Top Nutrients for Immune System Support

Vitamin C

Vitamin C (ascorbic acid) has strong immune-supportive actions. Because the body doesn’t make vitamin C, you must consume food or supplements that contain it to meet your body’s needs. Scurvy, a severe form of vitamin C deficiency, was cured in the 1700s by eating oranges and lemons, although it wasn’t until the 1930s when vitamin C was isolated as the citrus fruit nutrient that prevents the disease. 

Today, although a deficiency as severe as scurvy is extremely rare, suboptimal levels of vitamin C can occur when the body works overtime to protect itself against the numerous free radical exposures of modern life. An obvious example of this is that the daily recommended vitamin C intake is higher for smokers than non-smokers, due to the increased oxidative stress from toxins in tobacco products.¹

External toxins are not the only sources of free radicals that vitamin C protects against. As your body functions in daily living, free radicals are produced by normal immune function and metabolic action. Vitamin C protects cells and tissues in your body, as well as DNA, proteins, lipids, and carbohydrates, all of which are necessary for healthy functioning. And if that wasn’t enough, vitamin C also works to recycle other antioxidants, like vitamin E, so they can be used again to protect against oxidative stress.¹

Vitamin C also supports a variety of other immune system functions. It stimulates your body to produce white blood cells, including lymphocytes and phagocytes, and enhances the ability of white blood cells to move to where they are needed to kill invading microorganisms. White blood cells also store high concentrations of vitamin C to protect themselves from the oxidative stress that occurs when phagocytes are working to kill invaders.²

Along with targeting and removing disease-causing microbes, your immune system is also responsible for healing and repair. Vitamin C is necessary for the body to make collagen, a protein that is the building block for connective tissues like skin, cartilage, tendons, and bones. Cuts, scrapes, surgical incisions, and broken bones all require vitamin C to heal correctly.¹

Vitamin D3

Vitamin D is a fat-soluble vitamin, meaning it only dissolves in fats or oils, and not water. Your body stores some fat-soluble vitamins in various tissues to access them when needed, but you still must make vitamin D or consume fat-soluble vitamins in your diet or as nutritional supplements to ensure adequate amounts are available for healthy functioning. 

Vitamin D is necessary for healthy bones and teeth, where it acts by regulating the activity of calcium and phosphorus. In addition, healthy insulin secretion and blood pressure regulation both rely on an adequate level of vitamin D. Another important function of vitamin D is a process called differentiation.

As your body produces new cells for growth, wound healing, and repair, these cells need to be specialized for their specific functions. The differentiation process also decreases the overgrowth of cells, particularly those with mutations.³

In the immune system, vitamin D acts as a modulator, meaning it helps to keep the immune system in check – ramping up function when necessary and calming the immune response when its work is done.² Vitamin D helps to bring neutrophils – a type of phagocyte – to the site of infection, which leads to increased oxidative burst, a mechanism by which neutrophils eliminate invaders.⁴

When skin is exposed to sunlight, ultraviolet-B (UVB) waves stimulate the body to make vitamin D. Several factors affect your body’s ability to make vitamin D. The time of day, time of year, and your location on the planet all make a difference in the amount of UVB rays available to you to absorb.

Melanin, the pigment in human skin, also absorbs UVB rays, which limits the ability of UV light to trigger vitamin D production. Thus, individuals with darker skin are more susceptible to having lower vitamin D levels. Use of sunscreen and protective clothing can also decrease vitamin D production by limiting the amount of UVB exposure.³

Aside from the vitamin D your body can make, its main food sources are fatty fish, like sardines, salmon, and mackerel. There are also vitamin D-enriched foods (vitamin D is added to them) such as milk, orange juice, cereals, and egg yolks from chickens that have been fed vitamin D. For individuals who follow a vegan diet, high-quality dietary sources of vitamin D can be limited.

In addition, many vitamin D3 supplements are made from lanolin (sheep’s wool) or contain ingredients like lactose that are not suitable for a vegan diet or for someone who is lactose intolerant.  Vegan vitamin D3 is sourced from algae, the same source that makes the fatty fish that eat it a good source of vitamin D3.

Zinc 

Zinc is an essential mineral – your body doesn’t make it – so it must come from food and supplementation. Within your body, zinc is necessary for growth and development, immune function, and healthy hormone levels. Hundreds of enzymatic reactions require zinc to function properly.

Your immune system depends on zinc for the development and healthy functioning of lymphocytes and phagocytes.² Although zinc is well-studied to provide immune support when you don’t feel your best, the type of zinc makes a difference. Zinc that contains certain types of additives are not well absorbed.⁵

Zinc also has important antioxidant functions. Along with copper, it forms an enzyme called copper-zinc superoxide dismutase (SOD1), which helps break down free radicals inside cells, thus decreasing oxidative stress that causes damage over time. In addition, zinc has an important role in collagen synthesis, similar to vitamin C, which makes zinc an important nutrient for wound healing and tissue repair.^2,5

The best food sources of zinc are often animal sources like oysters, beef, and poultry, and while there are plant-based sources, such as beans, nuts, and seeds, phytic acid in plants can bind-up zinc, decreasing its bioavailability. Those who follow a vegan diet, the elderly, and elite athletes can be at risk for a zinc deficiency due to poor absorption, inadequate intake, or excessive loss of zinc through sweating.

Quercetin 

Quercetin is a type of antioxidant known as a flavonoid, which are most often found in fruits and vegetables and contribute to their beautiful colours. Flavonoids protect your body against free radicals and regulate the activity of certain cells. Capers have the highest natural concentration of quercetin of all food sources, but a variety of fruits and vegetables, including apples, onions, grapes, berries, and broccoli, are also good sources.⁶

Much like vitamin D, quercetin is an immune system modulator, increasing the activity of some white blood cells, while stabilizing or decreasing the activity of others. Quercetin is most well-known for stabilizing mast cells – histamine-releasing cells that cause many allergy-related symptoms. Quercetin also has a positive effect on maintaining a healthy inflammatory response by modulating the release of cytokines – molecules that help immune cells communicate with each other, thus coordinating the immune response.^6,7

Although quercetin is present in many fruits and vegetables, it tends to have differences in absorption based on its source. For example, the type of quercetin found in onions tends to be better absorbed than the type found in tea. In addition, quercetin is not soluble in cold water, and hot water improves its solubility only a little, while alcohols and fats greatly increase its ability to be absorbed.⁶ So when supplementing quercetin phytosome, it’s important to consider the source.