Such young men are significantly more likely to develop serious ill health including the risks of diabetes, potentially fatal blood clots, and heart attacks by the time they reach middle age, or not even make it that far, suggests research published in the journal British Medical Journal, BMJ Open.
It's well known that obesity in adulthood poses a risk for diabetes and cardiovascular disease, but it's not been clear whether obesity in early adulthood strengthens that risk.
All potential conscripts in Denmark are subjected to a battery of psychological and physical tests, including weight.
Most (83 per cent or 5407) were within the normal range and 5 per cent were underweight (353). One in 10 (639) were overweight and 1.5 per cent (97) were obese.
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Almost half of those classified as obese at the age of 22 were diagnosed with diabetes, high blood pressure, heart attack, stroke, blood clots in the legs or lungs, or had died before reaching the age of 55.
They were also more than twice as likely to develop high blood pressure, have had a heart attack, or to have died.
Every unit increase in BMI corresponded to an increased heart attack rate of 5 per cent, high blood pressure and blood clot rates of 10 per cent, and an increased diabetes rate of 20 per cent.
Obese young men were three times as likely to get any of these serious conditions as their normal weight peers by middle age, conferring an absolute risk of almost 50 per cent compared with only 20 per cent among their normal weight peers.