Should you be taking a vitamin D supplement right now?

Vitamin D isn’t just good for your bones, it can help strengthen your immune system too. Here’s how to get enough of this key nutrient.
 Even with some sunshine and a healthy diet that includes vitamin D-rich foods, a supplement is likely necessary.
Even with some sunshine and a healthy diet that includes vitamin D-rich foods, a supplement is likely necessary.Getty Images

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By Samantha Cassetty, RD

Vitamin D may be best known for the role it plays in helping to build and maintain healthy bones, but since the coronavirus crisis started, many people have been wondering which nutrients are involved in supporting the immune system — and vitamin D happens to be one such nutrient. While the current evidence doesn’t support claims that any particular vitamin (or other nutrient or supplement) can help prevent, treat or cure COVID-19, vitamin D plays an important role in how your immune system functions, and notably, in its fight against viruses. Here’s why you need to pay attention to vitamin D, along with tips to make sure you’re getting enough of this key nutrient.

What is vitamin D and what does it do?

In its active form in your body, vitamin D is a hormone that’s deeply involved in your health. Without sufficient vitamin D, bones may become brittle and weak, and ultimately susceptible to fractures, particularly in postmenopausal women. Though it isn’t definitive, research suggests that vitamin D may help protect against type 2 diabetes. And there’s evidence that a vitamin D deficiency may contribute to the development of autoimmune conditions, like rheumatoid arthritis.

What is most top-of-mind for many right now is how Vitamin D is involved in enabling you to mount a healthy defense against immune system invaders, like viruses. Studies have suggested that people with low levels of this nutrient are more likely to catch upper respiratory infections, like colds and flus. A recent analysis concluded that people taking a daily vitamin D supplement are more likely to stay infection-free. This benefit was even more pronounced among those who had extremely low vitamin D levels to begin with.

According to Bruce Hollis, Ph.D., a professor of pediatrics, biochemistry and molecular biology and the director of pediatric nutritional sciences at the Medical University of South Carolina, vitamin D is one of the most potent immune-regulating hormones. When your body senses a viral intruder, your immune cells release cells called cytokines. Some of these cells cause an inflammatory process and when your immune system is operating well, this process is slowed down by the release of other cytokine cells.

In people with severe illness from COVID-19, however, one of the factors that leads to death is a cytokine storm — a type of response in which the body’s immune system goes haywire because the inflammatory cells are operating in overdrive. “Vitamin D acts to bring this action under control,” says Hollis. While we can’t say that vitamin D can prevent COVID-19, a new report in the journal, Nutrients, suggests that there’s enough evidence to warrant making sure your vitamin D level is in a healthy range, especially if you’re at risk for serious infection from coronavirus.

Who’s at risk for low vitamin D?

The NIH suggests that there are a number of people who are at risk for low vitamin D levels. Among them are people who get limited exposure to sunlight, which is a large portion of the population on lockdown. Older adults, individuals with dark skin and people with bigger bodies (whether overweight or obese) may be more likely to have low vitamin D levels. People with celiac disease, Crohn’s disease and ulcerative colitis are also at greater risk. Where you live matters too. If you live in northern areas that get fewer days of sunlight, you’re more likely to have a vitamin D deficiency.

Finding out if your vitamin D levels are low involves a simple blood test. While it’s ideal to get tested, Hollis says he assumes that everyone who walks through his door is vitamin D deficient. If you’re not currently taking supplements, it’s a pretty safe bet your levels are low, he says.

Sources of vitamin D?

It’s always a good idea to think about food before supplements, but the reality is that vitamin D is hard to come by in foods. It’s found naturally in oily fish, like salmon and to a lesser extent, sardines, as well as in certain mushrooms and egg yolks. It’s also in select fortified foods, such as milk and certain fortified yogurt, orange juice and cereals.

Like its nickname, “the sunshine vitamin,” suggests, you can also score some vitamin D from spending time in the sun. When exposed to sunlight, your skin activates to manufacture vitamin D. However, this process varies depending on the time of day, amount of cloud or smog cover and whether your body is covered in clothing — or sunscreen. Any of these factors will hinder the conversion process, which means you’ll make less vitamin D. And unexposed sun time isn’t even advised since it raises your risk of skin cancer.

Should you take a vitamin D supplement?

While most experts agree that you can’t reach optimal vitamin D status with food and sunlight alone, it’s still a good idea to eat two servings of seafood a week — a recommendation from our country’s latest Dietary Guidelines that helps ensure you get a range of healthful nutrients, in addition to some vitamin D. If you’re choosing a plant-based milk alternative, make sure it’s fortified with vitamin D. The amount varies from brand to brand (some aren’t fortified at all), so it’s be sure to check. Since shopping for groceries is stressful enough these days, look at labels as you’re unpacking your groceries and if your usual plant-based milk isn’t fortified, try another brand the next time you shop.

Even with some sunshine and a healthy diet that includes vitamin D-rich foods, a supplement is likely necessary. Guidelines published in 2018 in The Journal of Steroid Biochemistry and Molecular Biology suggest supplements are needed to reach healthy blood concentrations. How much vitamin D is recommended? In 2011, the Endocrine Society released guidelines recommending 1,500-2,000 IUs to maintain a vitamin D status above 30 ng/mL. However, Hollis says that his research group and other researchers worldwide target 40-60 ng/mL as the optimal blood level. “To reach that level, adults need 4,000-6,000 IUs of vitamin D3 per day,” says Hollis. “This should be a lifetime supplementation and not only in times of medical peril.” Since the Institutes of Medicine sets the upper limit at 4,000 IUs daily, you may want to schedule a virtual visit with your MD before going above that.