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Vitamin D for Immune Health

Updated: May 23, 2022

Vitamin D is a fat soluble vitamin that behaves like a hormone. Vitamin D helps your body to absorb calcium, influence cell growth, and reduce inflammation. Vitamin D is well known for its bone health benefits, but it also has a critical role in the immune response. Vitamin D can modulate the innate and adaptive immune responses. Deficiency in vitamin D is associated with increased autoimmunity as well as increased susceptibility to infection.

Strong sunlight initiates vitamin D production in the skin. The liver and kidneys complete the conversion to vitamin D’s most active form, vitamin D3. Most people do not produce enough vitamin D, because their skin is unable to absorb it, they don’t spend enough time outside, or geographically they don’t receive enough sunlight.

There are some food sources of vitamin D, including halibut, tuna, and fortified juice, however it is very hard to get enough vitamin D from food alone. Many Americans are vitamin D deficient.

Evidence has now been accumulating that adequate vitamin D levels may lower a person’s risk of COVID-19. One study of nearly 8,300 adults found that those who took vitamin D supplements were 34% less likely to develop COVID-19 compared to those who did not take vitamin D. Another study found that COVID-19 patients who had higher vitamin D levels were 20 times less likely to have a critical outcome versus a mild one. Another study found that among patients with COVID-19, 99% of those with vitamin D deficiency died.

A recent data analysis from a population-based study measuring long-term vitamin D status in more than 400 million people worldwide, as well as seven clinical studies measuring vitamin D levels post-infection showed that people who had vitamin D levels of 50 nanogram per milliter (ng/ml) or higher preceding SARS-CoV-2 infection were extremely unlikely to die from their illness. The Endocrine Society defines vitamin D deficiency as less than 20 ng/ml, insufficiency as 21-29 ng/ml, sufficiency as 30 ng/ml or higher, with 40-60ng/ml as optimal.

Talk to your doctor about getting your vitamin D blood levels checked and supplementing to keep your level in an optimum range for immune health.

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