Vitamin D & Flu Prevention
Vitamin D has been recommended as a way to boost the immune system. We summarize the key studies behind Vitamin D & the Flu below. There is strong evidence linking Vitamin D to protection against the flu and other respiratory tract infections.
Professionally Reviewed by Charles Li, MD

Vitamin D May Protect Against The Flu

A study found that students were just over half as likely to get Influenza A if they were given vitamin D supplements compared to students who received a placebo. This study was conducted in Japan and was designed to investigate whether Vitamin D supplements could reduce the incidence of the flu among schoolchildren. Only Influenza A was studied.

Why this matters

The flu is one of the most devastating diseases and one of the leading causes of death from an infectious disease. Vitamin D deficiency is also a very common condition. This study suggests that vitamin D supplements, which are very cheap and easy to buy, may help reduce your odds of getting the flu.

From the study

"In conclusion, our study suggests that vitamin D3 supplementation during the winter season may reduce the incidence of influenza A. This effect was prominent in specific subgroups of schoolchildren. Moreover, asthma attacks were also prevented by vitamin D3 supplementation. "

Source: Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren

Vitamin D May Prevent Respiratory Tract Infections

Why this matters

Generally, nutrition research tends to have conflicting answers. Even experts disagree. This particular study provides strong evidence that Vitamin D may indeed help with preventing respiratory tract infections. These include COVID-19 and the flu.

Study Source:

"Vitamin D supplementation was safe and it protected against acute respiratory tract infection overall. Patients who were very vitamin D deficient and those not receiving bolus doses experienced the most benefit."

Source: Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data

Our Take

Vitamin D & the Flu

Vitamin D & The Flu

There is strong evidence linking Vitamin D to protection against the flu and other respiratory tract infections. Given that Vitamin D tends to be cheap, safe, and easy to find, it may be a good idea to talk to your doctor about whether starting Vitamin D supplements may be a good idea, particularly if you don't get enough direct sunlight.


Vitamin D
what is it?
where to get it
Vitamin D
what is it?
Key Facts
  • type
    fat soluble
  • source
    diet, skin
  • other names
    calciferol, cholecalciferol
Use List

bone growth



Vitamin D
where to get it
the sun

your body can create vitamin D with assistance from the sun


some foods such as milk and fish contain vitamin D


Vitamin D can also be obtained from dietary supplements

Key facts: Vitamin D plays a key role in bone growth, calcium absorption, and your immune system. Unlike some vitamins, your body can produce it with the help of the sun. Sunlight helps catalyze a key reaction in the production of Vitamin D.

Chart of how vitamin D is made

How Vitamin D is Made: Skin cells are believed to create 7-Dehydrocholesterol. UVB Rays from the sun convert this to Vitamin D3. Your liver and kidneys convert this to active Vitamin D. Vitamin D is then distributed throughout the body.

More Information on Vitamin D

On Vitamin D Deficiency

"Vitamin D is produced by skin exposed to ultraviolet B radiation or obtained from dietary sources, including supplements. Persons commonly at risk for vitamin D deficiency include those with inadequate sun exposure, limited oral intake, or impaired intestinal absorption. Vitamin D adequacy is best determined by measurement of the 25-hydroxyvitamin D concentration in the blood. "

Vitamin D & the Immune System

"Vitamin D can modulate the innate and adaptive immune responses. Deficiency in vitamin D is associated with increased autoimmunity and an increased susceptibility to infection. As immune cells in autoimmune diseases are responsive to the ameliorative effects of vitamin D, the beneficial effects of supplementing vitamin D-deficient individuals with autoimmune disease may extend beyond the effects on bone and calcium homeostasis."