How Does Vitamin D Support Our Immune System?

Ingredient Spotlight 22 November 2020

Vitamin D doesn’t just help with growth and bone strength – a number of studies have shown that  a regular intake of Vitamin D supplements significantly reduces the risk of catching a cold, flu or other respiratory infections. 

Some background history 

Before the discovery of antibiotics, in particular Streptomycine – the antibiotic used against Bacillus and Tuberculosis – those suffering from this unpleasant illness were sent off for Heliotherapy by the sea or in the mountains. 

Throughout the treatment, individuals benefitted from exposure to “good air”, but most importantly to the sun. 

The beneficial effects of Vitamin D on the immune system were most likely discovered by empirical manner, given that this vitamin was only identified during the 1920s. 

Findings confirmed by Meta-analysis 

In medical jargon, meta-analysis is bibliographic research which collects, reuses and compares several existing studies carried out in previous years. 

The meta-analysis of BMJ which appeared in 2017 compared results from 25 clinical trials with a total of 11,000 participants. 

This meta-analysis was able to demonstrate several interesting elements: 

  • Individuals with lower Vitamin D levels in their blood are also more vulnerable to winter illnesses. 
  • Inversely, an supplemented intake of Vitamin D appears beneficial in preventing viral and bacterial infections. 


Small, daily doses for maximum effectiveness 

According to BMJ’s study, Vitamin D provides greater prevention against winter illnesses when taken daily, with Vitamin D intake reducing the risk of respiratory illnesses by 20%. 

Whilst the initial blood test showed a lack of Vitamin D, a supplemented intake of Vitamin D could further reduce this risk by 70%!

On the contrary, the effects were less evident amongst those taking Vitamin D in concentrated amounts every month or every three months – for example as treatment for osteoporosis. 


Results shown amongst the elderly

Amongst the elderly, an increased Vitamin D intake could reduce the risk of respiratory infections, such as pneumonia, by up to 40%! 

According to Professor Adit Ginde, professor of medicine at Colorado University’s School of Medicine, “Vitamin D can improve the immune system’s ability to tackle infections as it boosts the first line of defence”. In effect, the elderly, especially those in retirement homes, tend to be more vulnerable to pneumonia, bronchitis and flu due to a weaker immune system. 

According to the those conducting this study, therapeutic treatments against respiratory illness are limited and antibiotics have no effect against viral infections. Vitamin D however appears to be the solution – “a discovery which could save lives!” according to the quite enthusiastic Professor Ginde! 

as well as in the hospital.. 

According to Professor Bernard Salle, Professor Emeritus of Paediatrics at the Claude-Bernard University in Lyon and member of the French National Academy of Medicine, a sufficient level of Vitamin D could help to avoid the often costly complications of winter flu amongst the elderly. 

Similarly, the 50,000 or so cases of nosocomialinfections(those contracted in hospitals) could also be avoided, with these costing around 2.4 to 6 billion euros and causing around 4,200 deaths every year! 

Zoom on vitamin D: How does it really work? 

Vitamin D acts in two ways on our immune system: 

  • It inhibits adapted/acquired immunity at the origin of allergies 
  • It boosts innate immunity, our first line of defence against bacteria, viruses and encourages the mutation of monocytes into macrophages. 


When in contact with infectious pathogens such as Bacillus or Tuberculosis, monocytes and macrophages, with sufficient Vitamin D concentration, will then produce ‘natural antibiotics’. 


In practice

Systematic analysis show that a significant percentage of the population are lacking in Vitamin D. This is in part due to few foods containing enough Vitamin D and also due to less and less exposure to sunlight. 

A regular intake of natural sources of Vitamin D in small doses should therefore also play an important part in strengthening our immune system. 



  • High-Dose Monthly Vitamin D for Prevention of Acute Respiratory Infection in Older Long-Term Care Residents: A Randomized Clinical Trial- Journal of the American Geriatrics Society Volume 65, Issue 3, Pages C1–C1, 455–666, e56–e76
  • Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data BMJ 2017;356:i6583