a million men whose height and weight were measured at age 18 during a mandatory call-up for military conscription. At that time, their average Body Mass Index or BMI — a standard measure of weight/height ratio — was 21.8 (18 to 25 is considered normal). Of the 1,300,000 men examined over a 30-year period (1968–1999), about 3,000 (0.24%) had committed suicide.

The risk decreased steadily as BMI increased. On average, each five-point increase in BMI was associated with a 15% lower risk of suicide. An obese man (BMI > 30) was only 85% as likely, and a thin one (BMI < 18) was 17% more likely to commit suicide when compared to a man of average height and weight — regardless of height, social class, parents' education, or the year of the examination.

The correlation was also the same whether the suicide occurred soon after the original measurement or more than 10 years later. So there was no evidence that, say, depression had made some men both thin (through appetite loss) and suicidal. Since there is also no reason to believe that being thin in itself is conducive to suicide, the authors suggest that low BMI and suicidal inclinations have a common underlying cause. Low levels of the neurotransmitter serotonin are linked to impulsive aggression, including suicide. The authors mention evidence that serotonin levels are increased by insulin resistance, which is linked to high BMI, and decreased by low cholesterol, which is associated with low BMI. But they admit that at this point any explanation is speculative, especially since their findings, so far, apply only to men.

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