Interest in vitamin D has spiked since the coronavirus outbreak, with many people wondering whether it can help prevent COVID-19 or make the disease less severe if an infection does happen.
A “growing body of circumstantial evidence” links outcomes of COVID-19 and vitamin D status, according to a perspective published last month in The Lancet Diabetes & Endocrinology.
It noted COVID-19 started to spread at the end of winter in the Northern hemisphere when people’s levels of vitamin D in general are at their lowest. Populations that are more likely to have a vitamin D deficiency — including people with darker skin or those living in places where there’s little sunlight — also seemed to be hardest hit by the disease.
Patients with a severe vitamin D deficiency were twice as likely to experience major complications from COVID-19, an analysis of patient data from 10 countries found. The findings were made public last month before peer review.
But while vitamin D is essential for good health, calls for widespread high-dose supplementation to prevent or treat COVID-19 “are without support” from human studies and are based on “speculations about presumed mechanisms,” according to a report published last month in BMJ Nutrition, Prevention & Health.
“There have been some news reports about vitamin D reducing the risk of coronavirus. However, there is no evidence that this is the case,” Britain’s healthcare system, the National Health Service, warned on its website.
What the experts say:
Doctors had mixed opinions.
Vitamin D is important to immunity in general and tamps down inflammation, said Dr. JoAnn Manson, chief of preventive medicine at Brigham and Women's Hospital and professor of medicine at Harvard Medical School in Boston.
An out-of-control inflammatory response, known as a cytokine storm, may be a factor in why some people get so sick from coronavirus.
Still, vitamin D has not been specifically tested for its impact — if any — on coronavirus infections. Manson is hoping to change that with a randomized clinical trial to see if the vitamin can reduce the severity of COVID-19 in people who have recently been diagnosed and lower the risk of infection in their close contacts.
While researchers gather evidence, the pandemic is a good time to be vitamin D aware, she said.
“I’m calling for more attention to avoid vitamin D deficiency,” Manson told TODAY. “This doesn’t mean that everyone should run to be screened for vitamin D deficiency or run out to buy supplement pills.”
Dr. Pieter Cohen, an internal medicine physician who practices at the Cambridge Health Alliance in Cambridge, Massachusetts, said he would strongly discourage people from getting a vitamin D blood test right now.
Before the pandemic, Cohen’s area of expertise was studying dietary supplements; he now works in a COVID-19 outpatient clinic that has cared for more than 2,000 people.
“We don’t recommend vitamin D to our patients and I see no credible evidence that vitamin D has a role in either preventing or treating COVID-19,” Cohen, who is also an associate professor of medicine at Harvard Medical School, said. “We might have evidence in the future that evolves and would change our opinion, but that’s the status here.”
There’s a strong link between obesity and how people cope with the coronavirus — the more they weigh, the worse their outcomes are, he noted. In another link, the more people weigh, the lower their vitamin D level is — though doctors don’t know why, he added.
So it may look like there’s an association between having a low vitamin D level and not doing well with COVID-19, but researchers have to be very careful to not jump to the conclusion that low vitamin D is the cause, Cohen said.
“I would discourage anyone from thinking that any pill is going to resolve this problem. It’s going to be the meticulous social distancing, hand washing, wearing a mask that going to be the key,” he advised.
How to prevent vitamin D deficiency:
It doesn’t take a lot, Manson said. The body can manufacture vitamin D when the skin is exposed to the sun or get it from food.
“I’m not making a general recommendation for supplements. I’m saying: To avoid vitamin D deficiency, it will usually take only being outdoors, getting incidental sun exposure, plus paying attention to the dietary sources of vitamin D,” she noted.
Incidental sun exposure means getting some sunshine during a 30-minute walk or other outdoor exercise while wearing shorts or short sleeves (though you should still use sunscreen). It doesn’t mean going out specifically to sun bathe. Always avoid sunburn, which means avoiding peak sunlight hours in the middle of day, and take steps to prevent skin cancer.
Getting regular exercise outside will also help boost overall health and mood in general, Cohen added.
Dietary sources of vitamin D include fortified dairy products, fortified cereals, fatty fish such as salmon, tuna, and mackerel, and sun dried mushrooms.
For people who are unable to go outside during the pandemic and therefore get zero sunshine, it’s reasonable to take a vitamin D supplement, both experts said. The recommended dietary allowance is 600 international units a day — 800 for people over 70. Supplements tend to come in 1,000 or 2,000 IUs and it would be reasonable to take that amount a day, Manson said.
But avoid “mega dosing,” or ingesting many thousands of IUs a day, because that can be harmful, leading to high blood levels of calcium and other health problems.
“The key point is to avoid vitamin D deficiency and you don’t need to take high doses of supplements for that purpose,” Manson said.