Placebo controlled RCTs: Proportion of participants experiencing at least one acute respiratory infection, overall and stratified by potential effect-modifiers
| Variables | No of trials | Proportion with ≥1 ARI, intervention group (%) | Proportion with ≥1 ARI, control group (%) | Odds ratio (95% CI) | I2% | P for heterogeneity |
|---|---|---|---|---|---|---|
| Overall | 34 | 8307/14155 (58.7) | 8196/13660 (60.0) | 0.89 (0.81 to 0.98) | 40.0 | 0.009 |
| Baseline 25(OH)D, nmol/L | ||||||
| <25 | 19 | 1348/1798 (75.0) | 1388/1819 (76.3) | 0.78 (0.53 to 1.16) | 47.2 | 0.012 |
| 25 – 49.9 | 27 | 3411/4637 (73.6) | 3337/4491 (74.3) | 1.03 (0.91 to 1.17) | 4.1 | 0.40 |
| 50 – 74.9 | 28 | 1607/2761 (58.2) | 1531/2542 (60.2) | 0.90 (0.75 to 1.07) | 14.1 | 0.25 |
| ≥75 | 24 | 923/1520 (60.7) | 895/1458 (61.4) | 0.97 (0.81 to 1.16) | 0.0 | 0.74 |
| Dosing frequency | ||||||
| Daily | 18 | 1056/2134 (49.5) | 1020/1871 (54.5) | 0.75 (0.61 to 0.93) | 52.5 | 0.005 |
| Weekly | 5 | 4357/6288 (69.3) | 4388/6274 (69.9) | 0.97 (0.88 to 1.06) | 0.0 | 0.41 |
| Monthly or less frequently | 11 | 2894/5733 (50.5) | 2788/5515 (50.6) | 1.00 (0.91 to 1.09) | 0.0 | 0.50 |
| Daily dose equivalent, IU[a] | ||||||
| <400 | 2 | 482/1175 (41.0) | 511/1133 (45.1) | 0.65 (0.31 to 1.37) | 86.3 | 0.007 |
| 400–1000 | 10 | 656/1236 (53.1) | 627/1069 (58.7) | 0.70 (0.55 to 0.89) | 31.2 | 0.16 |
| 1001–2000 | 14 | 4693/7885 (59.5) | 4712/7817 (60.3) | 0.96 (0.87 to 1.06) | 8.0 | 0.37 |
| >2000 | 7 | 2291/3462 (66.2) | 2250/3444 (65.3) | 1.05 (0.84 to 1.31) | 37.1 | 0.15 |
| Trial duration, months | ||||||
| ≤12 | 28 | 1852/4754 (39.0) | 1807/4307 (42.0) | 0.82 (0.72 to 0.94) | 39.9 | 0.017 |
| >12 | 6 | 6455/9401 (68.7) | 6389/9353 (68.3) | 1.03 (0.95 to 1.11) | 0.0 | 0.97 |
[a] Data from one trial that included higher-dose, lower-dose and placebo arms18 are excluded from this sub-group analysis, since the higher-dose and lower-dose arms spanned the 1,000 IU/day cut-off, rendering it unclassifiable