Lipoic Acid Helps Restore Smell and Taste

Lipoic Acid’s Varied Benefits

Sensory impairments can have multiple causes, including age and diabetes
By Aaron W. Jensen, Ph.D.

“. . . smell and taste are in fact but a single sense, whose laboratory is the mouth and whose chimney is the nose."
— Jean Anthelme Brillat-Savarin (1755–1826), French lawyer, politician, and gourmet

Try to imagine life without your sense of taste—without the ability to appreciate the luscious flavors of a strawberry or a doughnut, a slice of bacon or a chocolate truffle. It’s a horrible thought, isn’t it? To be honest, though, taste is the least essential of our five senses, and it’s certainly the crudest, presenting us with less information about the world around us than any of the other four. It’s an oddity of nature that we are able to distinguish only five basic tastes: sweet, sour, salty, bitter, and umami (see the sidebar on that last one). Yet we all know that food offers an endless variety of rich and subtle flavors. How is it that only five different types of taste receptors have been identified, yet we are able to perceive and savor such an abundance of flavor?

Umami—The Fifth Taste

Gone are the days of only four basic tastes: sweet, sour, bitter, and salty. We now know that there is a fifth taste, a distinct but subtle one called umami (pronounced oo-mah´mee). It’s a Japanese word that the English language, which has no equivalent, has adopted. The word was coined one century ago by the Japanese scientist who discovered that umami is a distinct taste.

In a vague sense, umami means “deliciousness,” but that’s just the beginning. Scholars and gourmets, struggling to find a way to characterize umami, have suggested a variety of terms, such as pungent, essence, savory, and meaty. Try to imagine some combination of all of those—but in a subtle way, and having nothing of the other four tastes in the mix. It may be hard to classify or identify, but it’s real, and it’s been there all your life, contributing to the overall flavor sensation of many foods.

How do we know it’s real? Because scientists have discovered specific umami taste receptors that are different from the other four. The umami receptors respond to certain classes of organic compounds, notably glutamate, which is derived from glutamic acid, one of the amino acids found in food proteins. Meat contains a lot of glutamate, which may explain the “meaty” part of the definition of umami. Glutamate is also the principal constituent of the food additive monosodium glutamate (MSG), which is known to enhance the flavors of many foods. Thus we can think of MSG as adding a touch of umami—“deliciousness plus”—to our food.

Part of the explanation is that the different taste receptors in our mouth act in concert to give a more complex response than just a single sensation of, say, sour or salty. Our taste receptors are grouped into small packets called taste buds, each consisting of about 50–150 receptor cells. An adult has about 9000 taste buds; most are on the tongue, but some are on the palate and even in the throat. Our taste buds are not all the same, nor are all the receptor cells in a given taste bud of the same type. Some taste receptors respond to sugar molecules to yield a sweet sensation, while others produce a sour, salty, bitter, or umami sensation.

If only one kind of taste receptor is strongly activated, as is the case when biting into a lemon, e.g., then a single response (sour) is sent to the brain. A more complex signal, however, is produced when drinking sweetened lemonade, perhaps from a glass with a salted rim—then we recognize sweet, sour, and salty flavors all together. Depending on the relative strengths of each of these factors, we can get a spectrum of different taste sensations. But does that account for the great variety of flavors we’re able to perceive? Not by a country mile—there’s much more to “taste” than that.

You Can’t Have Good Taste Without Good Smell

Our sensation of taste depends critically on our ability to smell. In the roof of our nasal cavity is a small patch of odor-receptor cells—millions of them—which add enormous sensitivity and complexity to what we think of as our sense of taste. As we exhale, these receptors are bombarded by molecules of aromatic compounds that are released from foods and beverages in our mouth, so we’re literally smelling our food from within, more than actually tasting it. The combination of these two senses increases by orders of magnitude the different “taste” sensations that we experience. To prove this to yourself, hold your nose as you sample a particularly flavorful food: most of the flavor will disappear. Kids soon learn that trick—ever notice how they hold their noses as they grudgingly eat some vegetable they hate?

Children generally have acute but unsophisticated senses of taste and smell, which may explain why they’re often such finicky eaters. Sadly, however, many people suffer from some degree of loss of these very gratifying sensations (see the sidebar “Are You Eating As Well As You Should?”). For those who feel resigned to this dreary fate, snap out of it! There is good news: the common nutrient lipoic acid seems to help. Two research groups, one in Italy and England, and the other in Germany, have reported that lipoic acid independently improves dysfunction of both smell and taste.

Are You Eating As Well As You Should?

Current estimates suggest that up to 10 million people in the USA have an impaired or distorted ability to taste or smell. These problems occur primarily in the elderly, usually beginning between the ages of 60 and 70. They account in part for the poor eating habits of many older people, who don’t eat as much or as well as they should, because they simply don’t enjoy their food as much as they once did.

Poor nutrition tends to exacerbate existing medical conditions and may make a person more vulnerable to new ones, leading to a downward spiral in health that can be hard to reverse. It can contribute to wasting in chronic liver disease and cancer. It’s therefore important to maintain your senses of taste and smell, not just for the enjoyment of your food, but for staying healthy as well. It appears that supplementing with lipoic acid may be helpful in this regard.

Another tactic, of course, is to use flavoring agents to make food more palatable. Umami items, for example, can be used to encourage healthy eating. The umami receptors are stimulated by MSG (monosodium glutamate), but other flavoring agents called IMP and GMP can be used when low sodium is desired (ask at a health food store).

Although aging is the primary cause of impaired taste or smell, various medical conditions are also implicated, notably diabetes (for which lipoic acid is known to be helpful). Taste impairment, in fact, may be a good indicator of the course of diabetes, because it predicts the occurrence of other degenerative complications.1

Nasal and sinus disorders, such as allergic rhinitis, nasal polyps, and chronic sinusitis, account for smell dysfunction in many individuals; the degree of impairment corresponds to the severity of the disease. Another culprit—one that we have all encountered while sick with a cold or flu—is viral infection of the upper respiratory tract. In some cases, such infections cause a loss of smell that may persist for months or even years thereafter, probably owing to viral damage to the olfactory epithelium—the area of the nasal lining that contains the olfactory receptors.

Still other factors that may impair or distort the senses of taste or smell are head trauma (which can degrade the neural transmission of sensory inputs), zinc deficiency, exposure to toxic chemicals, lesions of the tongue, seizure disorders, depression, endocrine disorders, cardiovascular incidents, and various drugs.

  1. Kettaneh A, Fain O, Stirnemann J, Thomas M. Taste disorders [article in French]. Rev Med Interne 2002 Jul;23(7):622-31.

How Well Do You Smell?

To investigate the effect of lipoic acid on the sense of smell, the German researchers monitored a group of 23 individuals (median age 57; range 22–79) who had olfactory dysfunction following viral infection of the upper respiratory tract.1 Four of the patients suffered from complete loss of smell (anosmia), while 19 reported a reduced loss (hyposmia); the average duration of the loss was 14 months (range 4–33 months). All patients received the same treatment—600 mg/day of lipoic acid for an average of 4.5 months (range 3–11 months)—and all were subjected to a trio of standardized olfactory tests before and after the treatment period.

The tests employed were: odor threshold (establishing the lowest concentration at which a certain molecule, phenylethyl alcohol, could be detected); odor discrimination(identifying which of three odors was distinct from the other two, using a battery of 16 different odor combinations); and odor identification (identifying 16 different odors based on written descriptors). The results of these tests were combined into a single number—the “threshold, discrimination, and identification,” or TDI, score—which is used to evaluate the degree of olfactory dysfunction.

Lipoic Acid Improves Sense of Smell

Following treatment with lipoic acid, most of the patients showed significant improvement in their ability to detect and distinguish odors. Based on individual TDI scores, six patients (26%) exhibited “moderate improvement” over the study period, while eight patients (35%) showed “remarkable improvement.” Olfactory function remained unchanged in seven patients (30%), while two patients (9%) exhibited a further decline in function. Overall, the improvements were more pronounced in the younger individuals than in those over 60, and the younger they were, the more they benefited.

With lipoic acid, 26% of the 
patients exhibited “moderate 
improvement,” while 35% showed 
“remarkable improvement” in 
tests of olfactory function.

The authors caution that because this was an uncontrolled trial (no patients received placebo instead of lipoic acid), further studies are required to verify the results, especially given the fact that spontaneous recovery may occur in some individuals over time. Nonetheless, they believe that lipoic acid offers some patients a distinct advantage in recovering their sense of smell, claiming that “. . . the present results indicate that lipoic acid may be helpful in patients with post-URTI [upper respiratory tract infection] olfactory loss . . . .”

Lipoic Acid Improves Sense of Taste

A better way to run a clinical trial is to have it randomized and controlled, with one group of patients receiving the treatment and a similar group receiving placebo. Following this type of protocol, the Italian and British researchers investigated the effect of lipoic acid on idiopathic dysgeusia (taste impairment from an unknown cause) in 44 patients (median age 43; range 18–67).2 The treatment regimen here consisted of 200 mg of lipoic acid three times daily (600 mg/day total) for 60 days. At the end of the trial period, 46% of the lipoic acid group reported that they had completely regained their sense of taste, while 27% reported “decided improvement”; in all, 91% reported at least some improvement with lipoic acid.

In the control group, by contrast, there was no such success, although 36% did report “slight improvement.” When these patients were then switched from placebo to lipoic acid treatment for another 2 months of study, however, 36% reported “decided improvement,” while an additional 36% showed “slight improvement” (a remarkable coincidence of 36s here!). Thus there was a doubling of the number of patients who showed at least some improvement when they switched to lipoic acid.

It must be noted, though, that although this trial was controlled, it was not blinded, i.e., all the patients knew whether they were getting lipoic acid or placebo. That’s unfortunate, because the power of suggestion was thus surely a factor in determining the results. Further, more rigorous trials will be needed to get a truer picture of lipoic acid’s benefits in restoring the sense of taste.

Kiss Burning Mouth Syndrome Good-Bye

Lipoic acid also proves beneficial to individuals who suffer from a condition calledburning mouth syndrome (BMS)—a chronic burning or stinging sensation in the mouth that can be very painful.* The cause of BMS is largely a mystery, but some researchers believe that it may be a peripheral neuropathy (nerve damage in the extremities) of a kind similar to those that are often seen in advanced cases of diabetes (diabetic neuropathies). Since lipoic acid is known to be effective in treating neuronal (nerve-cell) damage, especially in diabetic neuropathy, it would make sense to investigate this nutrient for any possible benefit in treating the symptoms of BMS.

* See “Lipoic Acid Helps Quench the Fire of Burning Mouth Syndrome” in Life Enhancement, November 2002.

The same group of Italian and British researchers mentioned above conducted a randomized and controlled (and this time double-blind) clinical trial in which they evaluated 60 patients who received either lipoic acid (600 mg/day) or placebo for 2 months.3 The improvements were dramatic: 97% of the patients on lipoic acid showed some improvement, compared with only 40% of the control patients. In the lipoic acid group, 73% had “decided improvement,” whereas none of the controls reached that level. Clearly, lipoic acid is effective in reducing the symptoms of BMS, as it is in improving diabetic neuropathies.

Lipoic Acid Is Beneficial in Diabetes

Lipoic acid is a molecular do-gooder. Numerous studies have shown that it helps to promote normal neuronal function, apparently by stimulating the release of nerve growth factors and enhancing motor-nerve conduction, among other things. And because it is a potent antioxidant, it protects neurons from cellular damage caused by highly destructive molecules called free radicals. But it goes one step further and actually helps to repair the damage caused by free radicals. The combination of these effects may help to restore normal nerve function that is so important in facilitating our senses of taste and smell.

Lipoic acid can help stem the 
complications that result from 
oxidative damage; studies have 
demonstrated reductions in the 
symptoms of advanced diabetes.

Lipoic acid is approved for the treatment of diabetic neuropathy in Europe, where it has been used for this purpose for over 20 years. Indeed, a renowned researcher from the University of Southern California’s School of Pharmacy, Dr. Lester Packer, published a paper on the prevention of diabetes complications with lipoic acid.4 He noted that lipoic acid can help stem the complications that result from oxidative damage and that clinical and laboratory studies have demonstrated reductions in the symptoms of advanced diabetes, such as cataract formation, vascular damage, and peripheral neuropathy.

Keep Up the Good Taste

Whether you have diabetes or not (and if you don’t, you should do everything in your power to prevent it), you surely want to continue to enjoy the wonderful tastes and smells that provide so much pleasure in daily life. Lipoic acid may be of help in keeping your senses keen, and thus in making you a healthier, happier person. Let’s go eat!

References

  1. Hummel T, Heilmann S, Hüttenbriuk K-B. Lipoic acid in the treatment of smell dysfunction following viral infection of the upper respiratory tract. Laryngoscope2002;112:2076-80.
  2. Femiano F, Scully C, Gombos F. Idiopathic dysgeusia; an open trial of alpha lipoic acid (ALA) therapy. Int J Oral Maxillofac Surg 2002;31:625-8.
  3. Femiano F, Scully C. Burning mouth syndrome (BMS): double-blind controlled study of alpha-lipoic acid (thioctic acid) therapy. J Oral Pathol Med 2002;31:267-9.
  4. Packer L, Kraemer K, Rimbach G. Molecular aspects of lipoic acid in the prevention of diabetes complications. Nutrition 2001;17(10):888-95.

Dr. Jensen is a cell biologist who has conducted research in England, Germany, and the United States. He has taught college courses in biology and nutrition and has written extensively on medical and scientific topics.