Vitamin D and the Immune System

2 min read

woman sitting in a sunny field

By Markita Lewis, MS, RD

Maintaining a healthy immune system to protect against illness is a top priority for many of us. If you’re not able to spend much time outdoors in the sun, you may be missing out on an essential vitamin that can help strengthen your immune system.

Vitamin D functions both as a vitamin and a hormone within the body. It is turned into cholecalciferol (Vitamin D3) when the skin is exposed to UVB light from the sun. Unfortunately, many factors limit how well we are able to create Vitamin D naturally, and this puts us at risk for deficiency.

According to data collected from the 2011-2012 National Health and Nutrition Examination Survey (NHANES 2011-2012), nearly 40% of adults in the United States over age 20have a Vitamin D deficiency. Certain population subgroups are more likely to have a deficiency — including individuals with darker skin tones, older adults, those with existing health conditions and current or former smokers.

Vitamin D and Immunity Benefits

Research supports the role of Vitamin D in promoting immunity by reducing inflammation, maintaining gut integrity and supporting a healthy microbiome. 

A meta-analysis of clinical trials published in the British Journal of Medicine in 2017 examined the relationship between Vitamin D supplementation and acute respiratory tract infections. Data was analyzed from the 25 clinical trials including a total of 11,321 participants of all ages up to 95. Overall, supplementation of Vitamin D2 or D3 was effective in reducing the risk of acute respiratory tract infections among participants. Daily or weekly doses of Vitamin D provided greater protective effects when compared with onetime large doses. Researchers also found that the protective effects were greater in those who had low levels of Vitamin D at the beginning of the study.

How to Get Enough Vitamin D

So now that you know about the immunity-supporting benefits of Vitamin D, how much should you get daily? According to the Institute of Medicine, adults between the ages of 18 and 70 should get 600 international units (IU) of Vitamin D daily; if you’re over age 70, you need 800 IU daily. You may need more if you are deficient in this vitamin.

Getting enough Vitamin D naturally may be difficult if you are spending more time indoors than usual, so there are alternate sources available. Foods that have Vitamin D include fatty fish, egg yolks, mushrooms exposed to UV light, and some Vitamin D-fortified foods including milk. Taking a Vitamin D supplement or multivitamin containing Vitamin D can also be helpful in meeting daily recommendations.

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