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CHAPTER 13 The anorexia of aging
Neema Sharda1, Jantira Thomas2, and Ian M. Chapman3
1 Division of Geriatric Medicine, Duke University, Durham, North, Carolina, USA
2 Division of Geriatric Medicine, Wake Forest University, Winston‐Salem, North, Carolina, USA
3 University of Adelaide, Royal Adelaide Hospital, Adelaide, Australia
Introduction
In many older adults, the decrease in energy intake is greater than the decrease in energy expenditure, so body weight is lost. This physiological, age‐related reduction in energy intake has been termed anorexia of ageing.1 Undernutrition is common in older adults, with a significant impact on outcomes including physical function, healthcare utilization, and length of hospital stays.2–5 According to the World Health Organization, malnutrition refers to deficiencies, excesses, or imbalances in a person’s energy intake. Malnutrition encompasses both undernutrition and obesity6; in this chapter, malnutrition and undernutrition are used interchangeably. The Global Leadership Initiative on Malnutrition established that the diagnosis includes a phenotypic criteria (non‐volitional weight loss, low body mass index, or reduced muscle mass) and a etiologic criteria (reduced food intake or absorption, or underlying inflammation due to acute or chronic disease/injury).7 A key predictor of malnutrition in older adults is loss of appetite.8 The prevalence of malnutrition depends on the population, geography, and living situation. One study from 2010 reported a review of the Mini Nutritional Assessment across settings in Europe, the United States, and South Africa; the prevalence of malnutrition was 22.8% (n = 4507, mean age 82.3, 75.2% female), with the highest rates for patients in rehabilitation units (50.5%), less for hospitalized older adults (38.7%), and lower among community dwellers (5.8%).9 More recently, in 2016, a meta‐analysis on malnutrition in various European healthcare settings suggested the following malnutrition rates: 6.0% (95% CI 4.6–7.5); hospital, 22.0% (95% CI 18.9–22.5); nursing homes, 17.5% (95% CI 14.3–20.6); long‐term care, 28.7% (95% CI 21.4–36.0); rehabilitation/sub‐acute care, 29.4% (95% CI 21.7–36.9).10
As indicated in this chapter, (i) ideal weight ranges are almost certainly higher in older than younger adults; (ii) weight loss is often associated with adverse effects in the elderly, particularly if unintentional; and (iii) undernutrition manifesting as low body weight and weight loss is common in older adults and has significant adverse effects. Healthcare providers should maintain a high level of awareness to detect unintentional weight loss and undernutrition in this age group.
‘Ideal’ body weight in older people
There is increasing evidence that the adverse effects of being overweight or obese, as defined by standard body mass index (BMI) criteria, are not as great in the elderly as in younger adults.11 Ideal weight ranges based on life expectancy are higher for older than young adults. For example, in a 12‐year study of 324,000 people in the American Cancer Society Cohort, for people under the age of 75, there was a significant and progressive increase in subsequent mortality as baseline BMI increased above 21.9 kg−2. However, these adverse effects of increasing body weight diminished with increasing age above 45 years and were absent altogether over 75 years. Among 4736 people age 60 or more followed for an average of 4.5 years in the Systolic Hypertension in the Elderly Program (SHEP), those whose baseline BMI was in the lowest quintile (<23.6 kg−2) had the highest subsequent mortality and those within the highest BMI quintile (≥31 kg−2), corresponding to the conventional criteria of obesity, had the lowest mortality.12,13
Recommendations for ideal weight ranges in older people vary, but there is strong evidence that BMI values below about 22 kg−2 in people over 70 are associated with worse outcomes than higher weights, and BMIs below 18.5 kg−2 are a particular concern. The optimum BMI for survival in people over age 70 is probably in the range 25–30 kg−2, and there is some recent evidence that BMIs above ‘normal’ may be somewhat more protective in women than men.14
Although optimum body weight for older adults is higher than that for young adults, they tend to weigh less. The decline in body weight with age, as measured by BMI, has been well documented in population‐based, cross‐sectional, and longitudinal studies. For example, in the 1997–1998 US National Health Interview Survey of 68,556 adults, more people 75 and older than those 45–64 were ‘underweight’ (BMI <18.5; 5 vs. 1.2%) and substantially fewer were ‘overweight’ (BMI >25; 47.2 vs. 63.5%).15,16
Weight loss in older people
The lower average body weight of older than younger adults is not a function of survival from obesity‐related diseases. On average, people over 75 years of age are more likely to lose than gain weight. For example, in a study that followed 247 community‐dwelling American men age over 65 for two years, men lost on average 0.5% of their body weight per year, and 13.1% of the group had involuntary weight loss of 4% per annum or more. Numerous studies have shown that weight loss in the elderly is associated with poor outcomes, certainly if involuntary, but possibly even when deliberate. The prospective Cardiovascular Health Study, for example, studied 4714 home‐dwelling subjects over 65 without known cancer. In the three years after study entry, 17% of the subjects lost 5% or more of their initial body weight, compared with 13% who gained 5% weight or more. The weight‐loss group had significant increases in total (2.09 × ↑ [95% CI 1.67–2.62]) and risk‐adjusted mortality (1.67 × ↑ [95% CI 1.29–2.15]) over the following four years compared with the stable weight group. The increased mortality occurred irrespective of starting weight and whether or not the weight loss was intentional. The weight gain group had no increase in mortality. In the SHEP study mentioned above, subjects who had a weight loss of 1.6 kg per year or more experienced a 4.9 times greater death rate (95% CI 3.5–6.8) than those without significant weight change. Although mortality was also increased if weight increased more than 0.5 kg per year, the increase was less than that with weight loss (2.4‐ fold vs. 4.9‐fold increase). Of particular note, the adverse effects on mortality of weight loss were present even in the subjects who were heaviest at baseline (BMI ≥31) and were independent of baseline weight. The combination of initially low body weight and weight loss carries a particularly poor prognosis.