Zinc plays a central role in the olfactory system. Can it be used to alleviate symptoms of anosmia?
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In our previous article, we discussed loss of smell and taste, or Anosmia, one of COVID-19’s now well known symptoms. In our efforts to further explore the theories behind loss of smell and methods of alleviation, we did our research on the potential role of zinc in alleviating anosmia. Zinc is a mineral that has a function in the perception sites of the olfactory sensations. Oral zinc has been used to treat smell and taste disorders (STDs) that are caused mainly by some physiological changes or injuries. Such physiological changes are those that occur post traumatic anosmia, due to renal or liver failures or even due to pregnancy. 

Anosmia

Some of us have encountered loss of smell and taste before. In medical terminology, this loss of smell is called ‘anosmia’, while the term ‘ageusia’ is used for the condition when a person is unable to perceive tastes such as sweetness, saltiness and bitterness. Those two symptoms are collectively called Smell and/or Taste Disorders (STDs). 

As mentioned in our previous article, there are various causes of anosmia, for example, nerves injury due to surgical or head trauma; nasal polyps; post-viral anosmia or nasal congestion (most common) caused by flu, allergy, or sinus infections, etc.

These days, COVID-19 pandemic is prevalent in the world. Research studies have demonstrated that corona virus also causes acute symptoms of anosmia with a subsequent loss of taste which creates early clinical suspicion of this disease.

Zinc’s Potential Role in Alleviating Symptoms of Anosmia

In the past few months, a number of theories have been speculating that zinc could play a role in alleviating such symptoms of the corona virus.

Let’s find out if this is true or if it is just a myth. But before moving on to that, it is important to understand the anatomical and biological mechanism of how zinc is associated with the senses of smell and taste.

How Is Zinc Associated with Smell and Taste?  

Additionally, there is a zinc-containing enzyme in the taste buds. Carbonic anhydrase (CA) VI or gustin is essential for the taste buds to get stimulated.

Smell Receptors 

Our body has a very sophisticated mechanism for the perception of taste and smell. For both sensations, nature has provided us with special receptor cells. In the nose, we have olfactory hair cells present in the olfactory epithelium of the nasal roof. They act as receptors for the different kind of odorants. 

Taste Receptors 

In the case of taste, taste buds are residing on the tongue. They also have similar roles. Each receptor cell detects a particular kind of stimulus, and sends signals to the brain through nerves in the form of nerve impulses. Ultimately, the brain interprets these signals as sensations.

Role of Zinc in Smell and Taste 

Important thing to note is that just like epithelial cells on any other part of the body, these receptors and their supporting cells also are destined to death either naturally or due to some kind of injury. This daily cell loss can lead to ultimate loss of smell and taste perception.

However, there are stem cells present nearby which have the ability to divide and replace these dead ones. Thus, division of these stem cells maintains the normal cell count. At this point, zinc comes into action.

Zinc is an integral component of more than 300 enzymes of our body. Some of these zinc-containing enzymes are essential for stimulating the basal stem cells division. Moreover, some studies have also shown that normal levels of zinc are important for peripheral nerve conduction from sensory receptors to the brain.

Additionally, there is an enzyme carbonic anhydrase (CA) VI, also known as gustin, which is present in the taste buds. It contains zinc, and is essential for the taste buds to get stimulated. Research study on mice also shows that deficiency of this zinc-containing CA VI causes abnormal perception of bitter tastes. 

Does Zinc Supplementation Improve Your Smell and Taste Sensations? 

It Was Found that Although Zinc Supplementation Does Not Have an Effect on Chemotherapy-Related Smell and Taste Changes, It Improved These Sensations in Patients with Zinc Deficiency.

Zinc is very essential in our diet, and it is the second most abundant trace element in our body after iron.

It functions at multiple sites in the perception of gustatory and olfactory sensations. Its correlation with the sense of smell has also been proved by various research studies. 

Correlation Between Zinc and Sense of Smell in Research

In a study, it was found that although zinc supplementation did not have an effect on chemotherapy related smell and taste changes, it improved these sensations in patients with zinc deficiency.

Similarly, in another research, zinc supplementations were given to 32 patients with alcoholic cirrhosis to check the results of this therapy. Alcoholic cirrhosis is an advanced liver disease caused by prolonged alcohol consumption. It causes the liver to become stiff and almost dysfunctional. Along with beneficial effects on cirrhosis, significant improvement in smell and taste sensations for a few patients was reported.

How Does The Corona Virus Cause Anosmia?

The Virus Replicates Inside Cells of The Olfactory Epithelium and Causes Cellular Injury. Death and Associated Inflammation of These Cells and Neurons Might Cause  Loss of Smell Sensation.

Corona virus also causes anosmia. A Research study shows that this virus enters the basal stem cells and sustentacular cells (structural support cells that have an involvement in odorant transformation) of the olfactory epithelium through Angiotensin Converting Enzyme-2 (ACE-2) receptors. Inside these cells, virus replicates and causes cellular injury. These cells support the receptors and neurons of the olfactory epithelium. Therefore, their cell death and associated inflammation causes the loss of sensations of smell.

Can Zinc Help You To Restore Your Sense of Smell Post  COVID-19 Infection?

Zinc Could Help to Combat Against Symptoms of the Corona Virus. Further Research is Needed to Confirm This Theory. 

Although no credible study is there showing how zinc cures these corona virus symptoms, it proves beneficial in shorting the duration of anosmia-like symptoms of COVID-19, and doctors recommend to take zinc supplements along with other vitamins.

The possible explanation of this role is that zinc strengthens the immune system of the body, and inhibits viral genome replication. Moreover, as explained earlier, zinc-containing metalloenzymes (enzymes containing metal ions) promotes cell division in basal stem cells, thus replacing the dead cells. In this manner, zinc may help to combat against corona virus symptoms.

Roles of Other Minerals and Nutrients in Alleviating Symptoms of Anosmia

Along with zinc, there are other nutrients and vitamins as well which are effective in the treatment of anosmia.

Vitamin A, C and D

Vitamin A has a comparable role to Zinc in the mechanism in olfaction. There are evidences which show that intake of vitamin A, which is abundant in cod liver oil, carrots and fruits, alleviates uncomplicated anosmia and post-infectious olfactory loss.

Similarly, other vitamins like vitamin C and D also seem effective in this regard.

Alpha-Lipoic Acid 

Alpha-lipoic acid, present in red meat, and vegetables like spinach, broccoli, etc, also reduces the symptoms of loss of smell.

It does so as it triggers the release of certain nerve growth-factors in the body that have a role in regulating the nerve cells and their conductive function. Therefore, signals are better conducted from the olfactory receptors to the brain. Moreover, this alpha-lipoic acid has anti-oxidant effects as well which protects the body cells from oxidative damages.

Omeg 3 Fatty Acids 

Another important nutrient is being recommended by the doctors is omega 3. It can be obtained easily by eating nuts, seeds, and seafoods like fish and salmon. Omega 3 is also neuro-protective just like lipoic acid. Moreover, it has anti-inflammatory properties in both peripheral and central nervous system.

Therefore, omega 3 supplementations are also given to the patients with anosmia-like symptoms.

All these nutrients and vitamins might help in reducing the duration of corona associated anosmia as they have a role in the sense of smell mechanism.

Patients are advised to eat healthy fruits, vegetables, walnuts, seafood, etc, just because of the above-mentioned nutritional benefits.

Zinc Has A Direct Role in The Biological Mechanisms of Anosmia

What I Should Eat to Get Enough Zinc in My Diet? 

Although various nutrients and vitamins are beneficial to treat loss of smell perception, zinc is the most important one because it has a direct role in the biological mechanism of anosmia. It comes into action at multiple steps of smell perception, like receptor stimulation (gustin), regulation of peripheral nervous conduction, basal stem cells division to replace the dead cells, etc.

Food Items Rich in Zinc 

There are many foods which are rich sources of zinc. These include oysters, red meat, beans, nuts, whole grains, cereals, dairy products, and seafood like lobsters and crabs. 

It is Recommended To Consume Zinc That is Animal-Based 

However, plant-based foods contain phytates in them. Phytates are naturally found in all plant-based foods. They bind with zinc and reduce its absorption from the gut. Therefore, animal foods have greater bioavailability for zinc in it when compared to plant sources despite of their rich levels of zinc.

What is The Recommended Daily Allowance of Zinc 

Excessive Consumption of Zinc Can Cause Zinc Toxicity. Therefore, Care Should Be Taken When Deciding to Take Zinc Supplements. 

However, excess amounts of zinc could be just as harmful as its deficiency. Therefore, we should take appropriate balanced diet to maintain normal zinc levels in the body.

According to the Food and Nutrition Board (FNB) at the institute of medicine of National Academies, the Recommended Dietary Allowances (RDA) for zinc is 11mg and 8mg per day for an average adult man and woman, respectively.

It is very important to reach up to this level, especially in these days of corona pandemic, because of the beneficial role of zinc in your immunity and in alleviation of anosmia.

However, oysters, nuts, whole grains, etc, and supplements should not be taken in excess in order to avoid zinc toxicity. Otherwise, it will cause more harm than good.

It Might Be Counterintuitive, But Did You Know that Zinc Sulphates Are Used to Induce Artificial Anosmia in The Lab 

Zinc sulphate is used to induce artificial anosmia in laboratory animals.

The anatomical basis behind this is that direct application of zinc sulphate in the form of intranasal spray causes apoptosis and severe rapid degeneration of the olfactory epithelium. This results in temporary loss of smell.

The evidence of this mechanism is that after stopping the introduction of zinc sulphate, sensations of smell returns to normal due to new cell production. 

What is The Take Away Message?

To put the above discussion in a nutshell, we can say that zinc has an integral role in the perception of taste and smell. Its adequate intake might help to alleviate anosmia and ageusia but further research is needed to confirm this hypothesis.

One should follow the daily recommended intake levels to get the maximum health benefits of zinc. 

Although other nutrients and vitamins also have similar advantageous effects, zinc is can be more effective due to its central role at multiple steps of olfaction.

However, more research studies need to be conducted to better understand the effectiveness of zinc in treating corona related anosmia.