Obesity Epidemiology

OBESITY AND MORTALITY 219because overall mortality is much higher in the elderly, the absolute increase in deathrates associated with higher BMIs was much greater in older people than in middle-agedindividuals 12 (Fig. 11.2). Thus, the reduced relative impact of obesity on mortality doesnot mean that obesity is not detrimental in the elderly.The declining relative impact of BMI on mortality with increasing age may alsoreflect several methodological issues: (a) greater bias due to higher prevalence of existingand occult chronic diseases in the elderly; (b) lower validity of BMI in measuring excessbody fat in older people; or (c) survival bias or depletion of the susceptible, whichrelates to the deaths of those most vulnerable to obesity-related complications. Thesedifficult methodological problems can affect the ability to obtain valid estimates of therelationship between BMI and mortality.Future research may address these problems in part by reporting both relative andabsolute risks associated with obesity. In addition, it is imperative to include measures ofbody fat distribution (discussed later). Moreover, it is important to evaluate the effects ofobesity on functional disability in older individuals. Data have shown that even thoughBMI has a diminished impact on mortality in individuals 65 years or older, overweightand obesity were associated with significantly increased functional disabilities. 13 Giventhe methodological issues related to BMI and mortality, public health guidelines for(A)3.030-64 YearsRelative risk2.52.01.565-74 Years75 Years1.023.0-24.925.0-26.926.5-27.928.0-29.930.0-31.932.0-34.935.0Body mass index(B)Risk difference(per 100,000)2,5002,0001,5001,00050030-64 Years65-74 Years75 Years023.0-24.925.0-26.926.5-27.928.0-29.930.0-31.932.0-34.935.0Body mass indexFigure 11.2 Risk of death associated with BMI among male nonsmokers without chronic healthconditions, according to age. The annual risk of death is expressed as both the RR (A) and the absoluteamount of additional risk (risk difference) (B) per 100,000 population, as reported in the AmericanCancer Society Cancer Prevention Study 2. Reproduced with permission from Byers T. Overweightand mortality among baby boomers—now we’re getting personal. N Engl J Med. 2006;355:758-760. 12