No Increase in Mortality for Most With "Overweight" BMI, Study Says
Complete the form below to unlock access to ALL audio articles.
A new study that looked at data from more than half a million US adults over two decades suggests that body mass index (BMI) in the “overweight” range may not increase mortality independently of other risk factors, such as age. The research is published in PLoS ONE.
Understanding the impact of overweight and obesity
Overweight and obesity are on the rise, in developed as well as developing nations. One-third of US adults are overweight and over 2 in 5 adults (42.4%) are obese according to BMI scores.
What is BMI?
BMI stands for body mass index. It is a measure of a person’s weight and height – BMI score is calculated by dividing their weight in pounds or kilograms by the square of their height in feet or meters (BMI = weight/height2).
It is used by clinicians to broadly categorize if someone is a “healthy weight” for their height:
- Less than 18.5 – underweight.
- 18.5– 4.9 – the “healthy” range.
- 25–29.9 – overweight.
- 30–39.9 – obesity.
- 40 or over – severe obesity.
However, issues with the calculation of BMI have led to criticism as it does not account for muscle mass, fat distribution, bone density or racial and sex differences.
The use of BMI remains widespread despite its issues as it is a simple and cost-effective measure that correlates with several chronic diseases as well as death from any cause (all-cause mortality). Elevated BMI is linked to several cardio-metabolic diseases including coronary heart disease, high blood pressure, type 2 diabetes and some cancers.
Nevertheless, much of the information investigating links between BMI and mortality stems from 20th-century data predominantly coming from non-Hispanic White adults – meaning more modern and representative data are required to reassess these links. Rutgers University researchers Dr. Aayash Visaria and Professor Soko Setoguchi set out to address this topic.
Associations with mortality?
Visaria and Setoguchi studied data from 554,322 US adults, sourced from the 1998–2018 National Health Interview Survey and the 2019 U.S. National Death Index. The participants had an average age of 46 years, 50% were female and 69% were non-Hispanic White.
The researchers calculated BMI scores for the study population using self-reported height and weight information, then grouped them into nine categories based on their BMI scores.
Just over a third (35%) of participants had a BMI between 25 and 30, typically classified as overweight, meanwhile 27.2% of participants were defined as obese, with a BMI score equal to or greater than 30.
Subscribe to Technology Networks’ daily newsletter, delivering breaking science news straight to your inbox every day.Want more breaking news?
The researchers looked at the number of deaths in the study population, observing just over 75,000 deaths that occurred over a median follow-up of 9 years and a maximum follow-up of 20 years.
Interestingly, all-cause mortality was similar across a range of the studied BMI categories. Compared to the reference group with BMI scores of 22.5–24.9 (considered in the “healthy” range), there was no significant increase in mortality for older adults (65 years of age or older) with a BMI of 22.5–34.9, which extends into the “obese” range. Younger adults (20–64 years of age) with a BMI between 22.5 and 27.4 also had no significant increase in mortality.
Nevertheless, adults with a BMI of 30 or over had a 21% to 108% increased risk of mortality associated with their weight. Trends across the overall population were largely similar in men and women as well as across races and ethnicities.
Overall, the authors suggest that a BMI typically considered in the “overweight” range is generally not associated with heightened all-cause mortality independent of other risk factors. They also note that further studies including weight history, body composition and morbidity outcomes are needed to understand these findings in more detail.
“Our study highlights the increasing reservations of using BMI alone to drive clinical decisions,” said the authors. “There is no clear increase in all-cause mortality across a range of traditionally normal and overweight BMI ranges; however, that is not to say that morbidity is similar across these BMI ranges. Future studies will need to assess [the] incidence of cardio-metabolic morbidities.”
Reference: Visaria A, Setoguchi S. Body mass index and all-cause mortality in a 21st century U.S. population: A National Health Interview Survey analysis. PLoS ONE. 2023. 18(7): e0287218. doi: 10.1371/journal.pone.0287218
This article is a rework of a press release issued by PLOS. Material has been edited for length and content.
