All-Cause Mortality Risk and BMI

Elevated BMI (body weight in kilograms divided by height in meters squared) increases risk for heart disease and some types of cancer.  There is less data on the relationship and effect size on all-cause mortality.   A recent pooled study analysis of approximately 1.5 million adults in the U.S. provides important new data.

The authors of the study pooled (aggregated) 19 longitudinal studies of white (non-Hispanic) samples.    The large sample size allows for controlling for possible confounding variables.  The variables controlled in this study included:

• Alcohol intake
• Educational level
• Marital status
• Physical activity level
• Smoking status (current smoker, former smoker and never smoked)

The graph summarizes the findings for all-cause mortality.  The summary measure is the hazard ratio.  The death rates for those in the normal BMI range (20.0 to 24.9) is set at 1.0 and those in other weight ranges compared against this standard.   For example, a hazard ratio of 1.5 would indicate a 50% increase in risk of death during the follow-up period compared to the normal weight group.

The study found a progressive increase in mortality risk for those with increasing BMI.  The highest BMI group showed a hazard ratio of about 2.5.  Of note, those with low BMI also had higher mortality risk although not as great as for those in the highest BMI.   The authors broke down the cause of death into 3 groups: cardiovascular death, death due to cancer, and other causes.   Among those who never smoked, the highest BMI groups showed greater risk for cardiovascular death (HR 4.4), other causes of death (HR 3.0) and cancer deaths (HR 1.9).  The lowest BMI group (15.0-18.4) showed excess deaths in the other death causes category (HR 1.84) and cardiovascular death (HR 1.47).  Cancer deaths were not statistically higher in this low weight group.

The authors note that the low weight group risk for mortality may be an artifact of undiagnosed or presence of a disease not assessed in the study.   The hazard ratio in this low weight group was weaker among those with high physical activity (lean and fit) compared to those who were inactive and may have “illness-induced” wasting.  An interesting finding was that the lowest BMI had relative high rates of smoking (25%) compared to the other weight groups.  This association was controlled for in the analysis and the authors note, “we cannot rule out the possibility that being underweight is associated with increased mortality.”

 The authors note this study reflects findings in a relatively affluent white population and may not be generalizable to other populations.  The study underscores the need for public health measures to prevent obesity and improve the treatment success rates in those already significantly overweight.


If you would like to calculate your own BMI, you can use this link from the National Heart Lung and Blood Institute.

Graph of study summary findings is an original figure provided by Brain Posts.

Berrington de Gonzalez A, Hartge P, Cerhan JR, Flint AJ, Hannan L, MacInnis RJ, Moore SC, Tobias GS, Anton-Culver H, Freeman LB, Beeson WL, 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 (2010). Body-mass index and mortality among 1.46 million white adults. The New England journal of medicine, 363 (23), 2211-9 PMID: 21121834