It’s possible: Some preliminary research suggests taking a vitamin D supplement may play a role in preventing or managing COVID-19. But not so fast. When it comes to using supplements to protect against respiratory illnesses, the research to date has had mixed results. Yet that doesn’t mean you won’t benefit from adding a vitamin D supplement to your diet or taking a socially distanced walk to soak up the sun, which is a natural source of the essential nutrient. Here’s what you need to know before stocking up on the so-called sunshine vitamin in the context of COVID-19.
Why Are Scientists Talking About Vitamin D to Help Fight COVID-19?
It’s no surprise why scientists are interested in studying vitamin D as a treatment tool for COVID-19, or its deficiency as a potential risk factor for serious illness from the respiratory disease that is caused by the novel coronavirus. After all, vitamin D deficiency is common among many groups at high risk for COVID-19, including the elderly and people with obesity, diabetes, and high blood pressure, says Rose Anne Kenny, chair of medical gerontology at Trinity College in Dublin. Aging and obesity both reduce the ability of the skin to make vitamin D from exposure to the sun’s ultraviolet rays, Kenny says, and obesity specifically is associated with aging and carrying extra weight. Vitamin D is known for aiding several essential body functions that, when compromised, may affect COVID-19 outcomes. “Vitamin D is best known for its effects on bone, but it also has important effects on the immune system,” says Adrian Martineau, PhD, a clinical professor of respiratory infection and immunity at Queen Mary University of London. According to the National Institutes of Health, vitamin D is also important for fighting inflammation and contributing to cell growth. Vitamin D supports the ability of the innate immune system to mount a range of antiviral responses, including production of substances called antimicrobial peptides that are produced by white blood cells and the lining of the lung, Dr. Martineau says. These peptides have antiviral properties as well as antibacterial ones. Vitamin D also dampens potentially harmful inflammatory responses in the body that can be more active in people with health conditions such as obesity and diabetes, which are also risk factors for COVID-19, Martineau adds. RELATED: 7 Ways to Support Your Immune System Naturally
Vitamin D Deficiency May Be Associated With Greater Death Risk From COVID-19
One study, published in May 2020 in the Irish Medical Journal, counterintuitively found that people who live in typically sunny countries in southern Europe, such as Spain and Italy, had higher rates of vitamin D deficiency — and higher COVID-19 infection and death rates — than people in countries including Norway, Finland, and Sweden, which are further north and comparatively less sunny. Kenny says it’s possible people to the north have higher levels of vitamin D because their diets are high in food that has been fortified with vitamin D. Yet this study is circumstantial; it wasn’t a controlled experiment designed to prove whether or how vitamin D levels may directly impact the risk of developing or dying from COVID-19. Researchers also got their data on vitamin D levels and supplementation policies in different countries via previously published papers that used a wide variety of methods to determine what proportion of people had vitamin D deficiency. Also, researchers didn’t examine other micronutrients, including zinc, selenium, and vitamin B6, which may also influence immune function and COVID-19 risk, the study team wrote. RELATED: Can Supplements Protect Me Against the New Coronavirus?
Genetic Predisposition for Higher Vitamin D Levels Doesn’t Affect COVID-19 Risk
But a study published June 2021 in PLoS Medicine looked at the link between vitamin D and COVID-19 from a different angle, and concluded that there may not be a connection between the nutrient and the virus. This study looked for gene variants strongly associated with increased vitamin D levels in 4,134 people with COVID-19 infections and almost 1.3 million uninfected individuals. They wanted to see if people might have a lower risk of becoming infected with the virus or developing severe COVID-19 infections if they had a genetic predisposition for higher vitamin D levels. The study didn’t find any evidence that genetically predicted vitamin D levels influenced whether people got COVID-19 infections. It also didn’t find any evidence that gene variants associated with higher vitamin D levels influenced whether people who did have COVID-19 would be hospitalized or have severe cases. “This (analysis) does not show clear evidence that vitamin D supplementation would have a large effect on COVID-19 outcomes,” says lead study author Guillaume Butler-Laporte, MD, of the department of epidemiology, biostatistics, and occupational health at McGill University in Montreal. One limitation of the study is that it didn’t look at people with vitamin D deficiency, or determine whether these individuals might indeed have a lower risk of developing or dying from COVID-19 infections if they took vitamin D supplements. Another drawback is this genetic analysis only looked at people of European ancestry, and results might be different for other populations.
Vitamin D May Protect Against Respiratory Infections in General
Another study, published in February 2017 in The BMJ, examined data from 25 clinical trials testing the impact of vitamin D supplements on acute respiratory infections, including bronchitis, pneumonia, and sinusitis (a common sinus infection). Combined, these trials involved a total of 11,321 participants who were randomly assigned to take vitamin D supplements or placebo pills and followed for up to 1.5 years. Randomized, controlled trials are the gold standard of medical research because they can show whether an intervention directly causes specific outcomes, a past paper explains. Results from these trials suggested that people who took vitamin D supplements were 12 percent less likely to develop acute respiratory infections than people who didn’t. And among people with the most severe vitamin D deficiency, taking supplements reduced their respiratory infection risk by 70 percent. Yet one limitation of this study is that researchers didn’t have data on whether people received flu shots or if they were diagnosed with chronic obstructive pulmonary disease (COPD), two factors that can independently affect the risk for acute respiratory infections. This study was also done several years before COVID-19 began circling the globe. So although it provides strong evidence that vitamin D supplementation may help with other respiratory infections, it doesn’t prove beyond a doubt that vitamin D will help fight COVID-19. Still, the results do suggest that this is possible given the known functions of vitamin D, says Martineau, who was one of the authors of the BMJ study. RELATED: Your Daily COVID-19 Update
Vitamin D Could Play a Role in Preventing the Flu, Which Is Another Respiratory Illness
Previous studies have had mixed results on the role of vitamin D in preventing the flu, which, though markedly different from COVID-19, as the World Health Organization (WHO) notes, is another severe respiratory illness. A meta-analysis of four studies examining the link between vitamin D supplements and the effectiveness of the flu vaccine, published in March 2018 in Nutrients, didn’t find any connection between the two. One limitation of this analysis is that it’s possible results could vary depending on the quality of the flu vaccine and the strains of influenza in circulation. Previous research may suggest promise, though. One study examined influenza cases among Japanese school children who were randomly assigned to take vitamin D supplements or a placebo. The children who received vitamin D were 42 percent less likely to get the flu. RELATED: 11 Vitamin D Myths and Facts
What Do I Take Away From the Research on Vitamin D and Respiratory Illnesses Like COVID-19?
Larger, more rigorous studies are needed before healthcare professionals recommend vitamin D supplementation for the general public, for COVID-19 prevention or treatment, or otherwise. “There is not enough evidence to say that vitamin D recommendations globally should change on the basis of COVID-19,” says Susan Lanham-New, PhD, head of the nutritional sciences department at the University of Surrey in England. RELATED: Does Vitamin D Deficiency Pose a Special Risk for Black People?
Why You May Still Want to Consider Taking a Vitamin D Supplement
That said, regardless of your risk for COVID-19, some groups may benefit from supplementation. People older than age 60, as well as individuals with chronic health problems, including diabetes, high blood pressure, and lung disease, may benefit from taking a vitamin D supplement, says Paul Marik, MD, chief of pulmonary and critical care medicine at Eastern Virginia Medical School in Norfolk. Daily doses between 1,000 and 4,000 international units (IU) are safe, he adds. People of color, breastfed infants, and people who take certain medications are among the other groups of people at a higher risk for vitamin D deficiency, according to MedlinePlus. Not getting enough direct sunlight is also a risk factor. “Supplementation with vitamin D is particularly important during times of self-isolation associated with limited sunlight exposure,” says Dr. Lanham-New. Wearing sunscreen or clothing that covers most of the skin (whether to prevent skin cancer or premature signs of aging) limits the amount of vitamin D the body can produce from sun exposure, says Matthew Drake, MD, PhD, an associate professor of medicine at the Mayo Clinic in Rochester, Minnesota. And so does sheltering in place to help avoid the spread of COVID-19. “For the majority of people, particularly those unable to spend at least 15 to 30 minutes with direct sun exposure each day, the easiest way to obtain vitamin D is through supplementation with either a multivitamin or with vitamin D directly, both of which can be obtained over the counter and do not require a prescription,” Dr. Drake says. While eating foods high in vitamin D (think: cod liver oil, salmon, trout, and fortified milk) can also help you reach the optimal amount, it isn’t enough, notes the Cleveland Clinic. Exposure to direct sunlight and possibly a supplement can get you there, though. RELATED: Do You Need to Take a Vitamin D Supplement?
How Much Vitamin D Should You Take and Is There an Upper Limit?
For the record, vitamin D recommendations vary widely around the world. Most people should get 600 IU of vitamin D daily, according to the Food and Nutrition Board (FNB) at the Institute of Medicine of the National Academies. For people older than 70 it’s 800 IU, and for infants it’s 400 IU. Because high daily doses of vitamin D can be harmful, don’t exceed standard recommended doses without first checking with your doctor, says Lanham-New. In fact, because everyone’s nutrient needs differ, asking your healthcare team about the right dose for you is smart. You can do that via telemedicine if an in-person visit is less preferable or unavailable. RELATED: 10 Illnesses Linked to Vitamin D Deficiency
Taking Vitamin D During the COVID-19 Pandemic: What’s the Bottom Line?
At this point, it is not clear that vitamin D supplementation will help prevent or treat COVID-19 infection, Drake says. But because vitamin D is safe when taken at reasonable dosages, there is not likely to be any harm for older adults to take recommended amounts of vitamin D, especially if you’re in a high-risk group. “It is now increasingly recognized that vitamin D likely plays a role in immune cell function, such that low vitamin D levels may lead to a reduced ability for each of our immune systems to fight various insults including infections,” says Drake. “Maintaining vitamin D levels within a normal range, therefore, might be one way to improve the immune system’s ability to fight an infection — perhaps such as COVID-19.”
