High doses of B vitamins aren’t likely to preserve your memory or thinking ability. Researchers examined 11 large controlled trials that gave a total of 22,000 mostly older people either a placebo or typically high doses of folic acid (400 to 2,500 mcg a day), usually along with vitamins B-6 (3 to 50 mg) and B-12 (20 to 1,000 mcg). After 4 months to 7 years, the B-vitamin takers scored no better on cognitive tests than the placebo takers.
What to do: High doses of B vitamins won’t keep your brain from aging. However, if you are over 50, get the Recommended Dietary Allowance (2.4 mcg a day) of B-12 from a fortified food, like cereal or a supplement