evidence: A meta-analysis of findings from 25 randomized controlled trials found daily or weekly vitamin D supplementation reduced the risk of acute respiratory infections, and the effect was stronger in those with low baseline vitamin D levels. Daily doses between 800 and 2,000 IU appeared to be most effective. The analysis further showed treatment regimens that included large boluses (30,000 IU vitamin D or more) did not reduce infection risk.184 Nevertheless, a controlled trial in nursing home residents found monthly 100,000 IU boluses of vitamin D, in addition to standard daily doses of 400–1,000 IU, resulted in greater respiratory infection prevention than standard daily dosing alone, but was associated with a higher risk of falling (a known adverse side effect of high-dose vitamin D supplementation).185 [...] Siddiqui M, Manansala JS, Abdulrahman HA, et al. Immune Modulatory Effects of Vitamin D on Viral Infections. Nutrients. Sep 21 2020;12(9)doi:10.3390/nu12092879 [...] Hemilä H. Vitamin C and Infections. Nutrients. Mar 29 2017;9(4)doi:10.3390/nu9040339