In a paper published in the British Medical Journal this month, 21 experts from the U.K., Ireland and the U.S. conclude that while vitamin D is “essential for good health” (especially for bones and muscles) and may bolster the immune system, it can also be dangerous in high doses.

“Many people have low blood levels of vitamin D, especially in winter or if confined indoors, because summer sunshine is the main source of vitamin D for most people,” the authors write. “Taking a daily supplement … and eating foods that provide vitamin D is particularly important for those self-isolating with limited exposure to sunlight.” Foods high in vitamin D include fatty fish (such as salmon and tuna), portobello mushrooms, fortified milk and yogurt and eggs.

But high doses of the vitamin — which the authors refer to as “mega doses” can be extremely dangerous.

The paper comes on the heels of a study suggesting that vitamin D deficiency may be linked to higher rates of mortality with COVID-19. But the report warns individuals not to simply start taking those mega doses. “The continued spread of the novel SARS-CoV-2 virus, and the disease COVID-19 that is caused by SARS-CoV-2, has led to calls for widespread high-dose vitamin D supplementation,” the authors write. “These calls are without support from pertinent studies in humans at this time, but rather based on speculations about presumed mechanisms.” 0:02 1:58  New study looks at link between COVID-19 and vitamin D deficiency and the new research revealing a possible link between COVID-19.

The authors note that inundating the body with vitamin D can cause toxicity, and emphasize that there is no proof that doing so prevents the coronavirus. “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,” the report reads. “There are evidenced health risks with excessive vitamin D intakes especially for those with other health issues such as a reduced kidney function.”

Amesh D. Adalja, an infectious disease expert and senior scholar at the Johns Hopkins University Center for Health Security, says that vitamin D deficiency is prevalent in the U.S., especially among black people, but agrees that taking large doses of it blindly can be dangerous. “Vitamin D is a medication, it’s a drug, so it can have side effects,” Adalja says. “When you have acute intoxication you can get a lot of different problems including confusion, vomiting — all kinds of things can happen.”

Vitamin D toxicity — officially referred to by the Mayo Clinic as hypervitaminosis D — is rare, but can cause “a buildup of calcium in your blood (hypercalcemia), which can cause nausea and vomiting, weakness and frequent urination.” The condition can prove most dangerous for those with liver or kidney problems, which Adalja says may lead to a “lower threshold for overdose.”

In an earlier interview on the topic, medical contributor Dr. Kavita Patel said it’s important to be aware of the potential dangers, but adds that overdosing on vitamin D is extremely uncommon. “It’s pretty low-risk, especially if you have normal kidney function,” says Patel. “Vitamin D is not the best for everyone, but if you have normal kidney function then your body should be able to process and clear it through the urine.”

The Mayo Clinic notes that “taking 60,000 international units (IU) of vitamin D a day for several months” has been shown to cause toxicity. But in the U.S., current recommendations are just a fraction of that. The National Institutes of Health’s Office of Dietary Supplements recommends 600 IUs a day of vitamin D for most people, 400 IUs for those under 2 and 800 IUs for those over 70. The BMJ authors write that high doses — up to 10,000 IUs/day — of the nutrient are being recommended online, but the authors “strongly caution against doses higher than the upper limit 4,000 IUs/day.”

And although a major a link between COVID-19 and vitamin D has not been drawn, there is still research that suggests taking the supplement may help with immune function. One large meta-analysis published by Harvard University in 2017, for example, found that taking vitamin D may help prevent serious respiratory infections, such as influenza, especially in those who are deficient in the vitamin.

Dr. Karl Z. Nadolsky Jr., an endocrinologist and clinical assistant professor of medicine at Michigan State University, says that he recommends it for some patients. “I often tell people who seem to be at risk (northern hemispheres, not much sunlight, risk of potential bone disease, etc.) to take 1,000 international units,” Nadolsky says. “This BMJ article cites many appropriate guidances for that and emphasizes to avoid overdosing via keeping under 4,000 international units daily. Doses higher than 1,000 international units should not be necessary for most people with normal absorption.”

Adalja says that those who feel unsure how to proceed should talk to their doctor about getting their vitamin D levels tested. “You want to avoid vitamin D deficiency but you don’t want to overdose on vitamin D,” says Adalja. He adds, like the BMJ authors, that on top of supplements and vitamin D-rich foods, sunlight can be extremely beneficial. “Sunlight is important because it helps synthesize the active form of vitamin D in your body,” says Adalja. “So sun exposure does help with keeping your vitamin D levels higher.”

Medical reference: Yahoolife