14 DAY TRIAL // A new analysis carried out by investigators from the National Cancer Institute (NCI) – part of the National Institutes of Health, and collaborators from a dozen other major research institutions worldwide, concluded that healthy non-smoking adults with a body mass index (BMI) between 20.0 and 24.9 have the lowest risk of early death.
The researchers also gave specific estimates of the risk of death among overweight and obese people.
They noted similar patterns of risk, even after they had accounted for differences in alcohol consumption, physical activity and education level: in all age groups, a BMI of over 25 increased the risk of death, even if the tendency was stronger for individuals overweight or obese before age 50.
At the beginning of each study, the researchers gathered data on BMI and other characteristics, through questionnaires filled in by the participants, while the causes of death were obtained from death certificates or medical records.
The review included only non-Hispanic white people, aged 19 to 84, but the investigators noted that the link between BMI and mortality risks can depend on racial and ethnic groups.
The analysis included data drawn from 19 long-term studies that were following their participants over periods of time varying from 5 to 28 years.
They concluded that healthy women who had never smoked and who were overweight, had 13% more risks of dying during the follow-up period than those with a BMI between 22.5 and 24.9; obese or severely obese women had an ever higher risk of death.
Participants with a BMI of 30.0 to 34.9 had a 44% increased death risk, those with a BMI of 35.0 to 39.9 had an 88% risk increase, and those whose BMI was 40.0 to 49.9 had a 250% (2.5 times) higher risk of death than women with a BMI of 22.5 to 24.9.
As for men, the results were very similar.
Overall, for men and women combined, every 5 unit rise in BMI meant a 31% increase in death risk.
Lead author of the study, NCI's Amy Berrington de Gonzalez, DPhil, said that “by combining data on nearly 1.5 million participants from 19 studies 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.
“Smoking and pre-existing 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.”
Obesity has become a global problem, and in the United States it is a leading public health concern, as two thirds of US adults are overweight or obese, and even worse, 17% of women and 11% of men are severely obese.
Obese people risk early death from heart disease, stroke and even certain cancers.
BMI is the most common way of measuring body fat and it is calculated by dividing a person's weight in kilograms by the square of his/her height in meters (kg/m2).
The US Centers for Disease Control and Prevention, and the World Health Organization define a BMI range between 18.5 and 24.9 as being normal.
People with a BMI of 25.0 to 29.9 are considered overweight, those with a BMI over 30.0 are obese and a BMI of 35 or higher characterizes severely obese individuals.
To calculate your BMI, go to http://www.nhlbisupport.com/bmi/bmicalc.htm.
The results of this review appear in the December 2, 2010, issue of the New England Journal of Medicine.