Comparison 1. Vitamin D versus placebo (all studies).

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Rate ratio, exacerbations requiring systemic corticosteroids	3	680	Rate Ratio (Random, 95% CI)	0.64 [0.46, 0.90]
2 Time to first exacerbation requiring systemic corticosteroids	2	658	Hazard Ratio (Random, 95% CI)	0.69 [0.48, 1.00]
3 People with one or more exacerbations requiring systemic corticosteroids	7	933	Odds Ratio (Random, 95% CI)	0.74 [0.49, 1.10]
4 People with one or more exacerbations requiring systemic corticosteroids (risk difference)	7	933	Risk Difference (M‐H, Random, 95% CI)	‐0.01 [‐0.04, 0.02]
5 People with one or more exacerbations requiring ED visit or hospitalisation or both	7	963	Odds Ratio (Random, 95% CI)	0.39 [0.19, 0.78]
6 ACT/C‐ACT score	3	713	Mean Difference (Random, 95% CI)	‐0.08 [‐0.70, 0.54]
7 People with fatal asthma exacerbation	7	963	Risk Difference (M‐H, Random, 95% CI)	0.0 [‐0.01, 0.01]
8 FEV1, % predicted	4	387	Mean Difference (Random, 95% CI)	0.48 [‐0.93, 1.89]
9 People with one or more serious adverse event due to any cause	5	879	Odds Ratio (M‐H, Random, 95% CI)	1.01 [0.54, 1.89]
10 People with one or more exacerbation as defined in primary trials	7	999	Odds Ratio (Random, 95% CI)	0.53 [0.28, 0.99]
11 % eosinophils, lower airway	3	525	Mean Difference (Random, 95% CI)	‐0.38 [‐1.92, 1.15]
12 Peak expiratory flow rate	2	302	Mean Difference (Random, 95% CI)	3.16 [‐13.40, 19.72]
13 People with one or more adverse reactions attributed to vitamin D	5	879	Risk Difference (M‐H, Random, 95% CI)	0.0 [‐0.01, 0.01]
14 People withdrawing from trial	9	1093	Odds Ratio (M‐H, Random, 95% CI)	1.07 [0.73, 1.58]