Body mass index (BMI) may not increase mortality in overweight, according to a new study published in the open access journal PLOS ONE.

The number of overweight and obese people has increased dramatically over the past 25 years, and it is known that increased BMI can contribute to various cardiometabolic diseases.

However, the studies that have analyzed the association between BMI and total mortality have been contradictory. Most US studies used data from the 1960s to 1990s.

In the new research, scientists retrospectively studied data from 554,332 US adults, drawn from the 1999-2018 National Health Interview Survey and the 2019 US National Death Index.

BMI was calculated based on participants’ self-reported height and weight.

Information on demographics, social and behavioral factors, comorbidities, and access to health care was also available. On average, participants were 46 years old, half were female, and 69% non-Hispanic white.

35% had a BMI between 25 and 30, which is usually defined as overweight, and 27.2% had a BMI of 30 or more, which is defined as obese.

During a median follow-up of nine years and a maximum follow-up of 20 years the researchers identified 75,807 deaths. All-cause mortality risk was similar across a wide range of BMI categories. For older adults with a BMI between 22.5 and 34.9 there was no significant increase in mortality. For younger adults there was no significant increase in mortality in those who had a BMI between 22.5 and 27.4.

Overall for them obese adults, that is, with a BMI of 30 or more, there was a 21% to 108% increased risk of mortality attributable to their weight. The patterns observed remained largely the same in men and women and across races and ethnicities.

The researchers conclude that a BMI in the overweight range is not generally associated with an increased risk of all-cause mortality. “The study highlights growing reservations about using BMI alone to make clinical decisions. There is no clear increase in total mortality across a range of traditionally normal and overweight BMIs. However, this does not mean that morbidity is similar across these BMI ranges. Future studies should assess the incidence of cardiometabolic morbidities,” the researchers note.

See the scientific publication here