Researchers in one study said the central nervous system needs B-complex vitamins in particular to function well. Doctors measured diet, lifestyle, mood and mental performance in 210 healthy men, aged 30 to 55, at the start and end of the study. Each day, the men took a placebo or a supplement containing high-dose B-complex vitamins: 15 mg of B1, 15 mg of B2, 10 mg of B6, 10 mcg of B12, 150 mcg of biotin, 400 mcg of folic acid, 50 mg of nicotinamide, 23 mg of pantothenic acid, plus 500 mg of vitamin C, 100 mg of calcium, 100 mg of magnesium, and 10 mg of zinc. After 33 days, while the placebo group had not changed, the B-vitamin group had improved mental health ratings, felt less stress and more vigor, and tended toward a better mood overall compared to the start of the study. In a 60-minute mental task test, while the placebo group did not change from the start of the study, the B-vitamin group performed with more speed, accuracy and less mental fatigue.