A hormone known to suppress appetite is more abundant in seniors than in young adults and has a greater effect in squelching hunger in elderly people, scientists report. The findings suggest that counteracting this hormone–called cholecystokinin, or CCK–could help elderly people regain a healthy appetite and avoid anorexia, a condition of dangerous weight loss.
Various cells, notably those lining the entry to the small intestine, secrete CCK. Food settling into the lower stomach stimulates the intestinal cells to release the hormone, and CCK then activates the pancreas and gall bladder to produce digestive juices. This release and other CCK provided by nerve cells play a part in shutting off hunger signals. Studies show that giving animals extra CCK can inhibit appetite.
To look for this mechanism in people, researchers at the University of Adelaide in Australia monitored the diet of 12 elderly people and 12 young adults on three nonconsecutive days. These healthy participants fasted overnight and then ate meals prepared for them at a test facility. At each meal, the volunteers were offered more food than they could eat, says study coauthor John E. Morley, a geriatrician and endocrinologist at St. Louis University Health Sciences Center, who collaborated with the Australian team.
Before eating, the volunteers received an intravenous infusion that was either inert or contained a high or low dose of CCK. The scientists told them that their blood-hormone concentrations were being monitored and didn’t emphasize the importance of food intake to the study.
Before the study began, the elderly group, average age 71, ate roughly 30 percent less than the young people, whose average age was 23.
During the experiment, this gap widened. The older participants ate 16 percent and 48 percent less than their normal amount when receiving a low or high dose of the CCK, respectively. The young people ate 34 percent less than usual after high doses of CCK but consumed slightly more than normal when given low doses, the team reports in the December Journal of Clinical Endocrinology and Metabolism.
“This is a well-structured study,” says endocrinologist Margery C. Beinfeld of the Tufts University School of Medicine in Boston. Noting that regulation of appetite is complex, she adds, “CCK isn’t the only factor, but it’s an important one.”
CCK could explain in part why elderly people are so susceptible to anorexia, Morley says.
The older people entered the study with higher CCK concentrations in their blood than the young people did, a result that jibes with earlier studies.
Slowed metabolism in old age makes the body require less food, so even healthy seniors tend to eat lightly. But excess CCK may make some elderly patients and people with certain diseases less able to fend off illness, Beinfeld says.
Drugs to offset effects of CCK might restore appetite in some people suffering from severe weight loss, Morley says. Appetite stimulants already available counteract immune proteins called cytokines or use a chemical found in marijuana to boost desire for food. These drugs work in some cases, Morley says, but aren’t ideal. Drug companies are now testing numerous so-called CCK antagonists, he says.