It is a logical scientific conclusion that in winter people with depleted vitamin D levels fall ill more often.
Vitamin D activates and boosts the activity of various immune cells123 and it is necessary for the formation of antimicrobial substances (alpha- and beta-defensin) in saliva, tears and sweat.
For example, a 6-month study was performed involving 800 young Finnish males, counting the number of days they missed work due to illness caused by an upper respiratory infection. The men whose level of vitamin D was lower than 16 ng/ml (the recommended norm is at least 30 ng/ml), were ill and missed work significantly more often. Smokers especially need to consider supplementing vitamin D3, as they tend to display significantly lower levels of the vitamin as compared to non-smokers4.
- Peelen E. et al. Effects of vitamin D on the peripheral adaptive immune system: a review. Autoimmun Rev. 2011; 10(12):733-743.
- Prietl B.et al. Vitamin D and immune function. Nutrients. 2013; 5(7):2502-2521.
- Veldman CMet al. Expression of 1,25-dihydroxyvitamin D(3) receptor in the immune system.Arch Biochem Biophys. 2000 Feb 15;374(2):334-8.
- Laaksi I. et al. An association of serum vitamin D concentrations below 40 nmol/L with acute respiratory tract infection in young Finnish men. Am J Clin Nutr. 2007; 86(3):714–717.