Oct-17-2020

Top nutrients that support the immune system

The immune system mostly lives in the gut. That’s right — about 70 per cent of the immune system is housed in the digestive tract! The immune system is the main link between gut bacteria and their influence on health and disease [1]. Therefore, having a healthy gut — and immune system — depends on the health of one’s gut microbiota and what we put in our body to help (or harm) these friendly bacteria.

Supporting the gut-immune axis with diet

The best way to encourage the growth of healthy gut flora is to consume a diverse diet, specifically one that is high in different types of fibres. Fibre acts a “prebiotic,” or fuel, to feed beneficial gut bacteria. The more resistant starches, pectans, and beta-glucans we can consume — such as in foods like oats, flax seed, onions, garlic, and fruits — the better. In fact, prebiotics like beta-glucans increase host immune defence by activating complement system, enhancing white blood cells (specifically macrophages) and natural killer cell function [2]. Essentially, prebiotics can allow our immune system to better signal our army to fight invading pathogens.

Below are examples of prebiotics (resistant starches) retrieved from Murphy et al.[3] that can easily be added into the diet.

Immune Supporting Micronutrients

Promoting and maintaining a healthy immune system, arguably, couldn’t be more important than it is right now.

Beyond starches, there are chief micronutrients identified as critical for the growth and function of immune cells [4, 5]. Some of these nutrients can be obtained easily through foods and others, not so much. These nutrients include: vitamin C, vitamin D, zinc, selenium, and vitamin A. There are certainly a number of herbs like echinacea, elderberry, and astragalus that also provide immune-enhancing benefits, but this article focuses on micronutrients obtained through diet and possibly supplementation.

Below I dissect each nutrient and how to obtain more in your life:

1. Vitamin C

Vitamin C is able to strengthen the immune system by increasing the production of certain white blood cells. White blood cells are the key players in the immune system since they look for foreign invaders in the blood like bacteria, viruses, parasites, and fungi. The recommended dietary allowance (RDA) of vitamin C is 90 mg, which seems quite low given that vitamin C supplements are typically dosed at 500 mg or 1000 mg per tablet. Comparatively, the amount of vitamin C needed to prevent scurvy — which causes unexpected bleeding and poor wound healing — is 46 mg [6]. So it is clear that “sufficient” vitamin C levels do not equal optimum vitamin C levels, as it is likely that the amount of vitamin C needed to prevent scurvy is not sufficient to optimally protect against disease [6].

Vitamin C can be found in citrus fruits but also in green veggies like broccoli, Brussels sprouts, and green peppers. Guavas, bell peppers, kiwi fruits, and strawberries contain some of the highest doses of vitamin C found in food.

2. Zinc

Zinc is an essential nutrient that is helpful for supporting the immune system, thyroid, and production of testosterone in males. As the gatekeeper of the immune system, zinc has been found to inhibit viral replication and growth. In fact, the adequate function of virtually all immune cells is zinc-dependent [7]. Zinc not only defends against invading pathogens but also protects the human body against an overreactive immune system that can cause autoimmune diseases, chronic inflammation, and allergies [7].

The top zinc-containing foods include animal meat (particularly red med), shellfish, legumes, nuts and seeds, and eggs. Most Canadians can obtain enough zinc from a meat-rich diet.

Pro-tip: supplementing with zinc over the long term can deplete copper in the body because zinc and copper both compete for absorption in the digestive tract. This is why many zinc supplements also contain copper.

3. Vitamin D

Also known as the sunshine vitamin, vitamin D is made by the human body when exposed to adequate levels of sun. Living in a northern latitude like Mississauga means that very little, if any, vitamin D is produced by the body in the winter. In fact, about 40 per cent of Canadians have vitamin D levels below the cut-off in winter months, compared to 25 per cent in the summer months [8]. Since vitamin D is almost exclusively found in animal products — and in low amounts, I might add — vegetarians are at a particularly high risk of not obtaining enough of this vitamin. For most people, the best way to obtain vitamin D is to supplement.

Vitamin D is one of the most important vitamins for immune health. It is a top regulator of the body’s innate immune defence system, our first line of defence against invading pathogens in the body. Several papers suggest that vitamin D plays an important role in the complex relationship between gut bacteria and the immune system [9]. It is responsible for the modulation of the immune system in the bowels, where low levels may be associated with greater gut permeability (i.e., “leaky gut”) which can lead to toxins in the blood (endotoxemia) and low-grade inflammation [9].

4. Selenium

Selenium is a lesser-known nutrient that is vital to overall health. As an essential nutrient, it is only needed in small amounts but is key to thyroid health, immune regulation, heart health, and may even reduce risk of certain cancers [10]. When it comes to immune health, selenium deficiency is associated with lower resistance to infection. Comparatively, increased blood levels of selenium are associated with enhanced immune response against invading pathogens like viruses, bacteria, and fungi.

Obtaining adequate selenium through the diet is possible but may be difficult to control or measure, as the amount of selenium found in a plant is dependent on the soil quantity in which it grew. Brazil nuts are the best source of selenium, where one nut yields between 70-90 mcg of selenium. The recommended daily intake of selenium is just 55 mcg, so one nut technically meets this requirement. However, it’s important to not over-consume Brazil nuts since this can result in selenium toxicity!

5. Vitamin A

Vitamin A is a powerful protector of the body’s mucous membranes, such as the nasal passages, oral cavity, and gastrointestinal tract. Essentially, mucous membranes are where the outside world meets the inside world — and act as a barrier to pathogens found in food or the air we breathe [11]. Vitamin A deficiency is associated with alterations in eye, respiratory, gastrointestinal, and genitourinary epithelial (protective) tissues [11].

There is a common misconception that vitamin A and beta-carotene are the same nutrient. In fact, they are not! While beta-carotene is a precursor to vitamin A, only 8 per cent of beta-carotene in the diet is converted into vitamin A. For this reason, it’s important to include foods in the diet that contain vitamin A, such as eggs, dairy, liver, and fish, or work with your naturopathic doctor to discuss whether supplementing is indicated for you.

If you need help learning how to incorporate these vital nutrients in your diet, or are wondering whether supplementation is the right approach for you, work with your primary care provider such as your naturopathic doctor to develop a customized immune-supporting treatment plan.

Dr. Dominique Vanier is a registered naturopath in Burlington with a clinical focus on digestion, women’s hormones, and menopause. Naturopath Burlington. This article is for information purposes only. It is not intended to treat or diagnose any health conditions.

References:

[1] Wu HJ, Wu E. The role of gut microbiota in immune homeostasis and autoimmunity. Gut Microbes. 2012;3(1):4-14. doi:10.4161/gmic.19320.

[2] Akramiene D, Kondrotas A, Didziapetriene J, Kevelaitis E. Effects of beta-glucans on the immune system. Medicina (Kaunas). 2007;43(8):597-606.

[3] Murphy M, Douglass J, Birkett A. Resistant Starch Intakes in the United States. J Acad Nutr Diet. 2008;108(1):67-78. doi:10.1016/j.jada.2007.10.012.

[4] Guillin OM, Vindry C, Ohlmann T, Chavatte L. Selenium, selenoproteins and viral infection. Nutrients. 2019 Sep;11(9):2101.

[5] Wessels I, Maywald M, Rink L. Zinc as a gatekeeper of immune function. Nutrients. 2017 Dec;9(12):1286.

[6] 2. Anitra C C, Balz F. Toward a new recommended dietary allowance for vitamin C based on antioxidant and health effects in humans. Am J Clin Nutr. 1999;69(6). doi: https://doi.org/10.1093/ajcn/69.6.1086.

[7] Wessels I, Maywald M, Rink L. Zinc as a Gatekeeper of Immune Function. Nutrients. 2017;9(12):1286. Published 2017 Nov 25. doi:10.3390/nu9121286

[8] StatsCan. Retrieved from: https://www150.statcan.gc.ca/n1/pub/82-624-x/2013001/article/11727-eng.htm

[9]Sassi, Francesca et al. “Vitamin D: Nutrient, Hormone, and Immunomodulator.” Nutrients vol. 10,11 1656. 3 Nov. 2018, doi:10.3390/nu10111656

[10] Cai X, Wang C, Yu W, et al. Selenium Exposure and Cancer Risk: an Updated Meta-analysis and Meta-regression. Sci Rep. 2016;6:19213. Published 2016 Jan 20. doi:10.1038/srep19213

[11] Villamor E, Fawzi W. Effects of Vitamin A Supplementation on Immune Responses and Correlation with Clinical Outcomes. American Society for Microbiology. 2005;18(3):446-464. doi:10.1128/CMR.18.3.446–464.2005