Comprehensive Study Identifies Ideal Body Mass Index

A new study that examined deaths from any cause found a body mass index (BMI) between 22.5 and 24.9 is associated with the lowest risk of death in healthy non-smoking adults.

Researchers from the US National Cancer Institute (NCI; Bethesda, MD, USA), the Karolinska Institutet (Stockholm, Sweden), and a dozen other major research institutions worldwide pooled data from 19 prospective studies encompassing 1.46 million white adults aged 19 to 84 years of age (median age 58). The investigators gathered information about BMI and other characteristics from questionnaires the participants completed at the beginning of each study. Causes of death were obtained from death certificates or medical records.

The results showed that the median baseline BMI was 26.2. During a median follow-up period of 10 years, 160,087 deaths were identified. Among healthy female participants who never smoked, there was a J-shaped relationship between BMI and all-cause mortality. Overweight women were 13% more likely to die than those with a BMI of 22.5-24.9. Women categorized as obese or severely obese (BMI of 30-34.9) had a 44% increase in risk of death, while those with a BMI score of 35-39.9 had an 88% increase in risk. Participants with a BMI score of 40-49.9 had a staggering 2.5 times (250%) higher risk of death; the results were broadly similar for men. For men and women combined, for every five unit increase in BMI, the researchers observed a 31% increase in risk of death. The study was published in the December 2, 2010, issue of the New England Journal of Medicine (NEJM).

"We were able to evaluate a wide range of BMI levels and other characteristics that may influence the relationship between excess weight and risk of death,” said lead author Amy Berrington de Gonzalez, PhD, of the NCI. "Smoking and preexisting illness or disease are strongly associated with the risk of death and with obesity. A paramount aspect of the study was our ability to minimize the impact of these factors by excluding those participants from the analysis.”

BMI, the most commonly used measure for body fat, is calculated by dividing a person's weight in kilograms by the square of the height in meters (kg/m²). Current guidelines from the US Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO) define a normal BMI range as 18.5-24.9. Overweight is defined as a BMI of 25.0-29.9; obesity is defined as a BMI over 30; and severe obesity is defined as BMI 35 or higher.

Related Links:
US National Cancer Institute
Karolinska Institutet