Evidence has shown that both C-reactive protein (CRP) and serum amyloid component A (SAA) are increased in individuals with gastritis and stomach cancer. Controlling the level of these biomarkers by inhibiting the gastric infection with high doses of ascorbic acid may reduce the risk of carcinogenesis. A population-based double-blind randomised controlled trial in a Japanese population with atrophic gastritis in an area of high stomach cancer incidence was conducted between 1995 and 2000. Daily doses of 50 or 500 mg vitamin C were given, and 120 and 124 participants completed the 5-year study, respectively. Although serum ascorbic acid was higher in the high-dosage group (1·73 (sd 0·46) μg/l) than in the low-dosage group (1·49 (sd 0·29) μg/l, P< 0·001), at the end of the study, no significant difference was observed for CRP between the low- and high-dosage groups (0·39 (95 % CI 0·04, 4·19) mg/l and 0·38 (95 % CI 0·03, 4·31) mg/l, respectively; P= 0·63) or for SAA between the low- and high-dosage groups (3·94 (95 % CI 1·04, 14·84) μg/ml and 3·85 (95 % CI 0·99, 14·92) μg/ml, respectively; P= 0·61). Vitamin C supplementation may not have a strong effect on reducing infections in individuals with atrophic gastritis.