Vitamin D’s winter immune benefits

Life Extension vital mature woman with short gray hair, smiling with a cup in her hand outside on a cold sunny day

Clinical trials show that vitamin D decreases rates and severity of viral respiratory tract infections. 53% of Europeans have shown either deficient or insufficient vitamin D blood levels.

Vitamin D has shown promise against winter illness because it plays a critical role in supporting the immune system. Low vitamin D levels have been associated with higher rates of many chronic diseases. (1-6) This includes an increased risk for acute communicable diseases, including viral infections in vitamin D deficient people. (7,8) 

Reports indicate that 40% of the population in Europe has been shown to have insufficient blood levels of vitamin D (estimates of the prevalence of 20 ng/mL). It has also been reported that 13% of Europeans have severe deficiency (defined as 12 ng/ml). (9)

Oral intake of vitamin D to ensure healthy levels may help protect against winter-season conditions. A meta-analysis of randomized, controlled clinical trials showed a protective effect against acute respiratory tract infections with vitamin D supplementation. (10,11) 

Vitamin D's impact on immune function

For the body to produce its own vitamin D it needs direct skin exposure to sun. But we spend most of our time indoors or covered up by clothes and sunscreen. Spending more time in the sun raises the risk of skin cancer and accelerated skin aging.

The other way to get vitamin D is through diet, but most foods contain only modest amounts. As a result, a majority of people are getting too little of this crucial vitamin.

Having low levels of vitamin D is associated with a greater risk for many health problems, from cognitive decline to heart disease. (1-6)

Vitamin D supports immune health by helping: (7,8)

  • Optimize immune function that protects us from infectious disease.
  • Control overly aggressive inflammatory immune responses, which can inflict systemic damage.

Benefits of vitamin D:

  • Vitamin D supports the immune system’s response to illnesses of all kinds.
  • Studies show that more than 40% of people have insufficient blood levels of vitamin D.
  • Other studies indicate that low levels of vitamin D are associated with increased rates and severity of viral infections.
  • Clinical trials have shown that vitamin D has a protective effect against respiratory tract infections.

Vitamin D and viral illness

Viral respiratory tract infections, like the flu, are more common during colder months. One of the reasons for this may be seasonal variations in our vitamin D levels. During winter, we get less sun, which in return is leading to lower vitamin D production. (12,13) 

That puts us at increased risk for viral infection. Research shows that infections are more common and more severe in those with vitamin D deficiency. (13,14) Low vitamin D is also a risk factor for more severe lung disease, including acute respiratory distress syndrome (ARDS). (15,16) 

Research suggests that those with insufficient vitamin D are at increased risk of a cytokine storm. (17) This hyperproduction of inflammatory factors leads to worsening disease severity and increased risk of death. Low vitamin D levels may be associated with the dangerous inflammation that occurs in ARDS. (15,16)

Vitamin D’s protective actions

Vitamin D contributes to many functions that help shield the body from infections and lessen their severity. 

Maintaining adequate levels of vitamin D: (15,18-21)

  • Interferes with the ability of viruses to replicate and produce more viruses,
  • Helps support and repair healthy cellular linings in the body, including in the airways of the lungs,
  • Increases production of proteins that shield against bacteria and viruses, enhancing the ability of cells to protect themselves from infection,
  • Improves the ability of immune cells to mount an effective attack against specific viruses, and
  • Helps prevent the immune system from going overboard and producing excessive pro-inflammatory compounds in the lungs.


Vitamin D supports the immune system in many different ways, it also helps shield the respiratory tract from viral illness. A large majority of adults have low levels of vitamin D. 

Studies have shown that oral vitamin D intake modestly decreases rates of viral respiratory tract infections.

Scientifically reviewed by: Julia Dosik, MPH, on October 2020. Written By Julie Myers.


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