Table 1.

Description of the included trials

Trial [ref.]	N	Setting	Vitamin C		Length of mechanical ventilation (hours)				RoM
			Route	Dose (g/day)	Vitamin C		Control
					Mean	SD	Mean	SD
Bjordahl et al. [11]	185	Cardiac	po	2	28.8	19.2	33.6	24.0	0.86
Amini et al. [12]	137	Cardiac	po	3	7.3	6.0	6.7	4.3	1.10
Dehghani et al .[13]	100	Cardiac	po	1	13.4	2.0	15.4	14.3	0.87
Habib et al. [14]	100	Sepsis	iv	6	110	50	189	72	0.58
Safaei et al. [15]	58	Cardiac	iv	2	15.1	5.39	22.9	20.46	0.66
Ebade et al. [16]	40	Cardiac	iv	3	2.04	0.35	1.99	0.31	1.02
Tanaka et al. [17]	37	Burns	iv	90*	290	211	511	374	0.57
Zabet et al. [18]	28	Sepsis	iv	6*	36.6	16.1	46.8	10.1	0.78
Sadeghpour et al. [19]**	290	Cardiac	po	1	11.8	3.9	14.1	9.5	0.84

The trials are listed by the number of patients (N). The mean age in the trials ranged from 42 to 64 years, with a median of 60 years. The proportion of males varied from 58% to 75%. Five trials were carried out in Iran [12, 13, 15, 18, 19], two in Egypt [14, 16], one in the USA [11], and one in Japan [17]. For detailed descriptions of the trials, see Additional file 1: Table S1. The Amini trial [12] results are modified as described previously [1]

*Estimated vitamin C dose, see the “Methods” section

**Sadeghpour et al. [19] recruited 500 participants but reported the results for just 290 participants [1]. Because of the high dropout rate (42%), we did not include this trial in our calculations, but we overlay the findings in Fig. 4

iv intravenous, po per oral, RoM ratio of means [22]: e.g., for the Bjordahl trial [11], RoM = 0.86, based on 28.8/33.6, and RoM = 0.86 indicates that ventilation time in the vitamin C group was 14% shorter than in the placebo group