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Archived Comments for: Efficacy of a Carrageenan nasal spray in patients with common cold: a randomized controlled trial

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  1. Vitamin C tablets and zinc acetate lozenges are effective against the common cold

    Harri Hemila, Univ Helsinki

    5 November 2014

    Ludvig et al. write in their background section that vitamins and zinc are not effective against the common cold when systematically reviewed [1]. 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 [2]. 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%)[2]. Ludwig et al. specifically refer to the Karlowski et al. study that was published in 1975 [3]. Karlowski found that 6 g/day of vitamin C was twice as effective as 3 g/day, indicating dose dependency in the high dose region [3-5].

    A systematic review on zinc lozenges found 13 controlled trials [6]. There is 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%) [6].


    1. Ludwig et al. Efficacy of a Carrageenan nasal spray in patients with common cold: a randomized controlled trial. Respir Res 2013;14:124.

    2. Hemilä H, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev. 2013;CD000980.

    3. Karlowski TR, et al. Ascorbic acid for the common cold. A prophylactic and therapeutic trial. JAMA 1975;231:1038-42.

    4. Hemilä H. Vitamin C, the placebo effect, and the common cold: a case study of how preconceptions influence the analysis of results. J Clin Epidemiol 1996;49:1079-1084

    5. Hemilä H. Vitamin C supplementation and common cold symptoms: factors affecting the magnitude of the benefit. Med Hypotheses 1999;52:171-178

    6. Hemilä H. Zinc lozenges may shorten the duration of colds: a systematic review. Open Respir Med J 2011;5:51-58



    Competing interests

    No competing interests