L-Ascorbic acid and D-isoascorbic acid in a common cold survey.

In a survey of double-bind design, 3 groups of approximately 70 student volunteers took 1 g L-ascorbic acid, 1 g D-isoascorbic acid, or placebo tablets every day for 15 weeks and the incidence and duration of colds were recorded. The group taking D-isoascrobic acid suffered 34% fewer colds than the other two groups; the results were also analyzed in relation to the sex and smoking habits of the volunteers. The rationale for investigating D-isoascorbic acid, an isomer of L-ascorbic acid which has limited antiscorbutic activity, is discussed.