New study identifies ideal body mass index

A study looking at deaths from any cause found that a body mass index (BMI) between 20.0 and 24.9 is associated with the lowest risk of death in healthy non-smoking adults. Investigators also provided precise estimates of the increased risk of death among people who are overweight and obese. Previous studies that examined the risks from being overweight were inconclusive, with some reporting only modestly increased risks of death and others showing a reduced risk. Also, the precise risks for different levels of obesity were uncertain.

03 dec 2010--The research team included investigators from the National Cancer Institute (NCI), part of the National Institutes of Health, and collaborators from a dozen other major research institutions worldwide. The results appear in the Dec. 2, 2010, issue of the New England Journal of Medicine.

BMI, the most commonly used measure for body fat, is calculated by dividing a person's weight in kilograms by the square of his/her height in meters (kg/m2). Current guidelines from the U.S. Centers for Disease Control and Prevention, and the World Health Organization define a normal BMI range as 18.5 to 24.9. Overweight is defined as a BMI of 25.0 to 29.9; obesity is defined as a BMI over 30.0; and severe obesity is defined as BMI 35 or higher. For a BMI calculator, go to http://www.nhlbisupport.com/bmi/bmicalc.htm.

Obesity has emerged as a leading public health concern in the United States. It has been well-established that people who are obese face increased risks of death from heart disease, stroke, and certain cancers. Currently, two-thirds of U.S. adults are overweight or obese. Even more worrisome, 17 percent of women and 11 percent of men are severely obese.

In this large analysis, investigators pooled data from 19 long-term studies designed to follow participants over time, from 5 to 28 years, depending on the study.

They found that healthy women who had never smoked and who were overweight were 13 percent more likely to die during the study follow-up period than those with a BMI between 22.5 and 24.9. Women categorized as obese or severely obese had a dramatically higher risk of death. As compared with a BMI of 22.5 to 24.9, the researchers report a 44 percent increase in risk of death for participants with a BMI of 30.0 to 34.9; an 88 percent increase in risk for those with a BMI of 35.0 to 39.9; and a 2.5 times (250 percent) higher risk of death for participants whose BMI was 40.0 to 49.9. Results were broadly similar for men. Overall for men and women combined, for every five unit increase in BMI, the researchers observed a 31 percent increase in risk of death.

"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," said NCI's Amy Berrington de Gonzalez, D.Phil., lead author of the study. "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."

The investigators observed similar patterns of risk even after accounting for differences in alcohol consumption, physical activity, and education level. The increased risk of death for a BMI of 25 or greater was also seen in all age groups, although it was more prominent for those who were overweight or obese before age 50.

The investigators gathered information about BMI and other characteristics from questionnaires participants completed at the beginning of each study. Causes of death were obtained from death certificates or medical records. This analysis was restricted to non-Hispanic whites aged 19 to 84. The investigators noted the relationship between BMI and mortality may differ across racial and ethnic groups. Other efforts are underway to study the effect of BMI on mortality in other racial and ethnic groups.

More information: Reference: Berrington de Gonzalez B, Hartge P, Cerhan JR, Flint AJ, Hannan L, MacInnis RJ, Moore SC, Tobias GS, Anton-Culver H, Beane Freeman L, W. Beeson L, Clipp SL, English DR, Folsom AR, Freedman DM, Giles G, Hakansson N, Henderson KD, Hoffman-Bolton J, Hoppin JA, Koenig KL, Lee IM, Linet MS, Park Y, Pocobelli G, Schatzkin A, Sesso HD, Weiderpass E, Willcox BJ, Wolk A, Zeleniuch-Jacquotte A, Willett WC, Thun MJ. Body-Mass Index and Mortality-- Prospective Analysis of 1.46 Million White Adults. Dec. 2, 2010, NEJM, Vol. 362, No. 23.

Provided by National Institutes of Health

Body Mass Index Alone Good Predictor of Mortality

BMI above or below the optimal range tied to higher risk of death

23 mar 2009-- Body mass index (BMI) is a strong predictor of mortality risk both above and below the optimal weight range of 22.5-25 kg/m², according to a report published online March 18 in The Lancet.

Members of the Prospective Studies Collaboration at the University of Oxford in the United Kingdom, conducted a review of 57 studies comprising 894,576 participants with a mean recruitment age of 46 years, predominantly in western Europe and North America.

In the period for which the investigators analyzed data, which excluded the first five years of follow-up, there were 66,552 deaths of known cause, which occurred within a mean of eight further years of follow-up, and at a mean age of 67 years. The lowest mortality rate was in the 22.5-25 kg/m² group, and there were positive associations between BMI and overall mortality, vascular, neoplastic, respiratory and diabetic, renal and hepatic mortality, the investigators found. Each 5 kg/m² BMI increase was associated with, on average, a 30 percent higher overall mortality. Below the 22.5-25 kg/m² range, BMI was inversely associated with overall mortality, mainly because of lung cancer and respiratory disease, the researchers report.

"Although other anthropometric measures (e.g., waist circumference, waist-to-hip ratio) could well add extra information to BMI, and BMI to them, BMI is in itself a strong predictor of overall mortality both above and below the apparent optimum of about 22.5-25 kg/m²," the authors write. "The progressive excess mortality above this range is due mainly to vascular disease and is probably largely causal."

Abstract

Higher BMI Linked to Increased Risk for Cancer

Increasing body mass index parallels risk for many cancers, according to a BMJ study released online.
British researchers examined data from the Million Women Study collected between 1996 and 2001. Some 1.2 million women, aged 50 to 64 at recruitment, were followed in national databases for an average of 5.4 years for cancer incidence and 7.0 years for mortality. By study's end, the researchers had found a significant increase in cancer risk per 10-unit increase in BMI for several cancers.
For example, in analyses adjusted for potential confounders, increasing BMI was associated with a relative risk for endometrial cancer of 2.89; for esophageal adenocarcinoma, 2.38; for kidney cancer, 1.53; for leukemia, 1.50; and for postmenopausal breast cancer, 1.40. For endometrial and esophageal cancers, the authors estimate that half the cases in postmenopausal women were due to overweight or obesity.
An editorialist notes that likely mechanisms for the association are the metabolic and endocrine effects of obesity.