Dr. Anthony Fauci does believe in the benefits of vitamin D while he admitted most 'so-called immune-boosting' supplements marketed amid the coronavirus pandemic could do nothing. 

Fauci, director of the National Institute for Allergy and Infectious Diseases, said during an Instagram Live on September 10, "If you are deficient in vitamin D, that does have an impact on your susceptibility to infection. So I would not mind recommending, and I do it myself taking vitamin D supplements."

Determining if you are vitamin D deficient and how much supplement you need to take isn't very easy. For years, medical professionals have been debating the efficacy of routine vitamin D screenings and supplement recommendations.

Fauci Says Take Vitamin D If You’re Deficient. How to know If You Are?
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House Select Subcommittee On Coronavirus Crisis Holds Hearing On Urgent Need For A National Plan WASHINGTON, DC - JULY 31: Dr. Anthony Fauci, director of the National Institute for Allergy and Infectious Diseases, testifies before a House Subcommittee on the Coronavirus Crisis hearing on July 31, 2020 in Washington, DC. Trump administration officials are set to defend the federal government's response to the coronavirus crisis at the hearing hosted by a House panel calling for a national plan to contain the virus.

"You're wandering into a maze," Dr. Clifford Rosen, an endocrinologist and professor of medicine at Tufts University's School of Medicine that studied vitamin D for more than 30 years, told CNBC Make It. coming from the experts, here is the thing you should know about vitamin D:

How to know if you are vitamin D deficient?

Researchers estimated 35% of adults and nearly 50% of infants in the U.S. had vitamin D deficiency, according to the NIH study published in 2014. It can be hard to determine without a blood test. The early signs of vitamin D deficiency are precise if they exist. However, as per the experts, you may not show any symptoms at all.

Vitamin D deficiency could cause accelerated skin aging and dry skin, as per a dermatologist at Northwell Health's Huntington Hospital, Dr. Raman Madan. As the lack of vitamin D goes, it could be severe to result in bone fractures and muscle weakness, says Paul Thomas, scientific consultant and registered dietitian nutritionist at the National Institutes of Health's Office of Dietary Supplement. 

Studies have found that prolonged vitamin d deficiency can cause bone-related diseases in both adults and children. With all those effects of vitamin d deficiency, the only way to know if you are vitamin d deficient is to take a blood test through a licensed doctor, says Thomas. 

But not all medical professionals think that routine testing for vitamin D is a good idea. 

How to get vitamin D without supplements

Natural vitamin D builds up in the blood when a person's intake is sufficient from the sunlight and food, as per Thomas. "If your vitamin D blood level is sufficiently good at the end of the summer, it can remain at adequate levels throughout the winter ... if you get some vitamin D from food." 

According to the NIH, excessive sun exposure might be unhealthy for other reasons. Still, it won't cause vitamin D toxicity as the body naturally limits the amount of vitamin D it produces.

For food, "the only foods naturally containing vitamin D are mushrooms exposed to sunlight, cod liver oil, oily fish like wild-caught salmon that has about 600-1000 IUs vitamin D, and eight ounces of milk or orange fortified with vitamin D contains 100 IUs," says, Dr. Michael Holick, a vitamin D researcher, director of Bone Health Care Clinic, and professor of medicine at Boston University, chaired the expert panel that wrote the NES guidelines.

Getting sensible sun exposure "for some" vitamin D is recommended, but caveats that "you cannot make any significant vitamin D before 10 AM and after 3 PM no matter where you live in the U.S."

Simultaneously, wearing sunscreen with a sun protection factor of 30 would reduce the body's ability to make vitamin D in your skin by 97.5%, Holick says. 

Check these out:

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