COVID-19, sense of smell, and zinc

If you lose your sense of smell all of a sudden, it is most likely a sign that you have been infected with the coronavirus, according two large, international studies published in the science journal Chemical Senses. Many COVID-19 patients also lose their sense of taste and even if there are no other complications, it can affect their quality of life. The big question is if there is a link between zinc deficiency, corona infection, and these symptoms. It is already an established fact that zinc is important for our immune defense, for our sense of taste and smell, and as an antioxidant that protects our cells. Also, it is known that zinc deficiencies are rather common and people with unhealthy eating habits, vegetarians, vegans, older people, and diabetics are at increased risk. Birth control pills and certain types of medicine also increase the risk of lacking zinc.

There can be different reasons why you lose your sense of smell, but it has been known for some time that the loss of this sense often follows in the wake of a COVID-19 infection. Two large, international studies published in Chemical Senses confirm that there is a very big chance that the sudden loss of your sense of smell can be caused by a coronavirus infection. According to associate professor Dr. Alexander Wieck Fjældstad, from the Department of Clinical Medicine at Aarhus University, who headed the Danish arm of the study, you should think of yourself as being infected until proven otherwise. In other words, if you have lost your sense of smell and are unable to get a COVID-19 test immediately to find out if you have COVID-19, you should isolate.
As it turns out, a lot of people infected with COVID-19 do not just suffer a mildly reduced sense of smell but lose it, altogether. In most cases, their sense of smell returns after around 40 days or so. Furthermore, many COVID-19 patients lose their sense of taste and their sense of touch in the mouth. This destroys their ability to enjoy food and life in general. Also, they risk eating food that has spoiled because they are unable to taste or smell it.
It is commonly known that COVID-19 infections cause people to cough and have breathing difficulty. Still, many corona patients just experience taste and smell disturbances. It is therefore important for these people to get tested so they do not pass on the infection to others.

Why does COVID-19 affect your sense of smell and taste?

Our olfactory system (sense of smell) that features around 40 million olfactory cells is located in the upper part of the nasal cavity. The mucous traps fragrances that are registered by the olfactory cells. From here, information is passed on to the brain. That is why our sense of smell, mood, and memory are closely connected. Olfactory cells have a lifespan of around 6-8 weeks. When the die, they are replaced by new cells. Therefore, our sense of smell is restored if our mucosae are damaged.
It is rather common to lose your sense of smell if you have an upper respiratory infection, including colds and flus that are caused by different types of coronavirus. For that reason, it is believed that the link between a COVID-19 infection and losing your sense of smell or taste is rooted in the mucosae, not in the brain. Previous studies have shown that COVID-19 gains access to the host cells by binding to ACE2 receptors. ACE2 (angiotensin-converting enzyme) is found in the membranes of cells in e.g. the respiratory system.
A COVID-19 infection generally begins with virus infecting cells in the nose by way of the ACE2 receptors. A well-functioning immune system is able to destroy the virus before it can replicate and spread. However, it the immune system does not function optimally, COVID-19 replicates in the nasal cells and spreads to surrounding cells through the ACE2 receptors in the airways, arteries, heart, small intestine, and kidneys.
The presence of virus in the respiratory tract can therefore make you lose your sense of smell and taste. Also, sensory cells may be damaged by exaggerated immune reactions, including inflammation.

Zinc’s role in the immune defense and the sensory system

All cells in the body depend on zinc, a nutrient that is involved in well over 300 different enzyme processes. Zinc is important for our sense of taste and smell and it is commonly known that lack of zinc can impair these senses. Zinc also helps stabilize cell membranes against virus attacks. As soon as you can an infection, the zinc levels in your blood drop because both your innate and adaptive immune defense use the nutrient to carry out swift and targeted attacks.
The immune defense also mobilizes cascades of free radicals as part of these attacks. It is vital to prevent these free radicals from causing oxidative stress, which is an imbalance between harmful free radicals and protective antioxidants. Zinc is a constituent of a powerful antioxidant called SOD (superoxide dismutase) that counteracts cell damage caused by free radicals and oxidative stress.
Zinc-containing proteins also code for around 10 percent of our genes and that is essential in order to enable the cells in the immune defense and other tissues to carry out their tasks correctly.
A zinc deficiency therefore results in weak cell membranes and a malfunctioning immune defense that makes us more susceptible to infection, unwanted inflammation, and local damage to cells and tissue.
Earlier studies have shown that zinc deficiency is quite widespread among COVID-19 patients and that increases the risk of spreading the infection. Although more research is needed, it is possible that having too little zinc can increase the risk of losing your sense of smell and taste in connection with COVID-19 because the cells become more vulnerable to virus attacks and because the immune defense consumes large amounts of zinc, thereby leaving too little zinc for other functions that depend on the nutrient.

Zinc supplements are useful against infections with different types of coronavirus

Cold infections are often caused by different types of coronavirus. A Finnish meta-analysis has shown that taking large doses of zinc for a short period of time can shorten the duration of a cold. Several studies suggest that it is best if you start taking zinc supplements soon after contracting an acute respiratory infection. This may also be the case with COVID-19.

Why are zinc deficiencies so common?

There is a lot of zinc in oysters and shellfish, fish, dairy products, nuts, kernels, and beans. Animal sources of zinc have better absorption in the body. Although clinical zinc deficiency is rather rare in our part of the world, subclinical zinc deficiency is widespread and can easily affect your health.
Lack of zinc and poor utilization of the nutrient may be a result of poor eating habits, lack of animal protein, high calcium intake, excessive consumption of alcohol, ageing, celiac disease (gluten intolerance), diarrhea, diabetes, and kidney diseases. The same goes for several kinds of medicine such as diuretics, ACE inhibitors, antacids, corticosteroids, antibiotics, and birth control pills.

Official recommendations and safe upper intake level

• The reference intake (RI) level (in Denmark) is 10 mg
• The European Food Safety Authority (EFSA) has established a safe upper intake level of 25 mg/day for adults and pregnant women
• It is safe to ingest even larger doses from e.g. oysters or supplements for a brief period

Zinc supplements are easier for the body to utilize

It is vital to get enough zinc from dietary sources and to make sure that the zinc you get is absorbed properly. With regard to supplements, pay attention to the fact that many zinc preparations contain inorganic zinc sources like zinc sulphate and zinc oxide, which the body cannot absorb all that well. Look carefully at the label to see what is in the tablets. Zinc gluconate and zinc acetate are both organic zinc sources that the body can easily absorb and utilize.

References

Anne Sophie Thingsted. Mistet lugtesans er det sikreste symptom på COVID-19. Videnskab.dk 19. januar 2021

Ozlem Equils et al. Proposed mechanism for anosmia during COVID-19: The role of local zinc distribution. Oat. 2020

Nikki Hancocks. Diet and supplements: Swiss panel publishes COVID-19 recommendations. 2020

Luke Maxfield, Jonathan S. Crane. Zinc Deficiency. NCBI March 18, 2019

University of Helsinki. Zink acetate lozenges may increase the recovery rate from the common cold by three-fold. ScienceDaily May 11, 2017

Zink for Colds, Rashes and the Immune system. WebMD. 2017

Frida - Parametre (fooddata.dk)

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