On 2014 Nov 26, Harri Hemila commented:

Ludwig M, 2013 write in their background section that vitamins and zinc are not effective against the common cold when systematically reviewed. This is not correct.

A systematic review on vitamin C and the common cold showed that vitamin C administration reduced common cold incidence by 52% (95%CI: 36% to 65%) in people who were under short term heavy physical activity Hemilä H, 2013. In addition, regular administration of 1 g/day vitamin C shortened the duration of colds in adults by 8% (95%CI: 3% to 12%) and in children by 18% (95%CI: 9% to 27%) Hemilä H, 2013. Ludwig et al. specifically refer to the Karlowski et al. (1975) study. Karlowski TR, 1975 found that 6 g/day of vitamin C was twice as effective as 3 g/day, indicating dose dependency in the high dose region, see Hemilä H, 1996, Hemilä H, 1999.

A systematic review on zinc lozenges found 13 placebo-controlled trials Hemilä H, 2011. There was substantial heterogeneity between the studies, but the heterogeneity was explained by the dose of zinc and the zinc salt that was used. On the basis of 3 RCT:s, high dose zinc acetate lozenges shortened the duration of colds by 42% (95%CI: 35% to 48%).

There is strong evidence that vitamin C and zinc acetate lozenges have an effect on the common cold.

On 2014 Nov 26, Harri Hemila commented:

Ludwig M, 2013 write in their background section that vitamins and zinc are not effective against the common cold when systematically reviewed. This is not correct.

A systematic review on vitamin C and the common cold showed that vitamin C administration reduced common cold incidence by 52% (95%CI: 36% to 65%) in people who were under short term heavy physical activity Hemilä H, 2013. In addition, regular administration of 1 g/day vitamin C shortened the duration of colds in adults by 8% (95%CI: 3% to 12%) and in children by 18% (95%CI: 9% to 27%) Hemilä H, 2013. Ludwig et al. specifically refer to the Karlowski et al. (1975) study. Karlowski TR, 1975 found that 6 g/day of vitamin C was twice as effective as 3 g/day, indicating dose dependency in the high dose region, see Hemilä H, 1996, Hemilä H, 1999.

A systematic review on zinc lozenges found 13 placebo-controlled trials Hemilä H, 2011. There was substantial heterogeneity between the studies, but the heterogeneity was explained by the dose of zinc and the zinc salt that was used. On the basis of 3 RCT:s, high dose zinc acetate lozenges shortened the duration of colds by 42% (95%CI: 35% to 48%).

There is strong evidence that vitamin C and zinc acetate lozenges have an effect on the common cold.