Anorexia of aging: physiologic and pathologic:
Despite the increase in body fat and obesity that occurs with aging, there is a linear decrease in food intake over the life span. This conundrum is explained by decreased physical activity and altered metabolism with aging. Thus, older persons fail to adequately regulate food intake and develop a physiologic anorexia of aging. This physiologic anorexia depends not only on decreased hedonic qualities of feeding with aging (an area that remains controversial) but also on altered hormonal and neurotransmitter regulation of food intake. Findings in older animals and humans have provided clues to the causes of the anorexia of aging. An increase in circulating concentrations of the satiating hormone, cholecystokinin, occurs with aging in humans. In addition, animal studies suggest a decrease in the opioid (dynorphin) feeding drive and possibly in neuropeptide Y and nitric oxide. The physiologic anorexia of aging puts older persons at high risk for developing protein-energy malnutrition when they develop either psychologic or physical disease processes. Despite its high prevalence, however, protein-energy malnutrition in older persons is rarely recognized and even more rarely treated appropriately. Screening tools for the early detection of protein-energy malnutrition in older persons have been developed. Multiple treatable causes of pathologic anorexia have been identified. There is increasing awareness of the importance of depression as a cause of severe weight loss in older persons. Approaches to the management of anorexia and weight loss in older persons are reviewed. Although many drugs exist that can enhance appetite, none of these are ideal for use in older persons currently.
Anorexia in older persons: epidemiology and optimal treatment:
Anorexia and weight loss are common findings in older persons. Over a life-time, normal persons decrease their food intake to counterbalance the decrease in physical activity and resting metabolic rate that occurs with aging. This physiological anorexia of aging increases the propensity to develop pathological anorexia and weight loss when an older person develops either a medical or psychological illness. The physiological anorexia of aging is due to a decreased opioid (dynorphin) feeding drive and an increase in the satiating effect of the gastrointestinal hormone, cholecystokinin. Nitric oxide deficiency may play a role in the early satiation commonly seen in older persons. A variety of social, psychological and medical conditions can lead to pathological anorexia. Depression is the most common cause of weight loss and anorexia in older persons. A number of conditions such as cancer and rheumatoid arthritis produce their anorectic and wasting effects by releasing cytokines. An idiopathic pathological senile anorexia has been characterised which also appears to be a cytokine-dependent syndrome. Early screening for malnutrition is a cornerstone of the management of anorexia; the Mini Nutritional Assessment is a well validated screening tool available for this purpose. Aggressive use of caloric supplements, enteral tube feeding and peripheral parenteral nutrition all have a role in the early management of anorexia. Numerous drugs (growth hormone, megestrol, cyproheptadine, tetrahydrocannabinol, anabolic steroids, prokinetic agents and antidepressants) have been utilised to treat the anorexia of aging with varying success.
Decreased food intake with aging.
There is a physiological decline in food intake with aging. The reasons for the decline in food intake are multifactorial and involve both peripheral and central mechanisms. Altered hedonic qualities of food occur due to alterations in taste and, more particularly, smell with aging. A decline in adaptive relaxation of the fundus of the stomach and an increased rate of antral filling appear to play a role in the early satiation seen in many older persons. Cholecystokinin levels are increased with aging and older persons are more sensitive to the satiating effects of this gut hormone. The decline in testosterone levels in older males leads to increased leptin levels and this may explain the greater decline in food intake with aging in the male. Within the hypothalamus, decreased activity of both the dynorphin (kappa opioid) and neuropeptide Y systems occurs in aging rodents. Cytokines are potent anorectic agents. Many older persons have mild inflammatory disorders that lead to anorexia. Exercise may increase food intake in older persons.
