I think that if people want to be sharp mentally, a lot of the things that promote general wellness also contribute to elevated brain function, like getting plenty of exercise, sleeping well, a balanced diet, drinking plenty of water, taking it easy on the substances, sunlight, and fresh air. The brain is part of the body, and when the body is working better the brain will work better. It's also amazing how much you can learn during a brisk walk around your block, or a jaunt down the bike trail.