Vitamin C and the Common Cold: A Second MZ Cotwin Control Study

Abstract

Self-reported cold data have been analyzed for 95 pairs of identical twins aged 14-64 who took part in a double-blind trial of vitamin C tablets. One member of each twin pair took a tablet containing 1 g vitamin C and the other took a well-matched placebo each day for 100 days. In the total sample there was no effect of vitamin C in preventing colds. However, subdivision of the data showed a significant preventive effect of the placebo in the 51 pairs living together and an equal and opposite preventive effect of the vitamin C in the 44 pairs living apart. The placebo effect in the pairs living together may be attributed to the large proportion who wrongly perceived which treatment they were taking. The reduction of colds in the vitamin C group of the pairs living apart was about 20%. There were significant correlations between cold symptoms reported and the personality trait of neuroticism. No side effects or substantive changes in serum biochemistry could be attributed to the vitamin C dose.

Vitamin C supplementation and common cold symptoms: factors affecting the magnitude of the benefit

“…The previous searches were extended by MEDLINE searches to identify newer vitamin C-common cold trials. All placebo-controlled studies using regular vitamin C supplementation with 1 g/day of the vitamin were selected for the present quantitative analysis (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31), and the results are shown in Table 1. Regular supplementation refers here to initiating supplementation with healthy people and continuing over the occurring common cold episodes.…”

“…All studies except one (14) were double-blind. Some of the placebo groups were given 10-70mg/day of vitamin C to ensure that the effects of the larger dose were not due to the alleviation of a true dietary deficiency (25,26,28,30). The Relative Effect on the severity of common cold episodes in the vitamin C groups relative to the placebo groups was calculated for each study as the difference between the outcomes in the vitamin C and placebo group divided by the outcome in the placebo group (Table 1).…”

Development and modification of child food preferences and eating patterns: behavior genetics strategies

“…Useful discussions on the power of the cotwin control design are provided by Carr and colleagues. [7][8][9] 'High-risk' designs Another strategy used in the literature has been to compare the eating traits of children of obese parents vs nonobese parents. Parental obesity status, especially maternal weight, is a strong risk factor for childhood obesity.…”

“…Articles discussing the power of the cotwin control design can be found elsewhere. [7][8][9] The cotwin control design has been used to address other issues in adult obesity and weight control 10,11 Discordant Sibling Designs What environmental or other variables distinguish siblings that differ in eating patterns or obesity status?…”

Does Vitamin C Alleviate the Symptoms of the Common Cold? - A Review of Current Evidence

“…All studies except 1 (6) were double-blind. Some of the placebo groups were given 10-70 mg/day of vitamin C to ensure that the effects of the larger doses were not due to alleviation of dietary deficiency (17,19,21). The group of twins living together in the study by Carr et al (19) has not been included, for reasons previously discussed (25).…”