Table 1.

Characteristics of included studies in the comparison of vitamin C versus placebo.

Author	Participants		Patients		Episodes of illness		Formulation	Dosing schedule	Outcome
	VC	P	VC	P	VC	P
Anderson [29] 1974	275	293	209	218	417	430	tablet	4g on the first day of illness	episodes of illness, duration, confined to house, off work
	305		231		483			8g on the first day of illness
	277	285	212	233	436	437	tablet	1 g/d vitamin C and 4 g/d at onset of illness on the 1st day only
Anderson [30] 1972	407	411	302	335	561	609	tablet	regular dose of 1g each day and increase to 4g each day for the first three days of any illness	episodes of illness, duration, confined to house
Anderson [31] 1975	150	146	Not reported	Not reported	Not reported	Not reported	tablet	500mg each week, 1500mg on the 1st day and 1000mg daily on days 2 through 5 during an illness	episodes of illness, duration, confined to house, off work, symptoms present
	152				Not reported		capsule
Audera [32] 2001	47	42	47	42	Not reported	Not reported	tablet	1g/d at onset of illness for 3 days	duration, symptoms present
	50		50		Not reported		tablet	3g/d at onset of illness for 3 days
Elwood [33] 1977	1082		32	33	Not reported	Not reported	tablet	3 tablets (3g) per day at onset of illness until the 10 tablets had been taken	duration
			39	25	Not reported	Not reported	tablet
Tyrrell [34] 1977	724	777	225	257	⩾274	⩾329	tablet	4g/d for 2.5 days at onset of illness	duration, off work, symptoms present, in bed
Lewis [35] 1975	43	46	Not reported	Not reported	56	65	capsule	3g/d at onset of illness	episodes of illness, duration, side effect
	57		Not reported		76		capsule	regular dose of 3g each day and increase to 6g each day at onset of illness
Karlowski [36] 1975	Not reported	Not reported	43	46	56	65	capsule	3g/d at onset of illness for 5 days	episodes of illness, duration, symptoms present
	Not reported		57		76		capsule	regular dose of 3g each day and increase to 6g each day at onset of illness
Cowan [37] 1950	77	76	77	76	213	207	tablet	0.67 g of vitamin C every 4 hours at onset of illness, with a maximum of 10 doses	duration, severity