Life Extension Magazine®

Microscope used to study vitamin D effects on viral infections

Vitamin D’s Winter Immune Benefits

Clinical trials show that vitamin D decreases rates and severity of viral respiratory tract infections. More than 70% of Americans have either deficient or insufficient vitamin D blood levels.

Scientifically reviewed by: Julia Dosik, MPH, in August 2023. Written by: Julie Myers.

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

A meta-analysis of randomized, controlled clinical trials showed a protective effect against acute respiratory infections with vitamin D supplementation.9

More than 40% of Americans have been found to have insufficient blood levels of vitamin D (defined as levels between 20-30 ng/mL).

An additional nearly 30% of Americans have lower vitamin D levels (below 20 ng/mL) that qualify as deficiency.10

This factor may be especially important among adults aged 60 and over.10

Life Extension® supporters have long been advised of the importance of maintaining an optimal vitamin D level between 50-80 ng/mL.

Oral intake of vitamin D to ensure healthy levels may help protect against winter-season conditions.

Impact on Immune Function

Lungs vulnerable to viruses

For the body to produce its own vitamin D, we need direct skin exposure to sunlight.

But we spend most of our time indoors or covered up by clothes and sunscreen. And 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.

What you need to know

Vitamin D’s Immune Benefits

  • Vitamin D supports the immune system’s response to illnesses of all kinds.
  • More than 40% of Americans have insufficient blood levels of vitamin D.
  • Past studies show 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, such as the flu, are more common during winter.

One of the reasons for this may be seasonal variations in our vitamin D levels. During winter, we get less sun, leading to lower vitamin D production.11,12 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.12,13

Low vitamin D is also a risk factor for more severe lung disease and a hyperinflammatory response to infection.14,15,16

Vitamin D’s Protective Actions

Woman wearing mask while running

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

Maintaining adequate levels of vitamin D:14,17-20

  • 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.

Oral Vitamin D Reduces Risk

Many studies have evaluated whether daily oral intake of vitamin D can reduce rates of viral respiratory illness.

Meta-analyses of clinical trials have shown that vitamin D has a protective effect against respiratory tract infections.9,21

The impact of vitamin D treatment is greatest in those who, to begin with, have low levels of vitamin D.9

Life Extension® supporters have long been advised of the importance of maintaining an optimal vitamin D level between 50-80 ng/mL, and yearly blood testing.


Vitamin D supports the immune system in many different ways, helping to shield the respiratory tract from viral illness.

A large majority of adults have vitamin D levels below the optimal level.

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

If you have any questions on the scientific content of this article, please call a Life Extension® Wellness Specialist at 1-866-864-3027.

Blood Testing Vitamin D Levels

Tech testing blood vials

There are no universal guidelines for frequency of vitamin D testing. However, given the high prevalence of vitamin D deficiency and the strong association of low vitamin D levels with several health issues, annual testing and supplementation to achieve adequate blood levels is highly recommended.

Annual blood tests can let people know whether they are taking the correct dosage to ensure optimal blood levels of vitamin D.

If you do not already maintain an optimal blood level of 25-hydroxyvitamin D of 50 to 80 ng/mL, then take between 5,000 to 8,000 IU of vitamin D daily with meals.


  1. Bennett AL, Lavie CJ. Vitamin D Metabolism and the Implications for Atherosclerosis. Adv Exp Med Biol. 2017;996:185-92.
  2. Gaksch M, Jorde R, Grimnes G, et al. Vitamin D and mortality: Individual participant data meta-analysis of standardized 25-hydroxyvitamin D in 26916 individuals from a European consortium. PLoS One. 2017;12(2):e0170791.
  3. Grubler MR, Marz W, Pilz S, et al. Vitamin-D concentrations, cardiovascular risk and events - a review of epidemiological evidence. Rev Endocr Metab Disord. 2017 Jun;18(2):259-72.
  4. Ingraham BA, Bragdon B, Nohe A. Molecular basis of the potential of vitamin D to prevent cancer. Curr Med Res Opin. 2008 Jan;24(1):139-49.
  5. Meehan M, Penckofer S. The Role of Vitamin D in the Aging Adult. J Aging Gerontol. 2014 Dec;2(2):60-71.
  6. Toffanello ED, Coin A, Perissinotto E, et al. Vitamin D deficiency predicts cognitive decline in older men and women: The Pro.V.A. Study. Neurology. 2014 Dec 9;83(24):2292-8.
  7. Aranow C. Vitamin D and the immune system. J Investig Med. 2011 Aug;59(6):881-6.
  8. Baeke F, Takiishi T, Korf H, et al. Vitamin D: modulator of the immune system. Curr Opin Pharmacol. 2010 Aug;10(4):482-96.
  9. Martineau AR, Jolliffe DA, Hooper RL, et al. Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. BMJ. 2017 Feb 15;356:i6583.
  10. Liu X, Baylin A, Levy PD. Vitamin D deficiency and insufficiency among US adults: prevalence, predictors and clinical implications. Br J Nutr. 2018 Apr;119(8):928-36.
  11. Ginde AA, Mansbach JM, Camargo CA, Jr. Association between serum 25-hydroxyvitamin D level and upper respiratory tract infection in the Third National Health and Nutrition Examination Survey. Arch Intern Med. 2009 Feb 23;169(4):384-90.
  12. Cannell JJ, Vieth R, Umhau JC, et al. Epidemic influenza and vitamin D. Epidemiol Infect. 2006 Dec;134(6):1129-40.
  13. Berry DJ, Hesketh K, Power C, et al. Vitamin D status has a linear association with seasonal infections and lung function in British adults. Br J Nutr. 2011 Nov;106(9):1433-40.
  14. Dancer RC, Parekh D, Lax S, et al. Vitamin D deficiency contributes directly to the acute respiratory distress syndrome (ARDS). Thorax. 2015 Jul;70(7):617-24.
  15. Parekh D, Thickett DR, Turner AM. Vitamin D deficiency and acute lung injury. Inflamm Allergy Drug Targets. 2013 Aug;12(4):253-61.
  16. Youssef DA, Miller CW, El-Abbassi AM, et al. Antimicrobial implications of vitamin D. Dermatoendocrinol. 2011 Oct;3(4):220-9.
  17. Teymoori-Rad M, Shokri F, Salimi V, et al. The interplay between vitamin D and viral infections. Rev Med Virol. 2019 Mar;29(2):e2032.
  18. Telcian AG, Zdrenghea MT, Edwards MR, et al. Vitamin D increases the antiviral activity of bronchial epithelial cells in vitro. Antiviral Res. 2017 Jan;137:93-101.
  19. Zdrenghea MT, Makrinioti H, Bagacean C, et al. Vitamin D modulation of innate immune responses to respiratory viral infections. Rev Med Virol. 2017 Jan;27(1).
  20. Tsujino I, Ushikoshi-Nakayama R, Yamazaki T, et al. Pulmonary activation of vitamin D3 and preventive effect against interstitial pneumonia. J Clin Biochem Nutr. 2019 Nov;65(3):245-51.
  21. Bergman P, Lindh AU, Bjorkhem-Bergman L, et al. Vitamin D and Respiratory Tract Infections: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. PLoS One. 2013;8(6):e65835.