Zinc, Thymus Function & Immunity
Written by Michael T. Murray, ND
Reprinted from Vitamin Retailer Magazine

The importance of the health of our immune system has become painfully obvious with the COVID-19 pandemic. It has led consumers to seek out natural products to boost immune function. And there are clearly some key dietary supplements that offer important immune enhancing effects. There is a key fact that has to be communicated to the public.

Our immune system is just that--it is a system that relies on a complex interplay of many different factors. A deficiency of any single nutrient can disrupt the entire system. For example, zinc functions in close companionship with vitamin A and vitamin D, selenium and many other nutrients. A deficiency of any of these other nutrients will undermine the benefits of zinc. That said, deficiency of the essential trace mineral zinc offers a clear picture of just how important a single nutrient can be to immune function.

The critical role that zinc plays in immune health is simply incredible. As it relates to viral infections, without adequate zinc levels in our body, the immune system can't mount an effective counterattack against viruses and other disease-causing organisms.

How Common Are Low Zinc Levels?
Low zinc levels are very common, especially in children and the elderly. It is estimated from national health surveys that as high as 67 percent of the adult population do not consume the recommended dietary intake (RDI) for zinc. Insufficient intake of zinc can lead to a number of signs and symptoms including increased risk for infection, delayed wound healing, skin disorders, poor night vision, bad breath and a decreased sense of taste or smell. (NOTE: the loss of taste and smell associated with COVID-19 infection may be the result of depleted zinc stores.) If you are a vegan or have kidney disorders or chronic diarrhea, your body zinc levels are likely to be low. Other conditions associated with zinc deficiency are listed below.

Conditions Predisposed to Zinc Deficiency Decreased intake:

• Acute infections/inflammation
• Alcoholic cirrhosis
• Alcoholism
• Anorexia nervosa
• Burns
• Post-trauma
• Protein deficiency
• Vegetarian diet
• Starvation

Decreased Absorption:
• Alcoholism
• Celiac disease
• Chronic blood loss
• Diabetes mellitus
• Diarrhea
• High fiber diet
• High dietary calcium:zinc ratio
• High dietary iron:zinc ratio
• Inflammatory bowel disease
• Intestinal resection
• Liver disease
• Pancreatic insufficiency
Increased Requirement:

• Old age
• Pregnancy and lactation
• Oral contraceptive use
• Growth spurts and puberty

Role of Zinc in Immune Function
There is a big reason why when people look to boosting the immune system that zinc is among the top of list, especially when bolstering against viral infections. Zinc serves a vital role in many immune system reactions. It is involved in virtually every aspect of immunity, but its most important effects are on thymus function and hormones, white blood cell function and signaling, and in our "innate immunity."

Zinc and the Thymus Gland
One of the main ways that zinc promotes a healthy immune system is through its role in thymus function. The thymus is the major gland of our immune system. It is composed of two soft pinkish-gray lobes lying in a bib-like fashion just below the thyroid gland and above the heart. To a very large extent, the health of the thymus determines the health of the immune system. Zinc is critical to thymus health and function.

The thymus gland is the master control of what is known as cell-mediated immunity, an immune response that does not involve antibodies. Antibodies are proteins that certain white blood cells produce that are designed to bind to and help destroy invaders. Cell-mediated immunity is different. It involves the activation of white blood cells known at T-lymphocytes or T-cells, which are produced in the thymus. Cell-mediated immunity also involves the activation of white blood cells known as phagocytes as well as the manufacture and release of various chemical messengers that orchestrate the overall immune response. The thymus gland is the master control of cell-mediated immunity through its effects on:

• Thymus-derived signaling compounds--The thymus gland releases several hormones such as thymosin, thymopoeitin, and serum thymic factor that regulate many immune functions. Low levels of these hormones in the blood is associated with depressed immunity and an increased susceptibility to infection. Typically, thymic hormone levels will also be very low in the elderly (thymus gland function tends to decrease with age) as well when an individual is exposed to undue stress. Cells that are under the control of the thymus also produce special chemical mediators known as cytokines, which play a huge role in immunity as well as inflammation.

• T cells--There are several types of thymus-derived white blood cells. Cytotoxic T cells are able to directly kill virus-infected cells as well as cancer cells. Helper T cells signal other white blood cells to bring them into the fight. Regulatory or suppressor T cells are important in helping the immune system know the difference between attacking the body's own tissue in an autoimmune response versus attacking an infectious organism or cancer cell.

• Monocytes and macrophages--The thymus gland also helps activate and control these cells that are the garbage collectors of the body. Monocytes are large white blood cells that circulate in the blood. If a monocyte takes up residence in bodily tissues, they are then termed macrophages. Monocytes and macrophages phagocytize or engulf foreign particles including bacteria, viruses and cellular debris and then destroy these particles. Macrophages are essential in protecting against invasion by microorganisms as well as processing what the danger is so that they can send out messages to other cells of the immune system.

• Dendritic cells--These cells are also known as antigen-presenting cells. Their main function is to process viruses and other microbes in a way so that their antigens can be presented in T cells as well as B cells of the immune system. T cells are involved in cell-mediated immunity; B cells make antibodies.

• Natural killer cell or NK cell--These white blood cells received their name because of their ability to destroy cells that have become cancerous or infected with viruses.

It is known quite clearly that low levels of zinc lead to impaired cell-mediated immunity. This occurs as a result of a negative overall effect on thymus function, the synthesis and action of thymus-derived hormones, and on all types of white blood cells. Low levels of zinc not only increases risk for infections, but also allergies, autoimmune conditions and inflammation. Fortunately, zinc supplementation has been shown to reverse these sort of issues caused by inadequate zinc levels on cell-mediated immunity even in what is referred to as "age-related" immune system changes elderly subjects.

Zinc and White Blood Cell Function
All white blood cell types utilize zinc extensively for their individual specialized functions within the immune system. For example, white blood cells involved in cell-mediated immunity are very sensitive to low zinc levels and so to are the white blood cells known as the "garbage collectors" of the body--monocytes, macrophages and neutrophils. These cells play a huge role in protecting against invasion by all types of microbes. They also process what they are destroying so that they can send out messages to other cells of the immune. All of these very important processes of monocytes, macrophages, and neutrophils are zinc-dependent. Anything less than optimal levels of zinc means these processes are not functioning optimally and that could be catastrophic to a person's health.

Zinc As a Direct Antiviral Agent
In addition to its effects on the immune system offering protection against infection, zinc alone in its ionic state exerts direct activity against viruses. However, zinc is not an antibiotic or antiviral drug; rather it is a nutrient that the body uses to fight against organisms as part of our "innate immunity." This term is used to describe defense mechanisms in the body that are naturally present and are not due to activation of the immune system. Zinc is a valuable agent in our innate immunity. That is another reason why it is referred to as the "gatekeeper of immune function." Zinc is especially important in the function of our barriers to infection in our skin and the linings of our respiratory and gastrointestinal tract.

The ability of zinc to fight off viruses as part of our innate immunity is also something that is due directly to zinc as a single molecule. In its free, ionic state, zinc is a powerful component of our innate immune's system fight against infection by directly inhibiting the growth of many viruses. It is not just on our body's barriers, but also within our cells.

Inside cells ionic zinc works in a very elegant way to fight viral infection. When a virus infects our cells, they insert a piece of their genetic code and often an enzyme called replicase to allow the virus to replicate. Zinc, as part of our innate immunity, is able to block the replicase enzyme and, therefore, block the replication or spread of the virus. In order for zinc to have this effect, however, it seems that it is dependent upon an open "ionophore"--a special cell membrane portal (door) that allows for an ion to enter the cell. There are a number of natural compounds that can act as zinc ionophores to aid the intracellular levels of ionic zinc, most notable is the flavonoid quercetin. Natural zinc ionophores like quercetin may assist in increasing intracellular zinc levels.

Usual Dosage
In adults, the dosage range for zinc supplementation for general health support and during pregnancy or lactation is 15 to 20 mg. For children, the dosage range is 5 to 10 mg. When zinc supplementation is being used to address an increased need or bolster host defense mechanisms, the dosage range for men is 30 to 45 mg; for women 20 to 30 mg. There is no need to go beyond this dosage level.

Zinc lozenges are often recommended to boost zinc levels during the common cold. Typically, the dosage recommended for lozenges that supply 15 to 25 mg of elemental zinc is dissolve them in the mouth every two waking hours after an initial double dose. This dosage can be continued for up to seven days. However, because high doses of zinc can impair immune function, avoid a daily intake of greater than 150 mg of zinc for longer than one week.

Available Forms
There are many forms of zinc to choose from. While many clinical studies have utilized zinc sulfate, this form is not as well absorbed. Better forms include zinc picolinate, acetate, citrate, bisglycinate, oxide or monomethionine. There is data to support each of these forms as being very well-absorbed and able to produce benefits. Most zinc lozenges are made with zinc gluconate, which appears to be an effective form for this application.

Possible Side Effects
If taken on an empty stomach (particularly if taking zinc sulfate), zinc supplementation can result in gastrointestinal upset and nausea. Prolonged intake at levels greater than 150 mg per day may lead to anemia, reduced HDL-cholesterol levels and depressed immune function.

Drug Interactions:
Zinc may decrease the absorption of tetracycline and ciprofloxacin. Take any zinc supplement at least two hours before or after taking these antibiotics.

Use of the following drugs increases the loss of zinc from the body or interferes with absorption: aspirin; AZT (azidothymidine); captopril; enalapril; estrogens (oral contraceptives and Premarin); penicillamine; and the thiazide class of diuretics. Supplementation may be required to maintain zinc status in people taking these drugs. VR

Michael T. Murray, ND, is widely regarded as one of the world's leading authorities on natural medicine. A graduate, former faculty member, and serves on the Board of Regents of Bastyr University in Seattle, WA, he is the author of more than 30 books on health nutrition. For more information, visit www.doctormurray.com.