Nutrients This Dietitian Swears By To Keep Your Immune System Strong

Are you doing everything you can do to keep your immune system up to par? That's a huge question because the 70 trillion cells throughout your entire body are involved in immune system function, and many exterior factors also influence immune strength, such as stress and sleep. 

From a nutrition standpoint, check out these top nutrition tips to stay healthy all year long.

Vitamin C

Vitamin C tops the list of immune-supporting nutrients. It's involvement in immune function has long been known and there's more research about the immune-supporting effects of Vitamin C than perhaps any other nutrient. Concentrations of this vitamin in the body’s white blood cells (the major immune cell type of the body) become rapidly depleted during infections, making it important to consume adequate amounts of vitamin C. When combined with zinc, vitamin C shows its abiilty to support GI and respiratory health (13).

Vitamin C is available naturally in many fruits and vegetables, particularly in guava, papaya, strawberries, kiwi, cantaloupe, orange, lemon, and grapefruit (1). Unlike most animals that produce their own Vitamin C, the human body does not synthesize any.

Along with eating vitamin-C containing foods in your kitchen, take 500 to 1,000 mg throughout the day with meals and snacks. I like to use a liquid or vitamin C powder I can mix in water or smoothies. If you prefer capsules, get 2500 mg vitamin C in one scoop of Lysine-C.

One word of caution, vitamin C can increase iron absorption and in susceptible individuals could result in iron overload.

Vitamin D

Vitamin D is more like a hormone, not a true vitamin, and it is responsible for modulating the peripheral immune system and the innate immune system in the central nervous system. To say the least, ensure your body's vitamin D levels are adequate is essential. 

During the winter months, vitamin D supplementation is strongly encouraged. During the summer months, if you're indoors a lot or regularly slather up with sunscreen, you may need to supplement with vitamin D as well. 

Don't forget vitamin K2 since it's ideal to take vitamin D3 and K2 together. From a bone standpoint, it's well known vitamin D assists calcium absorption, but vitamin K is what guides the calcium to bones and prevents its absorption into organs, joint spaces and arteries, including heart arteries, which can be problematic. The combined approach not only benefits bone and cardiovascular health, but overall health as well.

It is best to get your levels of 25-OH vitamin D checked for accurate dosing. An optimal range is around 70 ng/mL. Many people need 5,000 IU or more of vitamin D3 a day in the winter. Start with 2,000 IU for adults, 1,000 IU for children. I like this D3/K2 chewable vitamin, which my kids also take easily. It tastes good and dissolves very quickly in the mouth.


Zinc is an essential mineral, and it is necessary for immune support inside each and every cell of the body! Zinc supports healthy production of white blood cells. Consuming zinc by itself is not effective. Rather than getting inside the cells where it’s needed, the zinc remains outside the cell (a little gets in, but not enough). When a virus lives inside the cells of the body, the zinc must be able to get to it. Zinc is most effective in combination with a zinc ionophore, such as quercetin or EGCG.

As little as 15 to 25 milligrams a day will help to support immune function, but for extra immune support aim for 30 mg zinc per day. Some of the top zinc-containing foods are seafood (oyster, crab), grass fed beef, pumpkin seeds and beans (8). Read more here about the additional functions of zinc.

Vitamin A

Vitamin A is a pro-hormone immune modulator, and is important for mucus membranes, which are some part's the body's first line of defense. What this means is it's not officially a hormone but acts a whole lot like one. Vitamin A supports the immune cells in our body known as phagocytes (neutrophils and macrophages), so supplementing vitamin A supports the immune system.

Beta carotene, from sweet potatoes, carrots and pumpkin, is an antixodiant studied to support the number of natural killer T-cells in our immune system. As a powerful antioxidant, beta-carotene fight and help remove free radicals that can accelerate illness (7). 

However, it’s important to realize that the form of vitamin A found in plants (beta-carotene) is not an active, usable form of vitamin A. It is critical to get vitamin A in its active form, called retinol. Why? Because not everyone can adequately convert the inactive form found in fruits and vegetables (beta-carotene) into the active form (retinol).


A healthy gut flora supports a healthy gut, which is a major barrier against pathogens and integral to the immune system. Having a healthy supply of gut flora also supports a person's white blood cell production and activity. Probiotics may support immunity while taking antibiotics, and they supply added support to those who may have a compromised immune system.

Probiotic rich foods include yogurt, kefir, select cheeses and milk, sauerkraut, kimchi and tempeh (2). Look for brands that offer several species of good bacteria and contain at least Lactobacillus plantarum and spore forms of Bacillus are the best for immunity. 

Fish Oil or Arctic Cod Liver Oil

This age old remedy for good health and robust immunity still holds! In addition to the healthy omega-3 fats, cod liver oil contains vitamin A and D, which offer added immune support. If you don't like the flavor of cod liver oil, give fish oil capsules a try.

Omega-3 fats can be found in ground flaxseed and fish such as, salmon, tuna, sole, flounder, sardines, herring and mackerel (10). Consider taking a fish oil or cod liver oil supplement on days you aren't eating a serving of low-mercury fish.

Green Tea

Green tea contains 4 major phytonutrients called catechins. They offer antioxidant protection and promote the body's innate resistance to pathogens. One catechin in particular, EGCG (epigallocatechin gallate), is responsible for green tea's immune promoting components (11, 12). These catechins exert their immune-supporting activity by binding to bacterial cell membranes. As a result, the bacteria often loses its ability to bind to the host (human) cells. The other amazing thing is that by damaging the bacterial cell wall, bacteria lose their ability to use quorum sensing to create biofilms. Biofilms are what happen when pathogens join forces to hide and get stronger so the ability for the immune system


The immune supporting properties of garlic seem to be due to its sulfur-containing compounds (organosulfur). These unique compounds seem to promote the body’s innate resistance to pathogens and maintain the normal homeostasis of the immune system. Garlic can also act as an antioxidant that reduces the build-up of free radicals in the bloodstream (9). One of my favorite ways to eat garlic is in pesto. To maximize the health benefits of garlic, crush or slice all your garlic before you eat it because this increases the allicin content. Before you cook with your crushed garlic, let it stand for 10 minutes, and use a lot of garlic — more than one clove per meal, if you can.

The goal is to provide your immune system the TLC it needs all year long, not just during a particular vulnerable season. You can get seven out of the eight immune supporting nutrients from the foods in your kitchen. Vitamin D is the exception, so get outside and don't be afraid to take a supplement.  

Stay well,

Kelly Harrington, MS, RDN
Registered Dietitian Nutritionist for Healthy Goods



1. US National Library of Medicine National Institute of Health (NIH). Dietary Supplement Fact Sheet: Vitamin C. 

2. National Products Foundation Vitamins and Herbs A-Z: Probiotics. 

3. US National Library of Medicine National Institute of Health (NIH). Dietary Supplement Fact Sheet: Selenium.  

4. National Products Foundation Vitamins and Herbs A-Z: Selenium.

5. National Products Foundation Vitamins and Herbs A-Z: Beta-Glucan.

6. US National Library of Medicine National Institute of Health (NIH). Dietary Supplement Fact Sheet:  Vitamin E.

7. National Products Foundation Vitamins and Herbs A-Z: Beta-Carotene. 

8. US National Library of Medicine National Institute of Health (NIH). Dietary Supplement Fact Sheet: Zinc.

9. National Products Foundation Vitamins and Herbs A-Z: Garlic. 

10. National Products Foundation Vitamins and Herbs A-Z: Fish Oil & Cod Liver Oil (EPA & DHA). 

11. Rowe C A, et-al. Specific formulation of Camella sinensis prevents cold and flu symptoms and enhances gamma delta T cell function: A randomized, double-blind, placebo controlled study. J Am Coll Nutrition, 2007, 26: 445-452.

12. J Bukowski et-al. L-theanine intervention enhances human gamma delta T lymphocyte function. Nutr Rev, 2008, 66: 96-102.


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