The A’s and B12’s of Immunity: How Nutrition Affects Immune System Function

This article was originally published in the September 2018 issue of AromaCulture Magazine (www.aromaculture.com) and has been adapted for use here with permission from the publisher.

Nutrition is well known to be an important factor for immune system function. In fact, malnutrition is the leading cause of immunodeficiency worldwide (Chandra, RK, 2007). Although developing a deficiency in a single nutrient is uncommon, clinical studies show that even mild deficiencies can negatively affect immune system function (Chandra, RK, 2007). This may manifest as an increased frequency of colds and flus, genital, and urinary tract infections (Chandra, RK, 2002). 

With exception to people in at risk groups, such as the elderly and those in clinical immunocompromised states, eating a varied, whole foods diet is usually simpler and more effective than supplementing to ensure you are getting a rounded variety of nutrients to take care of your immune system (Chandra S, Chandra RK).

Understanding the Immune System

The immune system is generally divided into two categories: innate, and acquired - sometimes called humoral. The innate immune system is the first line of defence, and consists of the skin, mucosal barriers, enzymes such as those in saliva and stomach acid, and generalized immune cells such as macrophages, leukocytes, natural killer cells (NK cells), and dendritic cells. These are cells that directly kill any foreign pathogens and material that they don’t recognize as part of the body. (Wintergerst ES et al)

If the innate immune system fails to prevent infection, the adaptive immune system steps up (Wintergerst ES et al). These are specialized T and B lymphocytes, named for whether they mature in the thymus gland or the bone marrow (Wintergerst ES et al). These cells make up antibodies, memory cells that recognize past infection and can quickly react to subsequent exposure (Wintergerst ES et al). The adaptive immune system has a more complex system. It uses signalling molecules called cytokines and interleukins which act like hormones to trigger an inflammatory response, reactive oxygen species (ROS) to weaken pathogens, and inflammation (Wintergerst ES et al). All components of the immune system are vulnerable to deficiencies, from barrier integrity, to phagocytosis and antibody production, to the ability to deal with excessive ROS (L.C. Carmen).

In addition to circulating in the lymph and bloodstream, immune cells are also present in the skin and epithelial lining of the gut, lungs, and reproductive tract (Wintergerst ES et al). The gut is in fact considered the largest immune organ in the body, referred to as GALT (gut-associated lymphoid tissue) (Wintergerst ES et al). The health of the gastrointestinal tract itself will affect absorption of nutrients and therefore immune function, but of equal importance is the health of the microbiome (Forchielli ML, Walker WA). The composition of gut bacteria has been shown to influence not only gastric immune cells, but mucosal immune cells at distal sites as well (AJ McDermont, GB Huffnagle) One of the ways a healthy microbiome interacts with the immune system is by producing short-chain fatty acids and other metabolites that induce inflammatory mediators, and help to produce a balanced T-helper response (Forchielli ML, Walker WA). 

Nutrients and their effects on the Immune System

It is difficult to study the effects of diet overall on immune health, so most studies are carried out on single nutrients. The nutrients that are known to directly affect the immune system are essential amino acids, folic acid, vitamins A, C, E, B6, B12, zinc, copper, iron, and selenium. (Calder PC, Kew S),(Wintergerst ES),(Maggini S et al) ​

Innate immunity - barrier integrity

Vitamins A, C, D, E, and zinc are all directly related to skin barrier and epithelial mucous membrane integrity and function (Maggini S et al). For example, vitamin A is involved in gene expression and differentiation of epithelial tissue, therefore regeneration of the tissue is impaired with deficiency, as is its ability to fight extracellular infections. (Wintergerst ES),(Maggini S et al). When there is a deficiency in any of these nutrients, as shown in studies of vitamins A, and D, there will be a higher frequency of infections in the eyes, respiratory tract, and gastrointestinal tract (Maggini S et al). Increasing vitamin A levels in children in developing countries has resulted in fewer deaths from measles, diarrheal disease, acute respiratory infections, malaria, and tuberculosis (Maggini S et al). 
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Vitamin D in particular is protective to the respiratory tract; we notice this in the winter months when a lack of sunlight causes increased lung infections (Maggini S et al). Alternatively, using cod liver oil or UV exposure during the winter decreases susceptibility to respiratory infections (Maggini S et al). This happens because vitamin D stimulates production of generalized immune cells that are present in the mucous lining of the lungs and respiratory tract (Maggini S et al). It is vital to every part of the immune system, as there are vitamin D receptors on most immune cells (Maggini S et al).

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Innate immunity - generalized immune cells

As with the previous section, vitamins A, C, D, E, and zinc, with the inclusion of copper and iron have important roles in the function and production of the various generalized immune cells and phagocytosis (Wintergerst ES),(Maggini S et al).​ There are a significant number of vitamin D receptors on monocytes, macrophages, and thymus tissue, suggesting a vital role of vitamin D in immune system function and immune cell production and maturation (Maggini S et al)(Barbara Prieti et al). Although vitamin D stimulates production of monocytes, antimicrobial peptides, NK cells, and neutrophils in the lungs (Maggini S et al), it appears to have an immunomodulatory role on the innate immune system - particularly on monocytes and antigen-presenting cells (Barbara Prieti et al). This has important implications in autoimmune diseases, which are vulnerable to an overactive immune system (Barbara Prieti et al).

Iron influences cell differentiation and growth, including immune cells, however, an  overabundance of iron can actually feed the pathogen, so supplementation should only be used in iron-deficient states. (Maggini S et al)

Acquired immunity

All nutrients mentioned in this article except for vitamin C and iron are used in antibody production, while B6, selenium, copper, and zinc have a direct impact on it (Wintergerst ES),(Maggini S et al). The latter nutrients also have a direct impact in particular on B-cell proliferation; these particularly good with extracellular pathogens (Maggini S et al).

Vitamin D again is an important nutrient in adaptive immune system function. Vitamin D enhances calcium and phosphate absorption and promotes mineralisation of bone. Because immune cells originate in the bone marrow, healthy bones will produce healthy immune cells. During active infections, both T and B lymphocytes upregulate vitamin D receptors, and there is evidence that calcitriol acts in a suppressive way on B cells in the same way that T-suppressor cells work, which can again have important implications in autoimmunity. (Barbara Prieti et al)

Vitamins B6, B12, and Folate work together in protein synthesis.  A deficiency in any of these three vitamins results in decreased T-lymphocyte maturation and proliferation, as well as antibody and cytokine production. Selenium activates the expression of genes that code for cytokines and various other proteins involved in the immune response. (Maggini S et al)

Vitamin C

ROS are a normal byproduct of immune system function. They are created during inflammation and are used to kill bacteria and pathogens, but every cell in the body is vulnerable to oxidative stress. Vitamin C is an effective antioxidant that scavenges free radicals therefore controlling oxidative stress, and regulating inflammation. Vitamin C is rapidly used up during infection, as high concentrations of ROS can impair immune response even though they are used in immune response. Studies show that increased vitamin C intake can significantly reduce the duration and severity of cold and flu symptoms, though will not prevent infection in the first place. (Maggini S et al)

Healthy Dietary Sources

Now that we know which specific nutrients are important for the immune system and why, if you are noticing in yourself or in your clients a potential immune deficiency, through looking at their diet we can find what they may be missing. We often hear about the importance of eating a “varied, whole foods diet”. But what does eating whole foods mean? Unprocessed whole grains are grains with the outer shell, or hull, included. Whole grains have substantially more minerals, vitamins, and other nutrients compared to refined, hulled grains (Pritchford). When comparing vegetables, some studies have found that organically grown plants contain up to 90% more minerals than conventionally grown (Pritchford).

Similarly to conventionally grown plants, farmed fish contain less healthy fats and are more susceptible to infection, even when organically fed, than wild fish do (Pritchford). The same can be said for grass-fed beef over grain fed, the former having a higher fatty-acid content, and a higher content of omega 3 precursors (Cynthia A. Daley et al). 

It appears that by simply changing to organic whole foods, with grass-fed beef or wild fish, you can already start to increase your nutrient profile, though this is not always possible for every demographic. Here, we can generally stick to locally sourced food, and think about which foods contain the highest levels of the immune-specific nutrients. This information is easily found online, but as a general rule, there are high levels of minerals and B vitamins in dark green, leafy vegetables, while orange and red pigments are rich in Vitamin A (Dieticians of Canada, 2018).  Of course, in all cases it is important to remember to take care of your gut health.

References

1. Laurdes C. Carman, M.D “The Relationship Between Nutrition, Infection, and Immunity” symposium on clinical immunology i, 1985
2. Andrew J McDermott and Gary B Huffnagle “The microbiome and regulation of mucosal immunity” immunology, 2014
3. Dietitians of Canada, https://www.dietitians.ca/, 2018
4. Forchielli ML, Walker WA, “The role of gut-associated lymphoid tissues and mucosal defense” british journal of nutrition, 2005
5. Calder PC, Kew S. “The immune system: a target for functional foods?” british journal of nutrition, 2002
6. Wintergerst ES, Maggini S, Hornig DH. “Contributions of selected vitamins and trace elements to immune function” annuls of nutrition & metabolism, 2007
7. Maggini S et al, “Selected vitamins and trace elements support immune function by strengthening epithelial barriers and cellular and humoral immune responses.” british journal of nutrition, 2007
8. Chandra, RK “Nutrition and the immune system: an introduction” the american journal of clinical nutrition, 2007
9. Chandra, RK “Nutrition and the immune system from birth to old age” european journal of clinical nutrition, 2002
10. Chandra S, Chandra RK “Nutrition, Immune Response, and Outcome” progress in food and nutrition science, 1986            
11. Barbara Prieti et al “Vitamin D and Immune Function” nutrients, 2013
12. Cynthia A. Daley et al “A review of fatty-acid profiles and antioxidant content in grass-fed and grain-fed beef” nutrition journal, 2010
13. Paul Pritchford, Healing with Whole Foods, Asian Traditions and Modern Nutrition, Third Edition, north atlantic books california, 2002