Recent research has uncovered a suprising concept that even well-read parents may not realize: IQ and learning can definitely be affected by nutrition, supplements and certain environmental chemicals. That will shock a lot of people, but study after study has showed just this.
And it's not suprising: the brain consumes about 40% of the body's energy. It is metabolic workhouse and needs a constant and abundant supply of nutrients to work optimally.-->
So, all you parents and grandparents out there, please read just how critical this is for the kids in your life:
NEWS FLASH: Please read my link on Fetal Testosterone (and Smoking) if you know anyone trying or about to have kids!
1) Multivitamins. Vitamin supplements given to teens aged 13-16 raised non-verbal IQ scores by an average of 6 points. However, it should be noted that several teens actually improved IQ by over 20 points indicating that nutritional deficiences may have been holding back mental performance. An additional part of the study of the same general age group again showed astonishing results: half of the students increased non-verbal IQ by an amazing 15 points! 
2) B Vitamins and Vitamin C. One study showed a 25% improvement in scores in many categories of cognition and memory among those students with the highest levels of B vitamins and vitamin C as opposed to those with the lowest. 
3) Choline. Choline has produced near miraculous results in animals studies. For example, pregnant rats receiving extra choline produced obviously superior offspring in terms of intelligence and memory.  The researchers wrote that "when rat pups received choline supplements (in utero or during the second week of life), their brain function changed, resulting in the lifelong memory enhancement." Other studies have shown that choline supplementation forms extra dendrites, i.e nerve cell connections. The reason? Choline is a precursor for actylcholine, the memory-building neurotransmitter.
4) DHA. EPA and DHA are the two key omega-3 fatty acids in fish and fish oil, and DHA has now been shown in a study to increase the cognitive development of infants. 
5) No Spanking? I'm not sure what to say about this one, but my job is primarily to report: one 2009 study shows that children who are spanked have a little lower IQ.  You might be thinking, "Well, no one knows if this is causative or if parents with a lower IQ tend to spank". Keep in mind, though, that the researchers of this study tried to control for standard risk factors, including parental education, income, cognitive stimulation and socioeconomic status. So maybe there's something to it? I doubt it, though, because look how friggin' smart I am...
6) Vaccines. Check with your pediatrician regarding your child's vaccines. A good pediatric office buys their vaccines in sets that do not contain the mercury-based preservative Thimerosal. This is important, becacause a 2009 study showed that even one dose of weight-equivalent thimerosal to macaque monkey infants resulted in a brain damage.  Monkeys receiving the thimerosal all had substantial developmental delays. Many studies have shown developmental problems with low levels of methylmercury, which is the "natural form" of mercury found in fish tissue for example.  However, there was little data until this study on the ethyl form of mercury, which was used in thimerosal as an anti-bacterial agent. NOTE: What about the controversial autism-vaccine connection? Mercury allows glutamate to accumulate and some vaccines, especially multiple vaccines, cause the immune system to respond in ways seen in the autistic.  However, multiple studies have shown no connection between vaccinations and autism and so any connection seem weak at best. 
7) Excitotoxins. Surely I don't have to tell anyone to protect their children from excitotoxins?? Just in case, start here with this link on The Dangers of Excitotoxins for more information.
8) CAUTION: Licorice. A recent study showed that women who at large amounts of licorice had children at eight years of age with lower intelligence scores in many key areas. The reason appears to be that licorice has a chemical in it called glycyrrhzin that allows stress hormones to much more easily pass the placental barrier.
9) Exercise. Evidence mounts almost monthly that exercise increases IQ, intelligence, cognition, learning and so on. One recent monster study of 1,000,000 Swedish military males verified previous studies and showed that exercise increases brain power in many ways. The researchers showed that "cardiovascular fitness, but not muscular strength, was associated with cognitive performance on many different measures".  All you parents will be interested to know that the same study showed that cardiovascular exercise from age 15 to 18 was strongly associated with cognition at age 18. In other words, exercising through the high school years actually leads to increased intelligence when the child graduates. Furthermore, the brain development seems to help throughout life: cardiovascular fitness was correlated with future socioeconomic status. And even more direct, one study showed that aerobic capacity was positively associated with mathematics, reading and total academic achievement in third and fifth graders.  (BMI was negatively correlated!)
10) CAUTION - Xenoestrogens: Beware plastics and canned foods around your children, especially boys. Phthlates and Bisphenol-A can be actually modify their developing brain and many researchers believe can actually lead to effeminization. See this link on Bisphenol-A for more details. In addition, a recent study came out that showed the higher the rates of phlthates in the Mom's urine, the less likely their young sons were to play with typical male toys, i.e. they appeared effeminized.  This is, of course, due to the phthlates' laser-like ability to alter testosterone and other androgen hormone levels, which is absolutely critical to the male brain, especially during the developmental years. Many animal studies have validate this and one particularly scary study showed that phthlate exposure was linked to changes in SHBG, testosterone and LH. 
11) Sleep. It's no secret that Sleep Benefits the Brain in many ways, including the refreshing of neurotransmitters and memory mapping for starters. Researchers recently found that it is ultracriticial for the little ones: a study of four year olds by the American Academy of Sleep Medicine found that those with 11 hours or more had the highest math and literacy scores.  Anything less led to lower scores, so put the little guys to bed on time, which leaves you more time for Making Love, Critical for Your Health.
12) Music Training. I discuss at great length the tremendous Health Benefits of Music, but one of the things that I don't discuss is how musical training is a proven brain enhancer. Consider this summary from one set of scientists who stated clearly that "research has also demonstrated that music training in children results in long-term enhancement of visual-spatial, verbal, and mathematical performance." 
13) Air Pollution. Researchers are finding increasing evidence that PAHs (polycyclic aromatic hydrocarbons) are very hard on neurons. This is dangerous news for young children and one recent study found that children exposed in the womb to the highest levels of these PAH's had IQ scores about 4.5 points lower!  Researchers eliminated a lot of the subjectivity by having the mothers wear air quality monitors around their neck. NOTE: It may be that ornamental plants can help. Researcher found that they can dramatically reduce indoor air pollution. See my link on Exercise and Air Pollution for more details. (Solution #2 near the bottom of the page.)
14) Flame Retardants. New research is showing that children's products are packed with nasty flame retardants. "Car seats, changing table pads, sleep positioners, portable crib mattresses, nursing pillows, baby carriers, high chairs and a few other products" have all been found with these chemicals in them.  These are suspected neurotoxins and animal studies show them to be neurologically toxic. 
15) Pesticides. One study has now tied pesticide exposure in the womb to lower IQ scores. The specific chemicals identified were "organophosphate pesticides such as chlorpyrifos, diazinon and malathion." 
16) Overweight. Keep those pounds off your children. Childhood obesity has now been linked to lower math scores. 
ADHD CAUTION: Researchers have long suspected that certain preservatives, food dyes and artificial colors can make some kids ADHD. Of course, ADHD is not directly related to IQ, but let's face it: any child with ADHD is much more easily distracted and that will invariable affect learning and academics. A recent study in the prestigious journal Lancet found that children (ages 3 and 8-9) consuming food colors and additives were significantly more at risk for ADHD, once again proving that you can't just throw a bunch of chemicals into our food supply and expect it to have no effect.  One of the chemicals that is important to note is sodium benzoate, a common preservative added to cokes and other processed foods. For more information, see my link on ADHD.
VOCABULARY SIZE: Do you know what the best predictor of your child's vocabulary level is? Well, the first one is sex: little girls are generally much developed than little boys, owing to testosterone and estrogen levels. However, the second greatest predictor according to one study was parental education level.  The more education the more vocabulary: education isn't just good for you but for your child as well.
1) Personality and Individual Differences, 1991, 12(4):351-362
2) Personality and Individual Differences, 1991, 12(4):363-365
3) JAMA, 1983, 249(21):2917-2921
4) JAMA, 2000, 19(9005):528S-531S
5) Child Development, Sep/Oct 2009, 80(5), "Three Randomized Controlled Trials of Early Long-Chain Polyunsaturated Fatty Acid Supplementation on Means-End Problem Solving in Nine-Month-Olds"
6) J of Aggression, Maltreatment & Trauma, 2009, 18:459-483, 14th International Conference on Violence, Abuse and Trauma, San Diego, Sept. 25, 2009. Murray A. Straus, PhD
7) Neurotoxicology, 2009, "Delayed acquisition of neonatal reflexes in newborn primates receiving a thimerosal-containing Hepatitis B vaccine: influence of gestational age and birthweight", Laura Hewitson, et. al.
9) Degenerative Myelopathy and Excitotoxins - Bad News for Big Dogs, Shawn Messonnier, DVM
10) http://www.medicinenet.com/script/main/art.asp?articlekey=108287, Aberg, M. Proceedings of the National Academy of Sciences, Dec. 8, 2009; 106:20906-20911
12) International Journal of Andrology, 29(1):172-180, Published Online 7 Feb 2006, "Possible impact of phthalates on infant reproductive health"
13) Infant Behavior and Development, 2002, 24:418-424, "Foetal testosterone and vocabulary size in 18 and 24 month old infants"
14) J Sport Exerc Psychol, 2007 Apr, 29(2):239-52, "Physical fitness and academic achievement in third- and fifth-grade students"
15) The Lancet, 3 Nov 2007, 370(9598):1560 - 1567, "Food additives and hyperactive behaviour in 3-year-old and 8/9-year-old children in the community: a randomised, double-blinded, placebo-controlled trial"
17) Ann N Y Acad Sci, Dec 2005, 1060:219-30,"Effects of music training on the child's brain and cognitive development"
18) PEDIATRICS, Aug 2009, 124(2):e195-e202, "Prenatal Airborne Polycyclic Aromatic Hydrocarbon Exposure and Child IQ at Age 5 Years"
21) Science News, "Pesticides tied to lower IQ in children", Janet Raloff May 21st, 2011; Vol.179 #11 (p. 15), http://www.sciencenews.org/view/generic/id/ 73206/title/Pesticides_tied_to_lower_IQ_in_children