Does Excess Body Fat Maintained After the Seventh Decade Decrease Life Expectancy?

Pramil N. Singh, DrPH; Ella Haddad, DrPH; Serena Tonstad, MD, PhD; Gary E. Fraser, MD, PhD

Disclosures

J Am Geriatr Soc. 2011;59(6):1003-1011. 

In This Article

Abstract and Introduction

Abstract

Objectives: To determine whether the attenuation in risk of death due to excess body fat seen in most studies of older adults may be due to confounding, the relationship between adiposity and mortality was examined in adults who never smoked, were free of major chronic diseases, and maintained stable weight over long periods.
Design: Prospective cohort study.
Setting: The Adventist Health Study and Adventist Mortality Study in California.
Participants: Six thousand thirty adults aged 25 to 82 who had never smoked and had no history of coronary heart disease, cancer, or stroke.
Measurements: During 29 years of follow-up, anthropometric data were collected at baseline and 17 years later, and mortality surveillance continued for 12 years thereafter. Data were analyzed using survival analysis with attained age as the time variable.
Results: Instantaneous hazard plots indicated that men with a body mass index (BMI) greater than 22.3 kg/m2 and women with a BMI greater than 27.4 kg/m2 had a greater mortality risk through the ninth decade than those with lower BMI. For men aged 75 to 99 who maintained stable body weight, a BMI greater than 22.3 kg/m2 was associated with a 3.7-year (95% confidence interval (CI)=1.1–6.3) shorter life expectancy and significantly greater mortality (hazard ratio (HR)=1.88, 95% CI=1.16–3.04, for BMI=22.3–27.3 kg/m2; HR=2.00, 95% CI=1.01–3.97 for BMI>27.3 kg/m2; reference, BMI≤22.3 kg/m2). For women aged 75 to 99 who maintained stable body weight, a BMI greater than 27.4 kg/m2 was associated with a 2.1-year (95% CI=0.5–3.8) shorter life expectancy and significantly greater mortality (HR=1.12, 95% CI=0.80–1.58 for BMI<20.6 kg/m2; HR=1.41, 95% CI=1.05–1.89 for BMI>27.4 kg/m2; reference, BMI 20.6–27.4 kg/m2).
Conclusion: Excess body fat maintained after the seventh decade decreases life expectancy but appears to be less lethal in women.

Introduction

Although numerous prospective studies of middle-aged adults identify greater mortality due to overweight and obesity,[1] studies of older adults have long indicated that the risk due to current overweight or obesity attenuates[2–15]—often to the point of indicating equivocal or even lower mortality risk than being lean. Data from elderly cohorts have even been used to question whether current overweight and obesity remains an important risk factor after the age of approximately 75.[6,12] Overall, a causal interpretation of the attenuated risk in older adults remains controversial and has been recently debated because of the increasing prevalence of obesity-related diabetes mellitus in older adults.[16,17]

Data supporting an attenuation of the risk due to excess body fat with age come primarily from prospective studies that relate a single, baseline measure of body mass index (BMI) to mortality risk during follow-up.[2–15] The use of a single measure of BMI raises several methodological concerns. First, if obesity in healthy adults increases risk of developing disease that involves large weight loss, then the true contribution of obesity to this risk may be obscured if body weight is measured after disease onset. For example, in the Adventist Mortality Study,[18,19] a BMI of 30.0 kg/m2 was associated with a 50% lower risk of fatal respiratory disease, but after exclusion of those who experienced large weight loss during follow-up, a 100% greater risk for a BMI of 30 kg/m2 emerged. Second, attenuation of the relation between obesity and mortality with age could be evidence of greater measurement error of the index that occurs because of an age-related loss of fat-free mass—an effect that results in older adults having greater fat mass than younger adults of the same BMI.[20,21] If this bias due to age-related changes in body composition is different across levels of BMI, then risk estimates for higher BMI could attenuate with age.[21]

Can these methodological concerns be addressed in prospective investigations that relate BMI to survival? The effect of disease-related weight loss could be captured in a prospective study with multiple measures of body weight during follow-up. The effects of age-related changes in the relative amount of fat mass are more subtle and may not be detected according to BMI. In this context, large gains in body weight in older adults will be almost entirely attributable to increases in fat mass. Therefore, the use of weight gain during old age as a measure of adiposity can potentially provide more insight into whether excess body fat is a risk factor in older adults.

The purpose of this study was to examine whether excess body fat present after the seventh decade remains a risk factor for mortality in healthy adults. A prospective cohort study was conducted in which weight stability (fluctuation <5 kg) and weight gain over 17 years were related to the 29-year risk of mortality in 6,030 men and women who never smoked cigarettes and had no history of coronary heart disease, cancer, or stroke. The study's focus on weight stability addressed confounding by disease-related weight loss. To account for age-related changes in body composition, the effect of weight gains at middle age and older age were studied.

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