Obesity in the elderly: More complicated than you think

Waist circumference is useful

In older adults, obesity can be diagnosed by a measurement such as waist circumference, which correlates highly with total fat and intra-abdominal fat.¹⁴ It is very cost-effective, simple, and useful for the office assessment of adiposity.

The measurement should be made halfway between the iliac crest and the lower anterior ribs, with the patient standing, and at the end of expiration.

The traditional standard for waist circumference is less than 89 cm (35 inches) for women and 102 cm (40 inches) for men. However, opinion differs, and different reference ranges exist depending on ethnicity. Additionally, because stature and body composition change with age, concerns have been raised about misclassification of the health risks related to obesity in older adults using the current standard.^15,16

The waist circumference is as good as or even better than the BMI as a measure of excess adiposity in older adults.^16–18 This is in part because of the age-dependent height decrease in older adults.^15,19 (Recall that the BMI is calculated using the height squared as the denominator; as a result, the BMI would give a higher reading and thus an overestimate of total body fat.) Conversely, we can underestimate the amount of adiposity because of decreases in abdominal muscle tone.¹⁷

Cutoffs for waist circumference should be age-specific.¹⁶

Investigators in the Netherlands^15,16 prospectively took 4,996 measurements in 2,232 people with a mean age of 70, from 1992 through 2006. They concluded that the best cutoffs for predicting the health risks of obesity in the elderly were 109 cm (43 inches) in men and 98 cm (39 inches) in women.

A group of researchers has proposed that the cutoffs be shifted upward in older adults, with new values for those age 70 and over.²⁰ The Health Survey for England aimed to describe the patterns and trends in waist circumference and abdominal obesity and overweight in people age 70 through 89, comparing both the standard and the new cutoffs. Optimal cutoffs recommended for abdominal obesity for patients age 70 and older were 100 to 106 cm in men and 99 cm in women.²⁰ Estimates of the prevalence of abdominal obesity are much lower using the new cutoffs.

SARCOPENIA: LOSS OF MUSCLE WITH AGE

With age comes sarcopenia—the progressive loss of muscle mass, primarily skeletal muscle, resulting in a decrease in strength and power.²¹ The process begins as early as the 20s or 30s.²² It is distinct from wasting (involuntary weight loss from inadequate intake), seen in starvation.²¹

Sarcopenia is defined as an appendicular skeletal muscle mass index (the appendicular skeletal mass divided by the square of the height in meters) of less than 2 standard deviations below a young adult reference, and a percentage of body fat over the 60th percentile for the individual’s sex and age.^23,24 Estimates of its prevalence vary, but it is common and it increases with age.^14,20

Sarcopenic obesity: Less muscle, more fat

Progressive loss of skeletal muscle with age, along with an increase and redistribution of body fat, is known as sarcopenic obesity.²⁵ It is associated with higher morbidity and mortality rates as well as a decline in functional strength, which leads to frailty.²³ This loss of muscle mass may go unnoticed in an older person until he or she begins to lose physical function.

As noted, in an older person with sarcopenic obesity, the BMI may mislead because of the high percentage of fat and the low lean mass.²⁶

Why we change with age

This change in body composition with age is a result of several factors. Illness or inactivity can lead to loss of muscle, while body fat is preserved.¹⁷ The combination of reduced physical activity, a lower resting metabolic rate, and an unchanged intake of food can increase the likelihood of sarcopenia.²⁷ Also possibly contributing are hormonal changes, including reduced production of growth hormone and testosterone and decreased responsiveness to thyroid hormone and leptin.²⁸

Moreover, the interaction of several factors can lead to a vicious circle of progressive loss of muscle and increase in fat. As people age, their physical activity tends to decrease, resulting in muscle loss. As muscle mass decreases, the amount of available insulin-responsive tissue is reduced, resulting in insulin resistance, which in turn promotes the metabolic syndrome and an increase in fat. With more fat, people produce more of the adipokines tumor necrosis factor alpha and interleukin 6, which further promote insulin resistance.

Other changes contribute to a decrease in muscle quality and performance, including an increase in intramuscular and intrahepatic fat, which is associated with insulin resistance.¹¹ The increases in adipose stores occur mostly in intra-abdominal fat rather than in subcutaneous fat.

ADVERSE EFFECTS OF OBESITY

A number of comorbidities arise with obesity, regardless of age.¹⁹

The diseases most strongly associated with obesity are the metabolic syndrome and type 2 diabetes mellitus.¹⁷ Studies have shown that in older adults, obesity as measured by waist circumference is associated with hyperglycemia and dyslipidemia.^29,30

Metabolic abnormalities may ensue in obese older people through complex mechanisms involving an age-related decline in sex hormones. For example, late-onset hypogonadism in men, which is more common in those who are obese, is related to the metabolic syndrome.²⁹

These mechanisms are also complex in women. Because estrogens can be produced in adipose tissue, obese postmenopausal women have higher concentrations of estrogens than their lean counterparts, and this may lead to metabolic abnormalities.³¹ (On the other hand, higher estrogen levels in obese menopausal women can protect against osteoporosis by increasing bone mass.)

Older people who weigh more and have more adipose tissue, especially those who became obese at a young age, have a greater risk of osteoarthritis of the knee,^32,33 which when combined with obesity can cause disability and physical impairment.¹⁹ And cardiovascular risk factors,^18,33 hypertension,³⁴ and certain cancers³⁵ are more common in older people with higher waist circumference.

THE OBESITY PARADOX

In general, obesity in younger adults has been shown to shorten life expectancy. This risk of death is often associated with obesity-related health problems.

In older people, the effect of obesity is much more complex.³⁶ The optimal weight in terms of survival increases with age. More interesting is the finding that although the risk of cardiovascular disease is higher in overweight or obese older adults, studies also suggest that in this age group, being overweight or obese is paradoxically associated with lower mortality rates from these diseases.²⁶ This phenomenon is called the obesity paradox.³⁷

For those over age 75, the relative risk of death from all causes and from cardiovascular disease has been found to decrease with increasing BMI.²⁵ The relationship between BMI and death from all causes in older adults may actually be a U-shaped curve, meaning that the risk of death rises at both extremes of BMI values.²⁶