Vitamin D is a fat-soluble vitamin that plays a number of critical roles in your body.

This nutrient is especially important for immune system health, leaving many people wondering whether supplementing with vitamin D may help reduce the risk of contracting the new coronavirus that causes COVID-19.

While antivirals like Paxlovid show promise as a treatment for COVID-19, preventive measures like physical distancing and proper hygiene can protect you from contracting the virus.

Also, some research shows that having healthy levels of vitamin D can help keep your immune system healthy and may protect against respiratory illnesses in general.

This article explains how vitamin D affects immune health and how supplementing with this nutrient may help protect against respiratory conditions.

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How does vitamin D affect immune health?

Vitamin D is necessary for the proper functioning of your immune system — which is your body’s first line of defense against infection and disease.

This vitamin plays a critical role in promoting immune response. It has both anti-inflammatory and immunoregulatory properties, and is crucial for the activation of immune system defenses (1).

Vitamin D is known to enhance the function of immune cells, including T cells and macrophages, that protect your body against pathogens (2).

In fact, the vitamin is so important for immune function that low levels of vitamin D have been associated with increased susceptibility to infection, disease, and immune-related disorders (3).

For example, low vitamin D levels are associated with an increased risk of respiratory diseases, including tuberculosis, asthma, and chronic obstructive pulmonary disease (COPD), as well as viral and bacterial respiratory infections (4, 5, 6, 7).

What’s more, vitamin D deficiency has been linked to decreased lung function, which may affect your body’s ability to fight respiratory infections (8, 9).

Summary

Vitamin D is critical for immune function. A deficiency in this nutrient may compromise immune response and increase your risk of infection and disease.

Can taking vitamin D protect against COVID-19? 

Few studies have investigated the effect of vitamin D supplements or vitamin D deficiency on the risk of contracting COVID-19.

Still, studies have shown that vitamin D deficiency may harm immune function and increase your risk of developing respiratory illnesses (10).

Additionally, some studies have indicated that vitamin D supplements can enhance immune response and protect against respiratory infections overall.

A recent review that included 11,321 people from 14 countries demonstrated that supplementing with vitamin D decreased the risk of acute respiratory infections (ARI) in both those who had deficient and adequate levels of vitamin D.

Overall, the study showed that vitamin D supplements reduced the risk of developing at least one ARI by 12%. The protective effect was strongest in those with low vitamin D levels (11).

Moreover, the review found that vitamin D supplements were most effective at protecting against ARI when taken daily or weekly in small doses and less effective when taken in larger, widely spaced doses (12).

Vitamin D supplements have also been shown to reduce mortality in older adults, who are most at risk of developing respiratory illnesses like COVID-19 (13).

What’s more, vitamin D deficiency is known to enhance a process known as the “cytokine storm” (14).

Cytokines are proteins that are an integral part of the immune system. They can have both pro-inflammatory and anti-inflammatory effects and play important roles, helping protect against infection and disease (15, 16).

However, cytokines can also induce tissue damage under certain circumstances.

A cytokine storm refers to the uncontrolled release of pro-inflammatory cytokines that takes place in response to infection or other factors. This dysregulated and excessive release of cytokines leads to severe tissue damage and enhances disease progression and severity (17).

In fact, it’s a major cause of multiple organ failure and acute respiratory distress syndrome (ARDS), as well as an important factor in the progression and severity of COVID-19 (17).

For example, patients with severe cases of COVID-19 have been shown to release large numbers of cytokines, particularly interleukin-1 (IL-1) and interleukin-6 (IL-6) (18).

Vitamin D deficiency has been associated with reduced immune function and may enhance the cytokine storm.

As such, researchers postulate that a vitamin D deficiency may increase the risk of severe COVID-19 complications, as well as that vitamin D supplementation may reduce complications related to cytokine storms and uncontrolled inflammation in people with COVID-19 (19, 20).

Currently, multiple clinical trials are investigating the effects of vitamin D supplementation (at dosages up to 200,000 IU) in people with COVID-19 (19, 21).

Although research in this area is ongoing, it’s important to understand that taking supplemental vitamin D alone can’t protect you from developing COVID-19.

However, being deficient in vitamin D may increase your susceptibility to overall infection and disease by harming immune function.

This is especially worrisome given that many people are deficient in vitamin D, especially older individuals who are most at risk of developing serious COVID-19-related complications (22).

For these reasons, it’s a good idea to have your healthcare provider test your vitamin D levels to determine whether you have a deficiency in this important nutrient. This is particularly important during winter months.

Depending on your blood levels, supplementing with 1,000–4,000 IU of vitamin D per day is typically sufficient for most people. However, those with low blood levels will often require much higher doses to increase their levels to an optimal range (23).

Though recommendations on what constitutes an optimal vitamin D level vary, most experts agree that optimal vitamin D levels lie between 30–60 ng/mL (75–150 nmol/L) (24, 25).

Summary

Though research continues, evidence that vitamin D supplements reduce the risk of developing COVID-19 is still limited. Having healthy vitamin D levels can enhance immune health and may be helpful in people with COVID-19.

The bottom line

Vitamin D plays many important roles in your body, including promoting the health of your immune system.

Scientific research suggests that supplementing with vitamin D may protect against respiratory infections, especially among those who are deficient in the vitamin.

Recent research indicates that sufficient vitamin D levels may help people with COVID-19 avoid adverse outcomes.

Still, we don’t know whether taking vitamin D supplements reduces your risk of developing COVID-19 as a result of contracting the coronavirus.

Talk to your doctor about supplementing with vitamin D to enhance your overall immune response.