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Phytochemicals are compounds in plant-derived foods that have biological activity in the body. Phytochemicals naturally occur in vegetables and fruit. In broad terms, they can be said to be any chemical or nutrient derived from a plant source. However, in common usage, they have a more limited definition. They are usually used to refer to compounds found in plants that are not required for normal functioning of the body but that nonetheless have a beneficial effect on health or an active role in the amelioration of disease.[/b]
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Many phytochemicals are thought to be destroyed or removed by modern food processing techniques, possibly including cooking. For this reason, it is believed that industrially processed foods are less beneficial (contain fewer phytochemicals) than unprocessed foods. The absence or deficiency of phytochemicals is believed to have contributed to the increased prevalence of the above-cited preventable or treatable causes of death in contemporary society.[/b]
There's also another interesting article I found on this decent neuroscience blog
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The study looked at 14 trials that tested the cognitive benefits of taking vitamin B6, B12, and folic acid. Unfortunately, on most tests of mental function, no improvement was seen. [Reference below]
Now this is not to say vitamins can’t boost brain power. The question, however, becomes: Where are you getting them from? The majority of recent research indicates you have to go to the raw food source as opposed to a pill.[/b]
So I think most of the improvements seen from vitamin pills are at least partially placebo effect. It would be interesting to find a raw vegetable or fruit with a high concentration of B vitamins and eat it flat-out raw every day for a few weeks or something and see what happens.