A Danish study reveals being underweight or at the lower end of “healthy” BMI may raise the risk of early death, while being slightly overweight may not shorten life. Findings challenge old assumptions about weight and health.
For decades, we’ve been told that keeping our weight in the “normal” range is the best way to live longer. But new research from Denmark is shaking up that belief, showing that being underweight—or even at the lower end of what’s considered “healthy”—may actually be more dangerous than carrying a few extra pounds.
The findings, presented at the European Association for the Study of Diabetes (EASD) conference in Vienna, suggest that people who are slightly overweight—or even mildly obese—may live just as long as those with an ideal BMI. In contrast, people who are underweight, or at the thinner end of the healthy range, face a much higher risk of early death.
What the Study Found
Researchers tracked more than 85,000 adults, most of them women in their mid-60s, over five years. Here’s what they discovered:
Underweight was the riskiest: People with a BMI below 18.5 were nearly three times more likely to die than those at the upper end of the normal range (22.5–<25).
Being on the thinner side of “healthy” was also concerning: Participants with BMIs between 18.5–20 had double the risk, while those in the 20–22.5 range had a 27% higher risk.
Overweight wasn’t as harmful as expected: Those with BMIs between 25–35—classified as overweight to mildly obese—were no more likely to die than the reference group.
Severe obesity did increase risk: A BMI of 40 or higher more than doubled the likelihood of death.
Why Would Lower Weight Be Riskier?
Lead researcher Dr. Sigrid Bjerge Gribsholt explains that illness may play a role. Sometimes, people lose weight because of underlying health problems, which makes low BMI look more dangerous than it really is.
Another key factor is where fat is stored. Fat around the abdomen (visceral fat) can trigger diabetes and heart disease, while fat in the hips and thighs is less harmful. This means two people with the same BMI could have very different health profiles.
Beyond the Number on the Scale
BMI is just one piece of the puzzle. Severe obesity still carries health risks, but being slightly overweight may not be the danger it was once believed to be—especially for older adults.
What matters most is overall metabolic health, fat distribution, and whether conditions like diabetes or high blood pressure are present. As Professor Jens Meldgaard Bruun puts it, “The treatment of obesity should be personalized.”
In other words, health isn’t defined by a single number. For many people, carrying a little extra weight might not shorten life—but being too thin just might.