Taste and Smell Problems

Sense-sational Nutrition

Imagine being unable to smell a bank of honeysuckle blooming along a country road or to savor the sweetness of a freshly picked raspberry. Most of us would feel seriously deprived if we were denied these simple pleasures.

Unfortunately, that's what happens to people with taste and smell problems. (The two senses are so closely linked that people who can't smell often complain that they can't taste anything, either.)

For some people, these two vital senses may tend to decrease with age, for no apparent reason. For others, taste and smell drop off quickly, the result of a viral infection, a head injury or cancer therapy or as a side effect of certain prescription drugs.

People may also develop disturbing sensory changes, such as a metallic, bitter or salty taste that can occur by itself or be triggered by foods (citrus is a common culprit). In some cases, senses recover after a time, although they may never be as sharp as they once were.

Although most physicians are unfamiliar with these problems, it's still best to seek medical attention if something seems to be wrong with your sense of taste or smell. See your family doctor or an ear, nose and throat specialist, or call the nearest university hospital to find out if there's a taste and smell clinic nearby. Such centers draw on a variety of specialists to troubleshoot your problem.

While there are any number of treatments that your doctor may consider, you should be aware that one nutrient has definitely been linked to taste and smell disorders: zinc, an essential mineral, according to researcher Robert Henkin, M.D., Ph.D., director of the Taste and Smell Clinic of the Center for Molecular Nutrition and Sensory Disorders in Washington, D.C. Here's the latest thinking--and controversy--on this connection.

Zinc May Account for Good Taste

There's no doubt that people with severe zinc deficiencies, which are rare in the United States, often lose their sense of taste. But there's one thing that many of the doctors who treat taste and smell disorders apparently do not know (or believe, for some reason): Even a relatively mild zinc deficiency can cause problems, says leading zinc researcher Ananda Prasad, M.D., Ph.D., professor of medicine at Wayne State University School of Medicine in Detroit.

"Years ago in Iran, we found aberrations in taste in young boys who were zinc-deficient. Their growth and sexual maturity were retarded, and they ate clay," he explains. "More recently, we found that volunteers made mildly zinc-deficient also lost some of their taste acuity." (Eating clay is a strange deficiency symptom known as geophagia.)

The volunteers, all healthy young men, weren't being seriously deprived of zinc, Dr. Prasad says. They ate what might be considered a fairly typical vegetarian diet, getting about five milligrams of zinc a day, one-third of the Daily Value. And they ate soy as their main source of protein. "Soy and grains contain phytates, compounds that interfere with the absorption of a variety of nutrients, including zinc," Dr. Prasad explains. The volunteers' sense of taste diminished after six months on the diet. (They also developed problems adapting their eyes to darkness.)

When these people were supplemented with 30 milligrams of zinc a day, their ability to taste returned in about two to three months.

Both taste buds and olfactory (smell) cells, which are found high in the nose, are specialized cells. They depend on zinc, along with other nutrients, for their growth and maintenance, Dr. Prasad explains.

Taste buds are especially dependent on zinc, says Dr. Henkin. He found that cells in the salivary glands make gustin, a zinc-dependent protein that is secreted in saliva. "Gustin is important in maintaining the sensation of taste," Dr. Henkin says. "It acts on the stem cells that are in the taste buds, causing these cells to differentiate, or to divide and develop into new taste bud cells."

Dr. Henkin believes that about 20 to 25 percent of taste and smell problems are zinc-related, not necessarily because people are zinc-deficient but because their bodies are unable to use zinc properly. "About half of these people benefit from additional zinc, but others don't improve no matter how much zinc they get," he says. He believes that these people have problems making gustin.

If you believe that your taste or smell problem may be linked to low zinc intake, discuss it with your doctor. And if your doctor recommends blood tests, keep in mind that the most commonly done tests, blood plasma and serum zinc levels, detect only severe deficiency, not mild to moderate deficiency, Dr. Prasad says. He measures the zinc content of lymphocytes (white blood cells), a much more sensitive test performed in only a few laboratories nationwide. Dr. Henkin, on the other hand, uses a measurement of zinc in saliva, which reflects the activity of the zinc-dependent enzyme that stimulates taste bud cells to grow and develop. This test, however, is not readily available.

Dr. Prasad believes most people can safely get up to 30 milligrams of zinc a day from foods and supplements. "More than that amount of zinc may interfere with copper absorption and so requires supplementation of 1 to 2 milligrams of copper daily, along with regular blood tests to check for anemia," he cautions. In addition, it's best to consult your doctor before taking zinc in doses of more than 15 milligrams daily, since large amounts of the mineral can be toxic.

Seafood and meats provide the most easily absorbed form of zinc. Eastern oysters are far and away the best source, with six cooked medium-size oysters providing about 76 milligrams of zinc. Three ounces of beef, veal, lamb, crab or pork provides about 7 milligrams of zinc. If you're taking supplements, zinc acetate and zinc gluconate deliver the goods with less stomach upset than zinc sulfate, Dr. Prasad says.

If zinc is going to improve your taste, it should begin to do so within three months, Dr. Prasad says. If you don't notice an improvement by then, it's likely that zinc is not going to help you. You should then cut back to the Daily Value, 15 milligrams, and consider some other cause of your problem, he advises.

Zinc-related sensory abnormalities, including decreased taste and smell acuity and problems adjusting your eyes in the dark, have been associated with a number of conditions, Dr. Prasad reports: liver disease, kidney disease, Crohn's disease, cystic fibrosis, Parkinson's disease, thyroid problems, multiple sclerosis, serious burns, Type II (non-insulin-dependent) diabetes, flulike infections, sickle-cell anemia and anorexia. These abnormalities have also been noted in people taking penicillamine, a rheumatoid arthritis drug. Dr. Prasad also believes that vegetarians and older people who don't eat much food, including meats, are often shortchanged on zinc. "Mild deficiency is much more common than most people realize," he says.