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Design by Diego Sabogal

The immune system is a large network of cells, organs, and proteins. It works to protect the body from harmful microorganisms and toxins.

When the immune system works optimally, it does a great job of defending the body. But having a weakened immune system can increase the risk of delayed wound healing, infectious illnesses such as colds, and other infections.

Various vitamins and minerals, often referred to as “micronutrients,” are necessary for a healthy immune system.

The main micronutrients that play a role in the immune response include:

Ideally, we would all obtain optimal amounts of these micronutrients through a well-balanced diet — but this can be difficult to achieve.

Many people worldwide have nutrient deficiencies. In the United States, nearly 95% of the population is not meeting the daily requirements of vitamin D, 84% does not get enough vitamin E, 46% does not get enough vitamin C, 45% does not get enough vitamin A, and 15% does not get enough zinc.

Studies show that even a marginal deficiency in one or more of these vitamins and minerals can lead to impaired immune function.

Many factors, such as stress and infection, can further deplete nutrient stores throughout the body.

Meanwhile, aging increases the body’s demand for micronutrients. People over 50 tend to need more of certain nutrients, including vitamin D, calcium, vitamin B6, and vitamin B12.

To support a healthy immune system and meet nutritional requirements, a person can make sure that their diet is healthy and take a multivitamin that contains 100% of the recommended daily allowance (RDA) of each nutrient.

However, many standard multivitamins may not contain enough vitamin C. Researchers believe that 200 milligrams (mg) a day is necessary for immune health.

If a person already has a deficiency, they likely need more of that nutrient than a multivitamin contains.

Although some studies suggest that supplementation with multiple immune-supporting micronutrients is beneficial, more research is needed.

Currently, the strongest evidence suggests that these three micronutrients offer immune support: vitamin C, vitamin D, and zinc.

Below, we look at what the research says about taking supplements of these nutrients.

Vitamin C

Vitamin C, or ascorbic acid, is a water-soluble vitamin known for its ability to support a strong immune system. In addition to promoting various cellular functions of the immune system, vitamin C helps the body grow and repair tissue, heal wounds, and absorb iron.

Vitamin C is also an antioxidant, meaning that it fights off free radicals, which may help prevent certain cancers and heart disease.

Studies show that a vitamin C deficiency can lead to an impaired immune system and an increased risk of infection.

The human body cannot make vitamin C, so it needs to come from foods or dietary supplements.

The RDA for vitamin C is 90 mg for male adults and 75 milligrams for female adults. However, many scientists believe this is not enough and recommend 200 mg per day for maximum health benefits.

While most studies show that taking vitamin C does not prevent colds in the general population, it may help reduce the symptoms and severity of a cold. For example, one meta-analysis from 2018 found that taking extra doses of vitamin C may help reduce the duration of the common cold by up to half a day, as well as symptoms such as chest pain, a fever, and chills.

Vitamin C supplementation may be even more beneficial for people who perform heavy physical activity. In five trials with 598 total participants, who were exposed to short periods of extreme physical stress, vitamin C reduced common cold risk by nearly 50%.

Vitamin D

Vitamin D plays a critical role in keeping the immune system strong so that the body can fight off bacterial and viral illnesses, such as a cold. Some clinical trials suggest that supplementation of 400 international units (IU), or 10 micrograms (mcg), of vitamin D per day may help prevent the common cold.

Other studies show that vitamin D treatment can reduce respiratory tract infections, especially in those with a vitamin D deficiency.

Some researchers also believe that there is a link between vitamin D deficiency and an increased risk of COVID-19 hospitalization, though there is controversy about this claim. In some cases, it has been used to minimize the impact of socioeconomic factors for at-risk groups.

Many experts believe that the current vitamin D RDA of 600 IU (15 micrograms) for people up to age 70 and 800 IU (20 micrograms) for people over 70 is not enough to support healthy immune function.

However, the evidence remains inconclusive, and finding the dosage that best supports immune function requires further research.

Zinc

A zinc deficiency can weaken the immune system by impairing the formation, activation, and maturation of lymphocytes, white blood cells that are an active part of the immune system.

Several studies suggest that low zinc levels can increase the risk of viral infections. Some also show that zinc lozenges may shorten the duration of the common cold.

However, identifying the best dosages for supporting immune health and treating colds will require further research.

Many have touted probiotics, or “good bacteria,” as another natural way to boost immunity.

We know that they play a key role in helping maintain a healthy balance of bacteria in the gut, and new research supports the idea that they have beneficial effects on immunity.

For example, one study from 2020 — carried out, it must be noted, by a company that produces probiotics — found that probiotic use may reduce the incidence and duration of upper respiratory infections.

The authors call for more research to establish a relationship between probiotics and the immune system.

Many people are taking one or a combination of supplements to prevent or treat COVID-19.

But there is not enough data to support the use of any vitamin, herb, or other supplement to treat or prevent this illness.

Only vaccines, together with strict hygiene measures, are proven to help prevent COVID-19. For severe cases of COVID-19, doctors may use specific medications.

Research does suggest that supplementation with vitamins and minerals can be a low-cost way to support optimal immune function.

Even supplementation with vitamins C and D above the current RDAs may be beneficial to the immune system, as long as dosages stay below the recommended safety limits.

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Many supplements can interact with medications and other supplements. And combining different supplements can also lead to very high amounts of certain nutrients in the body, which can have potentially severe side effects.

For example, excess vitamin C is excreted in the urine and usually causes no serious side effects. But very high amounts can cause diarrhea, abdominal pain, and nausea.

Too much vitamin D — more than 4,000 IU or 100 mcg — can be harmful and lead to nausea, vomiting, kidney stones, confusion, loss of appetite, and muscle weakness.

Very high levels can even lead to kidney failure, an abnormal heartbeat, and death. Vitamin D also interacts with medications, such as the weight loss pill orlistat (Alli, Xenical), steroids, and cholesterol-lowering statins.

If a person has too much zinc, it can cause negative effects such as nausea, vomiting, diarrhea, and headaches. Over time, excess zinc can lead to low copper levels, decreased immunity, and lower levels of helpful cholesterol. Zinc can also interact with other medications.

Probiotics are safe for most people. However, they may worsen illnesses or cause bacterial infections in people who have very weak immune systems or are severely ill.

Having a healthy lifestyle can help the body’s natural defenses and benefit overall health. This can involve:

  • not smoking
  • exercising
  • avoiding excess alcohol consumption, for those who drink
  • washing the hands frequently
  • managing stress well
  • keeping up to date with recommended vaccines
  • having a balanced diet with plenty of fruits and vegetables
  • having a moderate weight
  • getting at least 7 hours of sleep in every 24-hour period

There is no evidence that mega-doses of vitamins and nutrients can boost the immune system. The best way to ensure that the immune system functions well is to have a balanced diet, get enough sleep, exercise, and take the vaccinations that are offered.

Anyone with nutrient deficiencies who is unable to have a healthy, balanced diet may find it beneficial to take a daily multivitamin. But though some research shows that getting more than the RDAs of vitamins C and D might help support immune health, confirming this requires more research.

If a person thinks they have a nutrient deficiency, they should consider speaking with a doctor about having a blood test. This will help pinpoint any deficiencies and determine the right approach to supplementation.

Before taking any supplement, a person should have a conversation with a primary care doctor who is familiar with their medical history.