Body Mass Index and Survival in Men and Women Aged 70 to 75

Leon Flicker, PhD; Kieran A. McCaul, PhD; Graeme J. Hankey, MD; Konrad Jamrozik, PhD; Wendy J. Brown, PhD; Julie E. Byles, PhD; Osvaldo P. Almeida, PhD

Disclosures

J Am Geriatr Soc. 2010;58(2):234-241. 

In This Article

Abstract and Introduction

Abstract

Objectives: To examine in an older population all-cause and cause-specific mortality associated with underweight (body mass index (BMI)<18.5), normal weight (BMI 18.5–24.9), overweight (BMI 25.0–29.9), and obesity (BMI≥30.0).
Design: Cohort study.
Setting: The Health in Men Study and the Australian Longitudinal Study of Women's Health.
Participants: Adults aged 70 to 75, 4,677 men and 4,563 women recruited in 1996 and followed for up to 10 years.
Measurements: Relative risk of all-cause mortality and cause-specific (cardiovascular disease, cancer, and chronic respiratory disease) mortality.
Results: Mortality risk was lowest for overweight participants. The risk of death for overweight participants was 13% less than for normal-weight participants (hazard ratio (HR)=0.87, 95% CI=0.78–0.94). The risk of death was similar for obese and normal-weight participants (HR=0.98, 95% CI=0.85–1.11). Being sedentary doubled the mortality risk for women across all levels of BMI (HR=2.08, 95% CI=1.79–2.41) but resulted in only a 28% greater risk for men (HR=1.28 (95% CI=1.14–1.44).
Conclusion: These results lend further credence to claims that the BMI thresholds for overweight and obese are overly restrictive for older people. Overweight older people are not at greater mortality risk than those who are normal weight. Being sedentary was associated with a greater risk of mortality in women than in men.

Introduction

Obesity is a global epidemic that is prevalent in developed and developing countries; affects people of both sexes and all ages; and has negative health consequences (ill health, disability, and mortality), economic costs, and social implications.[1] In industrialized countries, the prevalence of overweight and obesity in older people is a growing public health concern, particularly because sustained aging of their populations is expected to continue for many decades, and obesity and aging represent large components of healthcare spending.[1]

Based on the latest available data involving clinical measurements, Australia has the third highest prevalence of adult obesity of the Organisation for Economic Co-operation and Development countries (21.7% in 1999), behind the United States (34.3% in 2006) and the United Kingdom (24% in 2006).[2,3] Of older Australians, 28% of men and 38% of women aged 55 to 64 are obese, as are 22% of men and 32% of women aged 65 to 74 and 14% of men and 17% of women aged 75 and older.[4] The prevalence of obesity in older Australians tripled during the 20 years to 2004, representing a gain in weight of approximately 6 to 7 kg.[5]

Obesity and overweight are most commonly defined according to body mass index (BMI), also known as Quetelet's Index, a simple anthropometric measurement that is calculated by dividing body weight (in kg) by the square of height (in meters). The World Health Organization (WHO) defines the following four principal categories: less than 18.5 kg/m2=underweight; 18.5 to 24.9 kg/m2=normal weight; 25.0 to 29.9 kg/m2=overweight; and 30.0 kg/m2 or more=obese.[6] These thresholds were primarily based on evidence from studies of morbidity and mortality risk in younger and middle-aged adults, but it remains unclear whether the overweight and obese cut points are overly restrictive measures for predicting mortality in older people,[7] and concerns have been raised about encouraging apparently overweight older people to lose weight.[8]

Two systematic reviews and a meta-analysis of selected articles on BMI and mortality spanning 1966 to 2004 have concluded that BMI in the overweight range is not a risk factor for all-cause mortality in older people,[9,10] but methodological differences complicate the comparability of individual studies.

The objective of this study was to examine a major unresolved question;[11] what level of BMI is associated with the lowest mortality risk in older people? A secondary objective was to determine whether the relationship between BMI and mortality risk differed between older men and women. Two large representative population-based cohorts of community-dwelling older Australians, followed for a decade or until death (if sooner), were used. To the authors' knowledge, this is one of the most detailed studies of its kind conducted, particularly in people aged 70 and older.

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