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Taste and Smell Loss: Risk for Disease?

By Sophia Glezos

On the Front Page...
A reduced, distorted, or lost sense of taste or smell signifies much more than a weakened zest for food -- one of humankind's greatest sources of pleasure and comfort. These deficits represent serious risk factors for heart disease, diabetes, stroke, and other illnesses that require adherence to specific dietary regimens. Changes in these senses can also lower immunity to disease, contribute to digestive disorders, cause food poisoning, or produce toxic effects of environmentally hazardous chemicals that are otherwise detectable.

Continued...
The ways in which eating-related behaviors and these sensory losses may harmfully interact with disease, or favorably influence wellness, was the topic of a recent seminar in a monthly series that the NIH Office of Behavioral and Social Sciences Research supports on behavioral and social factors in health issues.

Guest speaker Dr. Susan S. Schiffman, a Duke University researcher and NIH grantee, said the most common groups of people affected by these sensory insufficiencies are those 60 and older; individuals of any age who suffer from certain illnesses or medical conditions; and patients who take particular types of medication or who undergo radiation therapy.

In the United States, approximately 2 million adults have disorders of taste and smell. Although it is not known how many elderly people have these dysfunctions compared to those in other vulnerable groups, a large proportion is believed to have one or both deficits.

"Gradual reduction, or loss, of taste and smell appears to be an unfortunate but normal part of aging," Schiffman said, "but it also accompanies illnesses or conditions such as multiple sclerosis, Bell's palsy, head injury, diabetes, liver and kidney diseases, hypertension, and zinc or niacin [vitamin B3] deficiency." Other correlates of these sensory deficits she noted were Alzheimer's disease, tobacco smoking, surgical interventions, certain dental conditions such as infected teeth and gums, and cerebral tumors. "These disorders," Schiffman said, "modify food choices and dietary habits -- either favorably or not -- but most of them exacerbate diseases or nutritional deficiencies."

An example of the medical impact that a reduced sense of taste or smell may impose is seen in people with hypertension, or high blood pressure -- a condition that if left untreated may lead to stroke, heart disease, or other medical problems. Since research evidence shows a clear causal link between sodium intake and high blood pressure, physicians advise hypertensive patients to reduce salt in their diets. Yet, patients who develop disease-induced taste deficiency typically add more salt to meals, simply because the foods are, to them, tasteless. But, the more salt added, the greater the chance of stroke or other disabling health consequences.

Taste sensitivity is also reduced in people who have diabetes, an illness marked by unstable blood-sugar levels that, if not controlled, can lead to serious medical disorders. In diabetes, ingestion of certain types of carbohydrates contributes to dangerously high blood-sugar levels. Thus, taste reduction becomes a serious health risk when diabetic patients compensate for a reduced sweet taste by adding more sugar to already sweetened foods or beverages.

In the elderly, Schiffman pointed out, taste and smell, typically, are not completely gone, but thresholds for these senses are higher. In a study published in the New England Journal of Medicine, she examined taste thresholds for sweeteners, sodium salts, acids, and bitter compounds in healthy elderly individuals and younger counterparts. Results showed the threshold in each taste category was higher in the older study subjects. For sweet taste, the threshold was 3 times as high, salt detection was 11 times greater, acid detection was more than 4 times elevated, and bitter tastes were almost 7 times higher.

While these sensory dysfunctions reduce the enjoyment of life for affected individuals -- and increase the risk of developing depression and unwanted weight loss -- the good news is that in many cases they are temporary or minor. Also, these disorders are often reversed when underlying medical conditions are effectively treated or offending chemicals or medications are eliminated.

Although several remedies appear moderately useful in treating the more intractable cases of taste and smell disorders, persuasive evidence for their efficacy is limited. However, treatments showing some promise include vitamins A and B3 supplementation, which may restore taste if these nutrients are deficient, and zinc sulfate use even though a deficiency of the mineral may not exist.

Self-help techniques for enhancing flavor are to chew well and to alternate bites of different foods in one meal. Chewing breaks down food and allows more molecules to interact with taste and smell receptors, and switching from one food to another helps counteract the phenomenon of sensory adaptation. Also, the use of monosodium glutamate (MSG) in foods, and other flavor enhancers, has diminished the problem for some people. But MSG must be mixed with 5'-ribonucleotides when adding to foods, Schiffman warned, both to further intensify its enhancing effect and to reduce its otherwise high sodium content, which far exceeds that of table salt. (The chemical 5'-ribonucleotides is available through nutritionists or some food distributors.)

"When healthfully and appropriately used, flavor enhancers can make a huge difference in taste," Schiffman said.

For treating olfactory dysfunction, somewhat effective approaches include the use of certain steroids; acetate; vitamins A, B complex and E; antibiotics; and the more drastic measure of intranasal cryosurgery.

"For many people with taste or smell dysfunctions, life has lost its gusto," Schiffman said, both in the figurative and literal senses, "but food enhancers and other treatment approaches, when used properly and with a physician's guidance, can help 'nontasters' comply with dietary restrictions and at the same time enjoy food again."

Upcoming OBSSR seminars, each of which will be held from 10 to 11 a.m., will feature Dr. John B. McKinlay, New England Research Institute, "Psychosocial and Behavioral Influences on Clinical Diagnostic Decisions," Apr. 28; and Dr. Lisa F. Berkman, Harvard School of Public Health, "Social Relationships, Connectedness and Health: The Bonds That Heal," May 29, both in Bldg. 1's Wilson Hall; also, Dr. Alan M. Kraut, American University, "Silent Travelers: Germs, Genes, and the Immigrant Menace," June 27, in the Natcher Bldg.