A study spanning almost four decades and involving more than 100,000 adults in Denmark has found that those with an overweight' body mass index (or BMI) were more likely to live longer than those in the 'healthy', 'underweight', and 'obese' categories. The study, led by clinical biochemist Børge Nordestgaard from Copenhagen University Hospital, analysed the medical data of more than 100,000 adults in Denmark, recruited in three groups about 15 years apart. They found that during the four decades of analysis - from 1976 to 2013 - the BMI associated with lowest risk of death increased from 23.7 to 27. The study also found that those in the 'obese' category ended up having the same risk of death as those in the 'normal' range, even when factors such as age, sex, family history of disease, socio-economic status, and smoking were taken into account. This means that in the past 40 years, the weight category associated with the longest lifespan has gone from 'normal' to squarely in the 'overweight' camp, which suggests that either our classification for 'normal' weight is wrong, or the link between our weight and our overall health is far more complicated than we thought.