grassrootshealth.net/blog/c...
"Using the data you provided for the GrassrootsHealth study, we found that the percent of participants who experienced the flu in the prior 6 months was 55% lower for those with a vitamin D level at or above 40 ng/ml who also reported taking 1,000 mg/day or more of supplemental vitamin C compared to those with a vitamin D level below 40 ng/ml who reported no supplemental vitamin C intake."