A study of 3.9 million adults published in The Lancet has found that being overweight or obese is associated with an increased risk of premature death. The risks of coronary heart disease, stroke, respiratory disease and cancer are all increased. Overall, the excess risk of premature death (before age 70) among those who are overweight or obese is about three times as great in men as in women.‌

On average, overweight people lose about one year of life expectancy, and moderately obese people lose about three years of life expectancy.

Professor Naveed Sattar, Professor of Metabolic Medicine at the University of Glasgow and co-author of the paper, said: “This work is important because the findings go against recent papers which seemed to suggest being overweight was associated with lowest risk of mortality.

“What we show, however, is that risks rise from much lower BMI and that being overweight and obese are associated with greater risks, and that at most BMIs, men have higher mortality risks than women.

“The very careful and robust methods of analyses used on the paper will also be useful for future researchers in this important area."

The World Health Organization estimates that 1.3 billion adults worldwide are overweight, and that a further 600 million are obese. The prevalence of adult obesity is 20% in Europe and 31% in North America.

“On average, overweight people lose about one year of life expectancy, and moderately obese people lose about three years of life expectancy,” added lead author Dr Emanuele Di Angelantonio, University of Cambridge.

“We also found that men who were obese were at much higher risk of premature death than obese women. This is consistent with previous observations that obese men have greater insulin resistance, liver fat levels, and diabetes risk than women.”

The study found an increased risk of premature death for people who were underweight, as well as for people classed as overweight. The risk increased steadily and steeply as BMI increased. A similar trend was seen in many parts of the world and for all four main causes of death.

Where the risk of death before age 70 would be 19% and 11% for men and women with a normal BMI, the study found that it would be 29.5% and 14.6% for moderately obese men and women. The authors defined premature deaths as those at ages 35-69 years.

The new study brings together information on the causes of any deaths in 3.9 million adults from 189 previous studies in Europe, North America and elsewhere. At entry to the study all were aged between 20 and 90 years old, and were non-smokers who were not known to have any chronic disease when their BMI was recorded. The analysis is of those who then survived at least another five years.

The authors say that assuming that the associations between high BMI and mortality are largely causal, if those who were overweight or obese had WHO-defined normal levels of BMI, then one in 7 premature deaths in Europe and one in 5 in North America would be avoided.

First published: 15 July 2016

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