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Lipoic Acid’s Varied Benefits
Lipoic Acid Helps
Restore Smell and Taste
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
 ry 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?
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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.
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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.
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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.
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. -
Kettaneh A, Fain O, Stirnemann J, Thomas M. Taste disorders
[article in French]. Rev Med Interne 2002 Jul;23(7):622-31.
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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. 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). 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 called burning 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.
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. 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. 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
- Hummel T, Heilmann S, Hüttenbriuk K-B. Lipoic acid in the treatment of
smell dysfunction following viral infection of the upper respiratory tract.
Laryngoscope 2002;112:2076-80.
- 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.
- 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.
- Packer L, Kraemer K, Rimbach G. Molecular aspects of lipoic acid in the
prevention of diabetes complications. Nutrition 2001;17(10):888-95.
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