Table 1.
Results of vitamin D randomized controlled trials (RCTs) on risk of influenza.
| Country | Population | Baseline 25(OH)D (ng/mL) |
Vitamin D Dose (IU/d) |
Influenza Cases in Vitamin D, Placebo Arms | Outcome |
Ref |
|---|---|---|---|---|---|---|
| Japan | Schoolchildren aged 6–15 yrs |
N/A | 0, 1200 | Type A: 18/167; 31/167. If not taking vitamin D before enrollment: 8/140; 22/140. Type B: 39/167; 28/167 |
Type A: RR = 0.58 (95% CI, 0.34 to 0.99); if not taking vitamin D before enrollment, RR = 0.36 (95% CI, 0.17 to 0.79); no effect for Type B |
[52] |
| Japan | High school students, including many vaccinated against influenza | N/A | 0, 2000 | 20/148; 12/99 | Type A, RR = 1.11 (95% CI, 0.57 to 2.18) | [54] |
| China | Infants, 3–12 mos | 17 | 400, 1200 | Diff. in influenza A viral load, high vs. low vitamin D on day 4 of illness: 1.3 ± 0.5 vs. 4.5 ± 1.4 × 106 copies/mL | [53] | |
| Japan | 223 patients with IBD, mean age 45 yrs |
23–24 | 0, 500 | 8/115; 6/108 |
RR = 1.25 (95% CI, 0.45 to 3.49) | [55] |
| Vietnam | Children aged 3–17 yrs | 26 | 0, 14,000 /wk |
50/650; 43/650 |
HR = 1.18 (95% CI, 0.79 to 1.78) | [56] |
Note: 95% confidence interval (95% CI); day (d); hazard ratio (HR); inflammatory bowel disease (IBD); months (mos); not available (N/A); relative risk (RR); upper respiratory tract infection (URTI); week (wk); years (yrs).