Expert Consensus on Brain Health, a statement issued by researchers from the Stanford Center on Longevity and the Max Planck Institute for Human Development, gives a great summary of the science (or lack thereof) behind supplements and programs marketed for brain health. More than 30 experts from Stanford, the Max Planck Institute and other institutions signed the statement.
While there are things that can be done to improve brain health and mental fitness, they say, there's not enough evidence to support the claims of many supplements and programs. Physical exercise and maintaining overall health are important for cognitive fitness. More research is needed to see if various products promoted for brain health are effective.