Lack of effect on mental efficiency of extra vitamin C

Twenty men (mean age 21 yr) took part in a double-blind cross-over trial to compare psychomotor performance when plasma vitamin C levels were high (16.28 +/- 3.75 mg/l) owing to supplementation, with times when levels were low (6.15 +/- 3.88 mg/l). Subjects were tested at 0730, 1130, and 1900 h by an hour-long auditory vigilance test to assess alertness, a digit-symbol substitution task to test short-term memory, and a memory-for-digits test to measure immediate memory. No significant differences were found on these measures of performance, nor was there any change in their subjectively rated sheep quality, alertness, concentration, or mood.