It is the flu season. The CDC reported widespread influenza activity in 41 states last week. Influenza kills about 350,000 people in the world, almost all in the winter. Older adults with chronic illnesses are at the highest risk.
I often get questions about influenza like this one:
Dear Dr. Cannell:
The news this week was all about the “flu spike.” Is it too late to get the flu shot? Is it your recommendation to increase dosage of vitamin D or stay on the usual 5,000 IU/day? What about massive doses if I get the flu, like 50,000 IU/day for several days?
The flu has spiked early this year with more than the expected number of cases for this time of year.
I have always recommended the flu shot, just to cover all possible bases. I also recommend that healthy people keep their vitamin D levels in a natural range, about 50 ng/ml. If one has a chronic illness, I think it wise to keep your 25(OH)D level in the higher range of normal, such as 70-80 ng/ml, although to date no evidence supports such a recommendation.
As far as high daily doses for a few days after getting ill, such as 50,000 IU/day for several days, our group first hypothesized such doses may help treat influenza and we so hypothesized back in 2006. Our reasoning was simple, vitamin D upregulates a naturally occurring anti-microbial peptide, cathelicidin, in humans, antimicrobial peptides that are active against influenza. Recently, scientists discovered that this action of cathelicidin is dose dependent, the more cathelicidin, the more influenza virus killed.
Tripathi S, Tecle T, Verma A, Crouch E, White M, Hartshorn KL. The human cathelicidin LL-37 inhibits influenza A viruses through a mechanism distinct from that of surfactant protein D or defensins. J Gen Virol. 2013 Jan;94(Pt 1):40-9.
We assume, and this has not been proven, the more vitamin D in the blood, the more cathelicidin antibiotic in the immune system. Thus giving “massive” doses for a few days may help. Actually, 50,000 IU/day is not a massive dose; it is a pharmacological dose. If it helps treat influenza, and I suspect it will, then a bottle of 50,000 IU capsules from the only company that makes such a preparation, Bio Tech Pharmacal, is a good drug to keep in your medicine cabinet.
Finally, be careful. While 50,000 IU/day over a few days or a week is fine, it is not a dose to be taken every day for long periods of time, like several months or longer.