US researchers studied the effects of beta-carotene on cognitive ability in two groups of men.
In 1982, 4,052 men were randomly assigned to take a placebo or beta-carotene, 50mg, every other day.
Between 1998-2001, an additional 1,904 men were randomly assigned to the groups, which were followed until 2003.
Men in the long-term group, but not the short term group, had significantly higher scores for several cognitive tests including verbal memory compared with men who took the placebo.
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