Vitamin C metabolism and the common cold

Summary Male and female university students at the commencement of common cold symptoms were given a single dose of 500 mg of vitamin C. Plasma and leucocyte ascorbic acid concentrations were then measured for six hours. Symptom severity was recorded. The test was repeated twenty-three days after the last symptom had disappeared. The ascorbic acid blood response curve had then returned to normal. Significant and similar elevations of plasma ascorbic acid occurred in both sexes in the cold and post-cold tests. The leucocyte response was significantly reduced in the males but was unaffected in the females in the cold test. The regression coefficients between leucocyte and plasma values (P/L regressions) confirmed that ascorbic acid metabolism was less deranged in females than males during the cold test. Administration of ascorbic acid was associated with increases in blood ascorbic acid concentrations during the post-cold period but not during colds. A single dose of 1000 mg raised blood ascorbic acid concentrations in both sexes during their colds. The elevation was higher, and maintained for two hours longer in the females.In vitro incubation of leucocytes in ascorbic acid confirmed that their ascorbic acid load could be increased by approximately 100% while cold symptoms were present. A significant association between cold symptoms and the state of ascorbic acid metabolism was demonstrated by correlating the ratio of toxic to catarrhal symptoms with P/L regressions during colds. When catarrhal symptoms are severe, ascorbic acid passes from the leucocytes into the plasma, and thence into the inflamed respiratory membranes. When toxic symptoms are relatively more severe, ascorbic acid is retained in the cells. The beneficial effect of vitamin C on the common cold is associated with its influence on ascorbic acid metabolism. A sex-linked difference in ascorbic acid metabolism is manifested during the common cold which affects assessment of the effects of vitamin C on the common cold.