Douglas R M, Chalker E B, Treacy B
National Centre for Epidemiology and Population Health, The Australian National University, Canberra, ACT, Australia, 0200.
Cochrane Database Syst Rev. 2000(2):CD000980. doi: 10.1002/14651858.CD000980.
The role of oral ascorbic acid (vitamin C) in the prevention and treatment of colds remains controversial despite many controlled trials. There have also been a number of efforts to synthesize and/or overview the results of these trials, and controversy over what these overviews tell us.
The objective of this review was to answer the following two questions: (1) Does regular high dosage supplementation with vitamin C reduce the incidence of colds? (2) Does taking vitamin C in high doses at the onset of a cold have a therapeutic effect?
This review currently deals only with published trials from two previously published reviews by Kleijnen 1989 and Hemila 1992.
Randomised and non-randomised trials of vitamin C taken to prevent or treat the common cold.
Two reviewers independently extracted data and assessed trial quality.
Thirty trials were included. The quality of the included trials was variable. Vitamin C in doses as high as one gram daily for several winter months, had no consistent beneficial effect on incidence of the common cold. For both preventive and therapeutic trials, there was a consistently beneficial but generally modest therapeutic effect on duration of cold symptoms. This effect was variable, ranging from -0.07% to a 39% reduction in symptom days. The weighted difference across all of the studies revealed a reduction of a little less than half a symptom day per cold episode, representing an 8% to 9% reduction in symptom days. There was no clear indication of the relative benefits of different regimes or vitamin C doses. However in trials that tested vitamin C after cold symptoms occurred, there was some evidence that a large dose produced greater benefits than lower doses.
REVIEWER'S CONCLUSIONS: Long term daily supplementation with vitamin C in large doses daily does not appear to prevent colds. There appears to be a modest benefit in reducing duration of cold symptoms from ingestion of relatively high doses of vitamin C. The relation of dose to therapeutic benefit needs further exploration.
尽管进行了许多对照试验，但口服抗坏血酸（维生素C）在预防和治疗感冒中的作用仍存在争议。也有一些人努力综合和/或概述这些试验的结果，以及关于这些概述能告诉我们什么的争议。
本综述的目的是回答以下两个问题：（1）定期高剂量补充维生素C是否能降低感冒发病率？（2）感冒开始时高剂量服用维生素C是否有治疗效果？
本综述目前仅涉及Kleijnen 1989年和Hemila 1992年之前发表的两篇综述中的已发表试验。
用于预防或治疗普通感冒的维生素C的随机和非随机试验。
两名综述作者独立提取数据并评估试验质量。
纳入了30项试验。纳入试验的质量参差不齐。在几个冬季月份每天服用高达1克的维生素C，对普通感冒的发病率没有一致的有益效果。对于预防和治疗试验，对感冒症状持续时间始终有有益但一般较为适度的治疗效果。这种效果各不相同，症状天数减少幅度从-0.07%到39%不等。所有研究的加权差异显示，每次感冒发作症状天数减少略少于半天，相当于症状天数减少8%至9%。没有明确迹象表明不同方案或维生素C剂量的相对益处。然而，在感冒症状出现后测试维生素C的试验中，有一些证据表明大剂量比小剂量产生的益处更大。
长期每日大剂量补充维生素C似乎不能预防感冒。摄入相对高剂量的维生素C在减少感冒症状持续时间方面似乎有一定益处。剂量与治疗益处的关系需要进一步探索。
