(We already saw that too much iodine could poison both adults and children, and of course too little does not help much - iodine would seem to follow a U-curve like most supplements.) The listed doses at iherb.com often are ridiculously large: 10-50mg! These are doses that seems to actually be dangerous for long-term consumption, and I believe these are doses that are designed to completely suffocate the thyroid gland and prevent it from absorbing any more iodine - which is useful as a short-term radioactive fallout prophylactic, but quite useless from a supplementation standpoint. Fortunately, there are available doses at Fitzgerald 2012’s exact dose, which is roughly the daily RDA: 0.15mg. Even the contrarian materials seem to focus on a modest doubling or tripling of the existing RDA, so the range seems relatively narrow. I’m fairly confident I won’t overshoot if I go with 0.15-1mg, so let’s call this 90%.
Recently I spoke on the phone with Barbara Sahakian, a clinical neuropsychologist at Cambridge University and the co-author of a 2007 article in Nature entitled "Professor's Little Helper". Sahakian, who also consults for several pharmaceutical companies, and her co-author, Sharon Morein-Zamir, reported that a number of their colleagues were using prescription drugs like Adderall and Provigil. Because the drugs are easy to buy online, they wrote, it would be difficult to stop their spread: "The drive for self-enhancement of cognition is likely to be as strong if not stronger than in the realms of 'enhancement' of beauty and sexual function." (In places like Cambridge, at least.)
Vitamin C has long been thought to have the power to increase mental agility, and some research suggests that a deficiency may be a risk factor for age-related brain degeneration including dementia and Alzheimer's.  Furthermore, interesting studies demonstrate that vitamin C may be useful in managing anxiety and stress. One of the best sources of this vital vitamin are blackcurrants. Others include red peppers, citrus fruits such as oranges and broccoli.
Wild salmon. Deep-water fish, such as salmon, are rich in omega-3 essential fatty acids, which are essential for brain function, says Kulze. Both she and Pratt recommend wild salmon for its "cleanliness" and the fact that it is in plentiful supply. Omega-3s also contain anti-inflammatory substances. Other oily fish that provide the benefits of omega-3s are sardines and herring, says Kulze; she recommends a 4-ounce serving, two to three times a week.
Systematic reviews and meta-analyses of clinical human research using low doses of certain central nervous system stimulants found enhanced cognition in healthy people.[21][22][23] In particular, the classes of stimulants that demonstrate cognition-enhancing effects in humans act as direct agonists or indirect agonists of dopamine receptor D1, adrenoceptor A2, or both types of receptor in the prefrontal cortex.[21][22][24][25] Relatively high doses of stimulants cause cognitive deficits.[24][25]