In response to a US National Cancer Institute press release of January 18, 1996, indicating that two beta-carotene trials had shown no benefit but had shown potential harm (Anonymous, 1996), we were obliged to amend the study protocol. Supplementation of beta-carotene was stopped, but the prescription of vitamin C was continued for 5 years. The primary end point was altered from the 10-year cumulative incidence rate of gastric cancer to the 5-year change in serum levels of PGs, Helicobacter pylori infection, oxidative stress markers, and so on. On February 9 and 16, 1996, we invited the participants to community centers, explained in detail the results of the two US studies and the amendment of the study protocol, and collected the discontinued capsules from each participant. Signed consent was obtained again from individuals willing to remain in the study (N=244), and new capsules containing vitamin C only (50 or 500 mg/day) were provided. Although we estimated that a minimum of 1812 participants would be needed for the trial to detect a 40% reduction of the incidence of gastric cancer in the intervention group, the study area was restricted to the village from which participants had already been recruited; no new participants were recruited from the three other municipalities.
Vitamin C was expected to have a preventive or therapeutic effect on the common cold through effects on the immune system. In this report, we aim to evaluate the effect of vitamin C on the incidence, duration, and severity of the common cold.