The Obesity Paradox in the Elderly: Potential Mechanisms and Clinical Implications
Section snippets
Methods
An extensive electronic search was conducted in MEDLINE (1966–January 2009), EMBASE (1988–January 2009), the Cochrane Library (1990–January 2009), and Web of Science (1900–January 2009) to retrieve research articles on obesity in older adults. Primary studies, review articles, letters, and commentaries were included. Reference lists of primary studies and review articles were also scanned. Key search terms were used: obesity, body mass, body mass index, body weight, weight, weight change, waist
Definitions and measurements
Several classifications of obesity exist. Some methods for measuring body composition, such as hydrostatic densitometry (underwater weighing), dual-energy x-ray absorptiometry, and near-infrared interactance, although accurate, require technologies and expertise that are not readily available.
BMI, calculated as body weight in kilograms divided by the square of the height in meters, is the most commonly used measure of obesity. Current American College of Cardiology and American Heart
Pathophysiology
The results from most studies demonstrate that energy intake does not change, or even declines with age.59 The age-related increase in fat mass is most likely caused by a decrease in energy expenditure. A decline in the resting metabolic rate and thermal effect of food (the rise in metabolic rate during digestion of food) and reduced physical activity contribute to the decrease in energy expenditure.60 This, combined with a stable energy intake, results in gradual fat accumulation. Hormonal
Association between BMI and mortality after age 65
In younger adults, there is strong evidence that obesity shortens the life span.64 Data from the American Cancer Society's Cancer Prevention Study65 have shown, however, that the relative mortality risk decreases with age (Fig. 1). This was also demonstrated in a 12-year prospective study of over 1 million Korean men and women (Fig. 2).66 An assessment of 13 observational studies from 1966 to 1999 by Heiat and colleagues,41 in which nonhospitalized people over 65 years were followed for at
Potential explanations for age differences in the relationship between BMI and mortality
Several explanations have been offered for the reverse epidemiology of obesity in the elderly (Table 3). Overweight and obese individuals who survive to old age may have characteristics that protect them from the adverse effects of being overweight or obese. This is known as the “survival effect.” Individuals who are susceptible to the complications of obesity may have already died, leaving behind those who are more resistant.
Another possible explanation for the obesity paradox is that the
Effect of obesity on morbidity, functional status, and quality of life in the elderly
Both cross-sectional and longitudinal studies have shown that a high BMI and increased abdominal fat are associated with metabolic changes even in older age.39 These changes include insulin resistance, dyslipidemia, and hypertension, which directly contribute to the development of metabolic syndrome, diabetes mellitus, and cardiovascular disease.92 In the systematic review by McTigue and colleagues,39 most studies reported a significantly increased risk of incident cardiovascular morbidity
Relationship between physical fitness, obesity, and mortality in the elderly
Physical inactivity and a low level of physical fitness are risk factors for all-cause and cardiovascular mortality.100 Low levels of physical activity and fitness have also been associated with obesity.100 A study of 831 male veterans101 showed a strong inverse relationship between exercise capacity (evaluated on a maximal exercise treadmill test) and mortality, independent of BMI. Another study of 35 middle-aged and elderly men and women102 showed that perceived physical fitness, but not BMI,
Effect of intentional weight loss on mortality in the elderly
Because of the potential benefits associated with being overweight or obese in old age, including prevention or delay in cognitive decline, protection from bone fractures, an increase in antioxidant defense, a reserve of fat and energy stores, and possibly an increase in longevity, there has been hesitation to recommend weight reduction in older adults. A recent systematic review by Bales and Buhr40 identified 16 studies on the effect of weight loss interventions in subjects 60 years of age or
Clinical implications
A summary of clinical implications follows:
- 1.
Obesity, as defined by BMI greater than or equal to 30 kg/m2, does not carry the same mortality risk in older adults (>60 years of age) as in younger adults. The association between BMI and mortality in older individuals is neutral or inverse. The current targets for normal BMI derived from epidemiologic studies of younger and middle-aged populations (BMI 18.5–24.9) do not seem to apply to the elderly. BMI should be used in conjunction with indices of
Summary
The prevalence of obesity is increasing at all ages, including the elderly. The complexity of measuring body fat and fat distribution in the clinical setting makes it difficult to determine the most valid, practical definition of obesity in the elderly population. In contrast to younger people, an overweight BMI is associated with lower mortality risk in the elderly. Similarly, an obese BMI does not confer increased risk of mortality in the elderly, although it is related to cardiovascular
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