In a preliminary study of women in Italy, iodine deficiency severe enough to cause hypothyroidism during pregnancy was associated with an increased risk of ADHD in their children.¹ Women who are contemplating pregnancy or who are pregnant should get adequate amounts of iodine in their diet and should discuss with their healthcare provider whether iodine supplementation is appropriate.

In a double-blind study, supplementation with L-carnitine for eight weeks resulted in clinical improvement in 54% of a group of boys with ADHD, compared with a 13% response rate in the placebo group.² The amount of L-carnitine used in this study was 100 mg per 2.2 pounds of body weight per day, with a maximum of 4 grams per day. No adverse effects were seen, although one child developed an unpleasant body odor while taking L-carnitine. Researchers have found that this uncommon side effect of L-carnitine can be prevented by supplementing with riboflavin. Although no serious side effects were seen in this study, the safety of long-term L-carnitine supplementation in children has not been well studied. This treatment should, therefore, be monitored by a physician.

Some children with ADHD have lowered levels of magnesium. In a preliminary, controlled trial, children with ADHD and low magnesium status were given 200 mg of magnesium per day for six months.³ Compared with 25 other magnesium-deficient ADHD children, those given magnesium supplementation had a significant decrease in hyperactive behavior.

In a double-blind study, children with ADHD who received 15 mg of zinc per day for six weeks showed significantly greater behavioral improvement, compared with children who received a placebo.⁶ This study was conducted in Iran, and zinc deficiency has been found to be quite common in certain parts of that country. It is not clear, therefore, to what extent the results of this study apply to children living in other countries.

A deficiency of several essential fatty acids has been observed in some children with ADHD compared with unaffected children.^7,8 One study gave children with ADHD evening primrose oil supplements in an attempt to correct the problem.⁹ Although a degree of benefit was seen, results were not pronounced. In a 12-week double-blind study, children with ADHD were given either a placebo or a fatty-acid supplement providing daily: 186 mg of eicosapentaenoic acid (EPA), 480 mg of docosahexaenoic acid (DHA), 96 mg of gamma-linolenic acid (GLA), 864 mg of linoleic acid, and 42 mg of arachidonic acid. Compared with the placebo, the fatty-acid supplement produced significant improvements in both cognitive function and behavioral problems.¹⁰ No adverse effects were seen. In a preliminary trial, supplementation with approximately 400 mg of flaxseed oil and 25 mg of vitamin C, each twice a day for three months, was associated with an improvement of symptoms in children with ADHD.¹¹

A deficiency of several essential fatty acids has been observed in some children with ADHD compared with unaffected children.^12,13 One study gave children with ADHD evening primrose oil supplements in an attempt to correct the problem.¹⁴ Although a degree of benefit was seen, results were not pronounced. In a 12-week double-blind study, children with ADHD were given either a placebo or a fatty-acid supplement providing daily: 186 mg of eicosapentaenoic acid (EPA), 480 mg of docosahexaenoic acid (DHA), 96 mg of gamma-linolenic acid (GLA), 864 mg of linoleic acid, and 42 mg of arachidonic acid. Compared with the placebo, the fatty-acid supplement produced significant improvements in both cognitive function and behavioral problems.¹⁵ No adverse effects were seen. In a preliminary trial, supplementation with approximately 400 mg of flaxseed oil and 25 mg of vitamin C, each twice a day for three months, was associated with an improvement of symptoms in children with ADHD.¹⁶

Though it has not been studied, theoretically shelled hemp seed may be useful for people with ADHD due to its content of essential fatty acids.^22,23

B vitamins, particularly vitamin B6, have also been used for ADHD. Deficient levels of vitamin B6 have been detected in some ADHD patients.²⁴ In a study of six children with low blood levels of the neurotransmitter (chemical messenger) serotonin, vitamin B6 supplementation (15–30 mg per 2.2 pounds of body weight per day) was found to be more effective than methylphenidate (Ritalin®). However, lower amounts of vitamin B6 were not beneficial.²⁵ The effective amount of vitamin B6 in this study was extremely large and could potentially cause nerve damage, although none occurred in this study. A practitioner knowledgeable in nutrition must be consulted when using high amounts of vitamin B6. High amounts of other B vitamins have shown mixed results in relieving ADHD symptoms.^26,27

B vitamins, particularly vitamin B6, have also been used for ADHD. Deficient levels of vitamin B6 have been detected in some ADHD patients.²⁸ In a study of six children with low blood levels of the neurotransmitter (chemical messenger) serotonin, vitamin B6 supplementation (15–30 mg per 2.2 pounds of body weight per day) was found to be more effective than methylphenidate (Ritalin®). However, lower amounts of vitamin B6 were not beneficial.²⁹ The effective amount of vitamin B6 in this study was extremely large and could potentially cause nerve damage, although none occurred in this study. A practitioner knowledgeable in nutrition must be consulted when using high amounts of vitamin B6. High amounts of other B vitamins have shown mixed results in relieving ADHD symptoms.^30,31