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DURHAM, N.C. -- Elderly people often lose so much of their ability to taste and smell that they could risk serious health consequences as a result of poor nutrition and the loss of sensory pleasure from food, according to a review article in the Journal of the American Medical Association (JAMA).

Duke psychologist Susan Schiffman, author of the Oct. 22 article that reviewed 30 years of scientific literature on the subject, said the decline in taste and smell can be severe enough to put elderly people at risk for malnutrition, lowered immunity to disease, accidental poisonings, and chronic diseases like hypertension and diabetes.

The problem is common: more than three-fourths of people over 80 have major difficulty identifying and perceiving odor, Schiffman said, and the losses can be dramatic. Compared to younger people, elderly people taking an average of three medications required two to 15 times more of an odor or taste before they could detect it.

Although some sensory loss is normal with age, Schiffman said taste loss in particular is considerably worsened by certain medications, surgical procedures and disease processes.

"Deficits in taste and smell not only reduce pleasure and comfort from food, but they can alter the types and amounts of food eaten and can actually reduce the levels of key immune system cells, like T-cells and B-cells," Schiffman said.

While taste and smell have long been known to regulate mood and well-being, Schiffman's own research published in more than a dozen peer-reviewed journals over the years was among the first to prove that taste and smell have a direct link to mental and physical health, not just a related effect through pathways that regulate mood.

The dangers of "chemosensory" deprivation are numerous, Schiffman said. Deficits in sweet taste perception make elderly people with diabetes more vulnerable to the adverse effects of excess sugar, while loss of salt perception can cause hypertensive patients to inadvertently eat too much salt. Loss of salt perception is the biggest taste deficit for elderly people taking medications; compared to younger people, they required as much as 12 times the amount of salt in order to taste it, making older people at greater risk for stroke and high blood pressure.

Even in healthy people, sensory loss can be troublesome. Such difficulties can lead to food poisoning or exposure to hazardous chemicals that would normally be detected by taste and smell.

Without taste and smell, elderly people are unable to select appropriate foods and portion sizes, and they eventually lose the primary reinforcement to eat -- the pleasure derived from tasting and smelling food, Schiffman said. That pleasure takes on particular importance in elderly people for whom other sources of gratification, such as work, family and hobbies, may be limited.

"The loss of pleasure in food can result in malnutrition, especially among people in nursing homes who no longer have control over their food choices and are eating new and unfamiliar foods," Schiffman said. "Malnutrition, in turn, can cause further chemosensory losses by impairing the reproduction of taste cells in the taste buds."

Taste buds are oval-shaped structures on the tongue and palate that consist of up to 100 specialized cells arranged somewhat like segments of an orange. Taste cells constantly reproduce themselves, with a lifespan of approximately 10 days, a renewal process that can be hampered by malnutrition.

Finally, taste and smell are important because they prepare the body to digest food by triggering secretions from the pancreas, intestines, stomach and salivary glands.

While few, if any, treatments exist to restore taste and smell, Schiffman has found that enhancing foods with flavored powders can significantly increase the flavor and enjoyment of the meal. Moreover, her study of patients who ate foods enhanced with powdered flavors like beef, bacon and cheese showed they had significantly higher levels of B-cells and T-cells than when they ate the same foods without enhancers. While the patients ate more of the flavor enhanced foods, nutrition alone did not account for the increased immune status.