What Does Vitamin D Have To Do With COVID-19?

If you’ve been wondering these days if you should start taking a vitamin D supplement, you’re not alone! Vitamin D has been getting a lot of press lately, for its potential in treating and/or preventing respiratory illnesses, including COVID-19. Is it true? Let’s break down the science.

What is Vitamin D?

Vitamin D is a fat soluble vitamin, and also functions as a hormone. It isn’t present naturally in many foods, but it is added to some, and available as a supplement. The skin can also use ultraviolet light to make vitamin D from cholesterol in the body.

Vitamin D helps to promote calcium absorption to keep bones strong, as well as helping in cell growth, immune function, and inflammation reduction (1). A vitamin D deficiency over time can lead to the development of rickets in children, and osteomalacia in adults.

Vitamin D and Immunity

Most of us know vitamin D for its importance to bone health, but vitamin D has also been studied for years for its role in immunity. As early as 1926, it was observed that when people were exposed to sunlight, their number of respiratory infections decreased. It was then thought that the lack of solar radiation during the dark winter months may be responsible for some kind of a vitamin disorder (2). We now know this to be vitamin D, and that people living further from the Equator generally have more vitamin D deficiency because of lower sun exposure.

Studies now suggest the vitamin may play a role in immune response and controlling inflammation, particularly in the lungs.

Vitamin D is needed for the production of two immune system proteins, called defensins and cathelicidins (3). Defensins and cathelicidins are two major families of antimicrobial proteins that mammals, including humans, have. They have the ability to kill or inactivate bacteria, fungi, and enveloped viruses (4).

Vitamin D supplementation has been shown to increase production of these molecules; mainly cathelicidins, and to a lesser degree defensins (5).

Vitamin D and Respiratory Infections

With regard to respiratory infections, low vitamin D status has been linked to both increased risk of contracting a viral respiratory infection (6, 7, 8), and an increased length of viral respiratory infections (8, 9).

One study found the majority of people who developed acute respiratory distress syndrome were vitamin D deficient. These patients seemed to develop an increased inflammatory response to respiratory infections, leading to the syndrome (10). Other studies and reviews have similar findings, noting that people with vitamin D deficiency are more likely to have lung conditions like asthma and COPD, develop respiratory infections, and have worse outcomes, up to and including death, when those infections occur (11, 12, 13).

Another review of studies suggested supplementation with vitamin D can protect against respiratory infections, but cautioned there could be publication bias affecting those studies (14). All studies done note that the benefit of vitamin D supplementation was only seen in people with a vitamin D deficiency. Taking a vitamin D supplement without a deficiency was not seen to be beneficial.

Can Vitamin D Supplements Protect Me Against COVID-19?

Since COVID-19 is a relatively new virus, there aren’t many studies to look at. But we do have some observational data.

One report noted populations living below 35 degrees latitude North are having better outcomes and less death related to the virus. The authors think this could be because of more sunlight exposure, and better vitamin D statuses of those populations (15). The report also notes vitamin D deficiency is related to other factors that can lead to more severe COVID-19, including hypertension, diabetes, obesity, and ethnicity.

The study receiving much of the attention lately, however, is one published in April 2020, suggesting that vitamin D deficiency is correlated with an increased risk of dying from COVID-19 (16). It is worth noting that this study has not yet been peer reviewed, which is an important step for research to be vetted and accepted into publication. While the conclusions of the authors sound promising, the study has some major limitations. Most importantly is that, due to the novel nature of the virus, it was impossible to design and conduct an experiment in such short order. Because of this, the authors used data from other studies on population demographics, disease states, and vitamin status. They had to make the assumption that population characteristics from those studies match the current population affected by COVID-19. This may or may not be the case. As the study authors note, further research needs to be done using the actual vitamin D status of patients hospitalized with COVID-19.

So, it seems, perhaps we jumped the gun on saying vitamin D supplements can protect against COVID-19. But we do know people that don’t have a vitamin D deficiency do better against respiratory infections, so it does seem reasonable to think it may be useful against COVID-19 – another respiratory infection. We just don’t have enough evidence to recommend it.

Who is At Risk for Vitamin D Deficiency?

The populations most at risk for vitamin D deficiency are those whose sun exposure is limited or who have malabsorptive conditions. Some specific groups are:

• Breastfed infants
• Older adults
• Homebound individuals, and those with occupations that limit sun exposure
• People with dark skin
• People with inflammatory bowel disease, and other similar conditions
• People who are obese or who have had gastric bypass surgery

What are the Vitamin D Recommendations?

While we may not be recommending vitamin D supplementation for the treatment or prevention of COVID-19 just yet, it is still important to make sure you get enough of the vitamin daily to prevent a deficiency, and stay in optimal health.

The RDA (Recommended Dietary Allowance) for vitamin D, for men and women, age 19-70 is 600 IU per day. For men and women over 70 years old, the RDA is 800 IU per day (1).

Where Can I Get Vitamin D?

Many people meet at least some of their vitamin D requirements through sunlight exposure. There are many factors that can impact how much vitamin D the skin is able to make using sunlight, including, cloud cover, sunscreen use, latitude, and whether you are in the shade or direct sunlight. It is generally thought that 5-30 minutes of sun exposure, between the hours of 10AM and 3PM at least twice a week, without sunscreen, is adequate for vitamin D levels (1). However, because of skin cancer concerns, it is also important to limit sun exposure, and use sunscreen and other coverings when in the sun.

Some foods are a natural source of vitamin D, while others are fortified with it. Below is a partial list of these foods. For a full list, visit the USDA National Nutrient Database for Standard Reference.

• Cod liver oil, 1 Tbsp – 1360 IUs
• Farmed Rainbow Trout, 3 oz – 645 IUs
• Sockeye Salmon, 3 oz – 570 IUs
• Milk, Vitamin D Fortified (any milkfat), 1 cup – 120 IUs
• Milk Substitutes, Vitamin D Fortified (soy, almond, or oat), 1 cup – 100-144 IUs
• Ready to eat Cereal, fortified with vitamin D, 1 serving – 80 IUs
• Egg yolk, 1 large – 44 IUs
• Tuna, canned in water, 3 oz – 40 IUs
• Cheese, 1 oz – 12 IUs

Sometimes mushrooms contain a substantial amount of vitamin D, but they must have been exposed to ultraviolet light. It will specify on the label if this is the case.

Supplements may be used to reach the RDAs in the event it is not possible to through diet. Always talk to your doctor before beginning any supplement. Look for vitamin D3, as it is closest to the form the body can absorb. Do not take more than recommended, as vitamin D can build up in the body and become toxic. Too much vitamin D can lead to anorexia, heart arrhythmias, and increased calcium in the blood which can cause damage to the heart, blood vessels, and kidneys.

As always, if you are concerned about getting enough vitamin D, or think you may have a deficiency, talk with your doctor. A simple blood test can show if you aren’t getting enough vitamin D, and your doctor can help you decide the best course of action for you.