A recent review showed considerable evidence that both influenza epidemics and colds could be related to low seasonal levels of vitamin D. These diseases usually occur in winter when Dermal synthesis of vitamin D through the sun’s UV rays is diminished by reduced exposure to sunlight. This generates vitamin D deficiencies, which in turn has been seen to decrease levels of antimicrobial peptides (AMP) such as cathelicidin, with important immunological functions against viruses and bacteria.
A subsequent randomized controlled study supported this theory, showing that doses of 800 IU daily of vitamin D for one year virtually eliminated the incidence of colds and flu.
Therefore, the use of 800 IU daily of vitamin D can be an effective, economical and safe way to avoid respiratory viral infections, especially in the elderly and with little exposure to sunlight.
Reference: Aloia J, Li-Ng M. Re: epidemic influenza and vitamin D. Epidemiol. Infect 2007; 135: 1095-1096