En español | You know vitamin D can help you fend off osteoporosis and falls. But if recent headlines have you thinking you might want to pop some more of it to avoid a severe case of COVID-19, know that researchers are still sorting out how, exactly, a deficiency in the vitamin may make you more vulnerable to the disease's more serious symptoms.
For now, experts such as those publishing in a recent BMJ Nutrition, Prevention & Health report don't recommend you boost your intake to avoid COVID-19 complications. As they wrote, “There is no strong scientific evidence to show that very high intakes (i.e., mega supplements) of vitamin D will be beneficial in preventing or treating COVID-19.” What's more, there are risks involved with downing excessive doses of the vitamin — particularly for those with health conditions such as kidney disease.
While researchers continue to research a possible link between COVID-19 and vitamin D levels, here's what we do know about this bone-building (and muscle-strengthening!) nutrient — and how to know if you need a supplement to get the recommended daily allowance.
Crucial for your bones, heart and more
By now, most of us know that vitamin D plays an important role in promoting the absorption of bone-fortifying calcium. But in this case, more is not necessarily more: “If your vitamin D level is sufficient, it doesn't seem like you get a lot of benefit from supplementation,” says Karl Nadolsky, , a clinical endocrinologist and clinical assistant professor of medicine at Michigan State University.
Those of us who are deficient in the vitamin — an oft-cited study puts the number at over 40 percent of the U.S. population — may reap benefits from raising their levels. “We know that having very low levels of vitamin D is bad for a lot of things, especially bones,” Nadolsky says. “It's certainly associated with a lot of things, like type 2 diabetes, cardiovascular health, even early death.” Vitamin D deficiencies have also been linked to breast cancer. Problem is, it's hard to tell if a deficiency of this type is a consequence of ill health, or its cause.
There is some encouraging research that suggests that boosting your level of D and bringing it back to safe levels may improve health outlooks. A recent study published in Seminars in Cancer Biology, for instance, suggests “a good vitamin D status” may be beneficial both in cancer prevention and in the prognosis of several cancers. And organizations such as the National Osteoporosis Foundation consider both vitamin D and calcium to be essential to maintaining dense, strong bones as you age.
And although a clear connection with COVID-19 has not been found, a 2017 study involving more than 11,000 participants found evidence that vitamin D may help protect against upper respiratory tract infections.
Why the sun is still the best source
One of the best ways to get enough vitamin D is through sun exposure, since skin absorbs ultraviolet-B (UVB) rays to manufacture the nutrient. Evidence shows this can happen even if you're wearing sunscreen. “There are a number of studies that show using sunscreen does not prevent the formation of vitamin D,” says Henry Lim, senior vice president of Academic Affairs at the Henry Ford Health System, in Michigan. In a 2019 British Journal of Dermatology study, researchers noted an increase of vitamin D in participants who wore sunscreen during a week of cloudless weather.
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And though most dermatologists recommend applying a shot glass–size amount of sunscreen to your entire body, most of us apply less — in amounts too small to block all of the UVB light, Lin notes. What's more, it takes only a little sun exposure to enable the body to produce our daily quota. Lim suggests 15 to 20 minutes of unprotected sun exposure a day, three days a week, leaving your face and arms bare.
The best way for people who aren't getting that much sun exposure to get enough vitamin D is from supplements. “It's difficult to get enough vitamin D solely from the foods you eat,” says Beth Kitchin, assistant professor of nutrition sciences at the University of Alabama at Birmingham. While fatty fish such as salmon, canned sardines and canned tuna are the best sources — and while foods like milk, orange juice and cereal are often fortified with the vitamin — few people can consume enough of these sources to meet the recommended daily allowance (RDA).
How to supplement wisely
According to the Food and Nutrition Board, people ages 1 to 70 need 600 IU a day; for those over 70 it's 800 IU a day. But, Nadolsky says, “It's a personalized thing. Most people certainly can get away with anywhere from 600 to 1,000 IU a day.”
Generally, it's recommended not to go over 4,000 IU a day, unless you have a malabsorption problem, caused perhaps by a gastric bypass, an inflammatory bowel disease, such as Crohn's disease, or an autoimmune issue, such as celiac disease — all of which may require significantly higher doses than usual to get back to normal.
"People say, ‘I know vitamin D is good for me,’ and take 5,000 IU a day, in addition to a multivitamin, for a long period of time,” says Kitchin. “Those are the folks I'm concerned about. People have a tendency to think more is better, but in some cases, more can be dangerous.”
In fact, you may be overdoing it without even realizing it, since you may be getting vitamin D from several sources, such as multivitamins, calcium supplements, even some joint supplements. To avoid this, Kitchin recommends scanning nutrition labels and doing the math. “It can really add up. You may be getting a good amount of vitamin D without having to take a D supplement!”
Typically, doctors don't order vitamin D as part of a standard blood test. But those who may be at risk for deficiency should consider having their levels tested and possibly monitored. “Some people may be more likely to have levels that slip,” Kitchin explains. “Others may have osteoporosis or a family history of it, so we like to keep an eye on them.” After the numbers come in, your doctor may recommend higher doses or adjust the amount you're downing.