When we think of a nutrient to fight colds and flu, most of us would think of vitamin C first. And while this compound is vital and tremendously important for the immune system, the next letter of the alphabet deserves the same respect. Vitamin D is an intrinsic and essential driver for the immune system.
Vitamin D is a pre-hormone that made by the skin that is converted to another form by the liver and then its final form by other cells throughout the body into a steroid hormone.
Vitamin D in all its forms modulates the immune system; it stimulates antimicrobial proteins and killer cells and reduces inflammation. The immune effects of this substance are far-reaching, destroying cancer cells and supporting brain function.
Studies into how vitamin D behaves in the body have led to the knowledge that it can prevent colds, influenza, and other viral infections, especially those that affect the respiratory system.
A 2006 study found that children exposed to sunshine to produce adequate levels of vitamin D were much less susceptible to an outbreak of flu. (1)
A 2010 study supported this finding, with the number of children contracting the flu reduced by half if they took vitamin D supplements in the winter, when flu is more common. An important subset of the study was children with asthma: two children who had taken vitamin D experienced attacks concurrent with the flu whereas twelve children who hadn’t taken vitamin D suffered asthma attacks. (2)
“The Sunshine Vitamin”
Vitamin D has become known as “the sunshine vitamin” because the best place to get it is from sunlight. When sunshine directly touches the skin, a chemical reaction takes place that creates vitamin D3.
This is partially why colds and flu are less common in the spring and summer: because there is more sunshine available for our skin to absorb. Our immune systems are then more robust (thanks to vitamin D) to eradicate invading micro-organisms.
Additionally, flu viruses find it easier to spread in cooler weather when people are more likely to gather indoors than outdoors. (1)
Vitamin D and Colds, Flu, and Respiratory Infections
A large clinical meta-analysis published in The British Medical Journal in 2016 found that vitamin D supplementation (daily and weekly) safely and effectively reduced the risk of respiratory infection by half, including colds and flu.
The improvement of risk was most significant in those with the greatest deficiency in vitamin D at the start of each included study. Regular supplementation was more effective than one dose every now and then. (3)
Compare the efficacy of vitamin D supplementation with that of the annual flu vaccine—it’s much more effective and without the risks that come with vaccination.