PARIS – Middle-aged adults with a body mass index of 25-29 kg/m2 had a significantly better adjusted survival during a median follow-up of nearly 10 years than did people with a “normal” body mass index of 20-24 kg/m2 in a worldwide study of more than 140,000. This finding suggests the current, widely accepted definition of normal body mass index is wrong.*
The new findings suggest that the current definition of a “healthy” body mass index (BMI) “should be re-evaluated,” Darryl P. Leong, MBBS, said at the annual Congress of the European Society of Cardiology. The analysis also identified a BMI specifically of 27 kg/m2 as associated with optimal survival among both women and men, “clearly outside the range of 20 to less than 25 kg/m2 that is considered normal,” said Dr. Leong, a cardiologist at McMaster University and the Population Health Research Institute, both in Hamilton, Ont.
Dr. Leong cited three potential explanations for why the new study identified optimal survival with a BMI of 25 to less than 30 kg/m2 among people who were 35-70 years old when they entered the study and were followed for a median of 9.5 years: The current study collected data and adjusted the results using a wider range of potential confounders than in prior studies, the data reflect the impact of contemporary interventions to reduce cardiovascular disease illness and death while past studies relied on data from earlier times when less cardiovascular disease protection occurred, and the current study included people from lower-income countries, although the finding is just as applicable to people who live in high-income countries, who were also included in the study population, noted Salim Yusuf, MBBS, principal investigator for the study.
A BMI of 20-24 kg/m2 “is actually low and harmful,” noted Dr. Yusuf in an interview. Despite recent data consistently showing better survival among people with a BMI of 25-29 kg/m2, panels that have recently written weight guidelines are “ossified” and “refuse to accept” the implications of these findings, said Dr. Yusuf, professor of medicine at McMaster and executive director of the Population Health Research Institute.
The results of the analyses that Dr. Leong reported also showed that BMI paled as a prognosticator for survival when compared with two other assessments of weight: waist/hip ratio, and even more powerful prognostically, a novel measure developed for this analysis that calculates the ratio of hand-grip strength/body weight. Waist/hip ratio adds the dimension of the location of body fat rather than just the amount, and the ratio of grip strength/body weight assesses the contribution of muscle mass to overall weight, noted Dr. Leong. He reported an optimal waist/hip ratio for survival of 0.83 in women and 0.93 in men, and an optimal strength/weight ratio of 0.42 in women and 0.50 in men. This means that a man whose hand-grip strength (measured in kg) is half of the person’s body weight has the best prospect for survival.
The study used data collected in PURE (Prospective Urban Rural Epidemiology Study) on 142,410 people aged 35-70 years from any one of four high-income countries, 12 middle-income countries, and five low-income countries. The study excluded people who had at baseline known coronary artery disease, stroke, heart failure, or cancer, and the adjusted analysis controlled for age, sex, region, education, activity, alcohol and tobacco use, and the baseline prevalence of hypertension and diabetes. During follow-up, 9,712 of these people died.
The researchers saw a nadir for mortality among people with a BMI of 25-29 kg/m2 for both cardiovascular and noncardiovascular deaths. In addition, the link between total mortality and BMI was strongest in the subgroup of people on one or more treatments aimed at preventing cardiovascular disease, while it essentially disappeared among people not receiving any cardiovascular disease preventive measures, highlighting that the relationship now identified depends on a context of overall cardiovascular disease risk reduction, Dr. Leong said. The results also showed a very clear, direct, linear relationship between higher BMI and both the incidence of diabetes and cardiovascular disease, as well as increased all-cause and noncardiovascular mortality among people with a BMI of less than 20 kg/m2.
Dr. Yusuf discussed the results of the analysis in a video interview.
The PURE study has received partial funding from unrestricted grants from several drug companies. Dr. Leong has been an advisor to Ferring Pharmaceuticals and has been a speaker on behalf of Janssen. Dr. Yusuf had no disclosures.
This story was updated 9/19/2019.