Our immune systems are made up of many different types of specialized cells, from macrophages to natural killer cells, and like every other cell in the body, they depend on nutrition for optimal functioning—a well-nourished immune system is more resilient and better equipped to handle an infection, lessoning symptoms, duration, and severity. The best plan of action is to take steps early on to enhance your immunity. Many of the supplements listed below should be taken daily to support the healthy functioning of your immune system over the long-term, while others are what to reach for when you first feel something coming on. 

Vitamin C

Vitamin C is a key player in immunity, and it is required by a number of critical immune cells, including white blood cells and natural killer cells, to function properly. It has an impact on both innate and acquired immune responses against infection. Because the human body cannot make vitamin C and this important antioxidant is severely depleted by inflammation, stress, and illness, it is especially important to supplement during times of infection (it is also water soluble, meaning the body does not store it, so it has to be replenished daily). Additionally, vitamin C is similar in structure to glucose and uses the same receptor sites to enter the cell membrane—this means that if you eat a lot of sugar and simple carbs, less vitamin C will be absorbed because glucose is hogging the receptor sites. The key is to maintain optimal levels.

Take: 500-1,000 mg daily for maintenance. This may be increased up to 6,000 mg daily, in divided doses, during times of infection.^{1 2 3 4 5 6}

Vitamin D

Vitamin D plays a central role in proper immune function and is required by our bodies to make a variety of germ-fighting factors, such as the important antimicrobial compound cathelicidin. It has also been shown to reduce the risk of viral infections, such as influenza, pneumonia related to viral infections, and acute respiratory tract infections. Researchers have noted that the winter and early-spring increase in viral infections appears directly related to less seasonal sun exposure and low vitamin D levels, and that those with low vitamin D levels tend to have more serious complications from viral infections like the flu.

Take: 5,000 IU daily for adults, and up to 1,200 IU daily for children.^{7 8 9 10 11 12 13 14 15 16}

Zinc

Like vitamins C and D, this trace mineral is crucial for the proper functioning of the immune system and works synergistically with C and D to support both innate and adaptive immunity. These nutrients are actively used by immune cells to fight infections, including upper respiratory tract infections. Even moderate deficiencies in zinc can increase the risk of infection, and according to one review, “…impaired immune functions due to inadequate zinc status may be the most common cause of secondary immunodeficiency in humans.” Zinc influences the activity of important immune cells like macrophages, neutrophils, and natural killer cells, and also plays a role in immune cell messaging (i.e., it is required for certain immune cells to communicate). Zinc supplementation has been shown to reduce both the risk and duration of pneumonia in children and the elderly, as well as reducing the incidence of infections like the common cold and flu.

Take: 30 mg daily for long-term support. Increase to 50-75 mg daily during times of infection or consider a zinc lozenge for short-term use. Look for zinc picolinate, gluconate, glycinate, or orotate.^{17 18 19}

Probiotics

A large portion of our immune systems are located in our GI tracts, with mounting research indicating that a healthy gut microbiome plays an important role in defending the body against respiratory pathogens, while dysbiosis (an unhealthy imbalance in gut bacteria) can increase the risk of getting a respiratory tract infection. Research has shown that some specific types of probiotics can blunt the symptoms of viral infections in both children and adults: Bifidobacterium bifidum eased cold and flu symptoms in stressed out college students and in a study of children in daycare centers, Lactobacillus rhamnosus GG reduced upper respiratory tract symptoms. Still other research has shown that Bifidobacterium lactis and Lactobacillus brevis can improve cold and flu symptoms.

Take: What the label suggests. Any or all of the mentioned strains should provide preventive benefits when taken long term.^{20 21 22 23 24 25 26}

N-acetylcysteine (NAC)

N-acetylcysteine provides the body with one of the most critical  building blocks to make glutathione, a powerful endogenous antioxidant that protects cells and supports the body’s normal detoxification processes. NAC has also been studied for its impact on immunity. In one study, Italian researchers gave 262 seniors either 600 mg of NAC or placebos twice daily over the cold and flu season. Of the people with lab-confirmed flu infections who were taking NAC, only 25 percent developed symptoms. In contrast, 79 percent of the men and women taking placebos developed clear-cut flu symptoms, according to an article in the European Respiratory Journal.

Take: 600 mg twice daily during the cold and flu season. On the first day of symptoms, increase the amount to 2,400 to 3,600 mg daily and continue until symptoms subside.^{27 28 29}

Quercetin

This flavonoid has been shown to have direct anti-viral action against multiple strains of the flu, in part by preventing the virus’ entry into cells and replication, specifically in the early stages of infection. One study found that the inhibitory effect of quercetin was enhanced when quercetin was already present in the body; in other words, it works most effectively when it’s taken before you get a viral infection. In addition to its anti-viral action, quercetin also supports a healthy inflammatory response by downregulating cytokine expression and secretion. In animal models, quercetin has been shown to reduce viral-induced inflammation, lung inflammation, improve lung function, and reduce the damaging effects of oxidative stress on the lungs.

Take: 1,000 mg daily, in divided doses.^{30 31 32 33}

Oscillococcinum^®

The homeopathic remedy oscillococcinum (pronounced os-sil-uh-cox-suh-num) can reduce flu symptoms, particularly body aches, headaches, fever, and chills, when you’ve already caught the virus. A Cochrane review described it as a “promising” remedy and noted that it “probably reduces the duration of illness in patients presenting with influenza symptoms.”³⁴

Take: Follow label directions, starting on the first day of symptoms.

Elderberry

Elderberry (Sambucus nigra) can quickly reduce the aches, pains, and fatigue that accompanies the flu. In one study, researchers found that 14 of 15 people taking elderberry extract had a significant reduction in symptoms, including fever, after just two days, and 13 of the 15 patients were symptom free after three days.^{35 36 37} Most of the studies have used an elderberry syrup.

Take: Follow label directions, staring on the first day of symptoms.

Echinacea

This popular herbal remedy works wonders when it comes to reducing the odds of catching a cold or flu, and it also seems to ease symptoms if you’ve already caught something. An analysis of 14 human studies, published in Lancet Infectious Diseases, found that echinacea supplements slashed the odds of catching a cold by an impressive 58 percent. For people who did catch a cold, the herb cut its duration by a day and a half.³⁸

Take: Follow label directions.

While there is no guarantee that you won’t ever get sick, priming your immune system now with the right nutrients will give you an edge, so even when you do get sick, your immune system is ready to work hard to get you back to good health!

Strong Immunity, What’s Blood Sugar Got to Do With It?

Keeping your blood sugar levels in a healthy range determines how well your immune system is able to mount an attack against all types of pathogens, whether viral or bacterial. Chronically high blood sugar causes major dysfunction in both innate and adaptive immunity, and research has found that some viruses and bacteria are “better nourished and become more virulent” in the presence of high blood sugar, which provides them with a better environment to cause infection in the first place.³⁹ Even if you are an overall healthy person, if you eat sugar when you are sick, or are first starting to feel sick, that sugar will undermine your immune response, in part because glucose blocks vitamin C from entering your cells, and vitamin C is a critical immune-supportive nutrient, especially during acute infection.⁴⁰ When you maintain healthy blood sugar levels, you also support the optimal functioning of your immune system.

References

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