Can some food additives or nutrients affect symptoms? The jury is still out.
Diet alone probably isn't the driving force behind the multiple behavioral and cognitive symptoms that plague children with attention deficit hyperactivity disorder (ADHD). But several studies have renewed interest in whether certain foods and additives might affect particular symptoms in a subset of children with ADHD.
All of the qualifiers in the previous sentence are intentional. Traditional research finds no support for radical diets like the Feingold diet — which eliminates nearly all processed foods as well as many fruits and vegetables — for the majority of children with ADHD. And there is no easy way to identify the few children who might benefit from diets that prohibit particular foods.
Yet parents — and some researchers — wonder if more modest dietary changes could supplement standard multimodal treatment that includes behavioral therapy and other evidence-based psychotherapies, school support, medication, and parent education. Here's a brief review of the evidence on the dietary interventions that have received the most mainstream attention.
Artificial colorings and additives
Since the 1970s, researchers have investigated whether the synthetic dyes, flavors, and preservatives found in many commercially prepared and "junk" foods might contribute to hyperactivity or other symptoms of ADHD. Many of the studies are small or flawed, and there is no consensus about how such additives might contribute to ADHD symptoms in children.
Interest in the topic of additives has been reignited by a well-designed study in Britain, not least because its results convinced the United Kingdom's Food Standards Agency (roughly equivalent to the FDA) to urge food manufacturers to remove six artificial coloring agents from food marketed to children in Britain.
The researchers designed a randomized, double-blind, placebo-controlled study to test the effects of the preservative sodium benzoate and six artificial food colorings on hyperactivity in 153 preschoolers (who were 3 years old) and 144 elementary students (who were 8 or 9 years old). The researchers intentionally conducted the study in a community sample of healthy children, rather than restricting it to those diagnosed with ADHD. But they did ask teachers to fill out a questionnaire to assess hyperactivity for the children at the start of the study, to provide some baseline measures.
For six weeks, the children consumed foods and drinks free of sodium benzoate and the six coloring agents. At weeks 2, 4, and 6, the children consumed plain juice (placebo) or juice containing one of two additive mixes every day for a week.
Mix A contained the preservative plus the colorings sunset yellow, carmoisine, tartrazine, and ponceau 4R; mix B contained the preservative plus sunset yellow, carmoisine, quinoline yellow, and allura red AC.
The drinks had the same flavor and color from one week to the next, but contained different amounts of the added mix. For the older children, the daily amount of additives in mix A equaled the amount of food coloring found in two bags of candy, while the daily amount in mix B was equivalent to four bags of candy.
The researchers asked parents and teachers to assess the children's behavior using standard clinical instruments, and also asked independent reviewers to observe the children at school. The older children were also assessed with the Conners' Continuous Performance Test II, which uses visual cues to assess attention and hyperactivity.
The investigators found a mild but significant increase in hyperactivity in both age groups of children — across the board, regardless of baseline hyperactivity levels — during the weeks when they consumed drinks containing artificial colors. This replicated findings of an earlier study they did in 3-year-old children. Using a complex calculation of "effect size," the investigators estimated that the additives might explain about 10% of the behavioral difference between a child with ADHD and one without the disorder.
This was similar to the effect size reported in an earlier meta-analysis conducted by researchers at Columbia University and Harvard University. Their analysis of 15 trials evaluating the impact of artificial food coloring suggests that removing these agents from the diets of children with ADHD would be about one-third to one-half as effective as treatment with methylphenidate (Ritalin).
But like the authors of the British study, the authors of the meta-analysis cautioned that only a minority of children are particularly vulnerable to the effects of artificial additives. They also pointed out that determining which children are susceptible is difficult, though not impossible. Although some experts have recommended testing children with ADHD for food reactions, there is no test for additives.
Parents could try eliminating the major sources of artificial colors and additives — candy, junk food, brightly-colored cereals, fruit drinks, and soda — from their child's diet for a few weeks, to see if symptoms improve. One practical challenge to keep in mind, however, is that studies of sugar elimination have shown that parents may wrongly assume that changes in their child's behavior reflect consumption of a "problem" food.
In one frequently cited study about sugar, researchers recruited 35 mother-and-son pairs. All the mothers believed their sons — then ages 5 to 7 — were sugar-sensitive. The researchers told the mothers their sons would be randomly assigned to an experimental group that received a high dose of sugar or to a control group that received aspartame. In reality, all the boys received aspartame. The mothers who thought their sons ingested a large amount of sugar reported that their child's behavior was significantly more hyperactive afterward. The researchers concluded that parental expectation may color perception when it comes to food-related behaviors.
Omega-3 fatty acids
Essential fatty acids fuel basic cell functioning, improve overall immunity, and enhance heart health. By definition, the body cannot make essential fatty acids, so these nutrients must be consumed in the diet. One group, the omega-3 fatty acids (eicosapentaenoic acid [EPA], docosahexaenoic acid [DHA], and alpha-linolenic acid [ALA]), is obtained from salmon, tuna, and other cold-water fish, as well as from some seeds and oils. The other group, the omega-6 fatty acids (especially linoleic acid), is obtained primarily from vegetable oils.
While a balance of omega-3 fatty acids and omega-6 fatty acids is best for overall health, the typical American diet contains too few omega-3s, often in a one-to-10 ratio or lower with omega-6 fats. Researchers have explored whether a deficiency of omega-3 fats might contribute to symptoms of ADHD because these fatty acids perform a number of functions in the brain, such as affecting transmission of the neurotransmitters dopamine and serotonin and helping brain cells to communicate. ADHD and an omega-3 deficiency also share two symptoms: excess thirst and increased need to urinate. Some evidence suggests that children with ADHD may have low levels of essential fatty acids.
Only a few randomized controlled studies have evaluated omega-3 supplements for children with ADHD. A review by the American Psychiatric Association's Omega-3 Fatty Acids Subcommittee included two placebo-controlled studies that found DHA supplements alone were ineffective at alleviating symptoms of ADHD, and another three that concluded combining omega-3 and omega-6 supplements might help. But because of the way the studies were designed, it was difficult to determine the specific benefit of omega-3 supplements.
Although other studies have been published since the APA review, none have resolved the question of whether omega-3 or omega-6 supplements might help children with ADHD. Several clinical trials are under way and may provide such answers in the future.
In the meantime, the recommendations of the APA subcommittee are a helpful guide: encourage children with ADHD to consume levels of omega-3 fatty acids recommended as part of a healthy diet. For children, that means consuming up to 12 ounces (two average meals) a week of a variety of fish and shellfish that are low in mercury, such as shrimp, canned light tuna, salmon, and pollack, along with daily plant sources of unsaturated fats.
Deficiencies of particular vitamins or minerals — such as zinc, iron, magnesium, and vitamin B6 — have been documented in children with ADHD. But the results of trials testing whether supplementation with vitamins or minerals alleviates ADHD symptoms have been inconsistent.
Although vitamin or mineral supplements may help children diagnosed with particular deficiencies, there is no evidence that they are helpful for all children with ADHD. Furthermore, megadoses of vitamins, which can be toxic, must be avoided.
What's a parent to do?
A diet or dietary supplement that eases the symptoms of ADHD would be a boon for anyone living with this disruptive disorder. So far, though, the evidence provides only limited support for restrictive diets, avoiding preservatives or artificial food colorings, consuming more omega-3 fats, or taking specific vitamins or minerals.
For now, the consensus on a sensible approach to nutrition for children with ADHD is the same recommended for all children: eat a diet that emphasizes fruits and vegetables, whole grains, healthful unsaturated fats, and good sources of protein; go easy on unhealthy saturated and trans fats, rapidly digested carbohydrates, and fast food; and balance healthy eating with plenty of physical activity.
A healthful diet may reduce symptoms of ADHD by reducing exposure to artificial colors and additives and improving intake of omega-3 fats and micronutrients. But it certainly will improve overall health and nutrition, and set the stage for a lifetime of good health.
Freeman MP, et al. "Omega-3 Fatty Acids: Evidence Basis for Treatment and Future Research in Psychiatry," Journal of Clinical Psychiatry (Dec. 2006): Vol. 67, No. 12, pp. 1954–67.
McCann D, et al. "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," Lancet (Nov. 3, 2007): Vol. 370, No. 9598, pp. 1560–67.
Schab DW, et al. "Do Artificial Food Colors Promote Hyperactivity in Children with Hyperactive Syndromes? A Meta-Analysis of Double-Blind Placebo-Controlled Trials," Journal of Developmental and Behavioral Pediatrics (Dec. 2004): Vol. 25, No. 6, pp. 423–34.
Weber W, et al. "Complementary and Alternative Medical Therapies for Attention-Deficit/Hyperactivity Disorder and Autism," Pediatric Clinics of North America (Dec. 2007): Vol. 54, No. 6: pp. 983–1006.
Another perspective on diet and ADHD, from Attention
Magazine (published by CHADD):
For more references, please see www.health.harvard.edu/mentalextra.