Diet and ADHD
Last reviewed on October 17, 2012
By Michael Craig Miller, M.D.
Diet is probably not the driving force behind the symptoms of attention deficit hyperactivity disorder (ADHD) inattention, hyperactivity or impulsive behavior. But several studies have stirred interest in the relationship between certain foods or additives and some symptoms of ADHD.
For most children with ADHD, research does not support radical diets, such as those that eliminate nearly all processed foods and many fruits and vegetables. And there is no easy way to identify the few children who might benefit from diets that bar particular foods.
Yet parents and some researchers wonder if more modest dietary changes could be a helpful addition to treatment that now includes psychotherapy, school support, medication and parent education.
Here's a brief review of the evidence for dietary approaches that have received the most attention.
Since the 1970s, researchers have studied whether synthetic dyes, flavors and preservatives used 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 scientists disagree about what the results mean.
A well-designed British study from 2007 has sparked renewed interest in the role of additives. The results convinced the United Kingdom's Food Standards Agency (similar to the U.S. Food and Drug Administration) to urge food manufacturers to remove six artificial coloring agents from foods marketed to children in Britain.
This carefully controlled study tested the effects of the preservative sodium benzoate and six artificial food colorings on hyperactivity in 153 preschoolers (age 3) and 144 elementary students (ages 8 to 9). The researchers intentionally chose to study healthy children rather than children diagnosed with ADHD. Teachers filled out a questionnaire at the start of the study to assess the children's hyperactivity.
For six weeks, the children were given foods and drinks free of sodium benzoate and the six colorings. At weeks two, four and six, half the children in each age group drank plain juice (placebo) and the other half drank juice containing additives. They did this every day for a week. The younger children's drinks had the equivalent of food additives found in one bag of sweets. The older children got varying amounts of food additives in their drinks an amount equal to what is in either two or four bags of candy.
Parents and teachers assessed the children's behavior using standard clinical measures. The children were also evaluated at school by independent reviewers.
The researchers found a slight but significant increase in hyperactivity in children in both age groups during the weeks they consumed drinks containing additives. And it didn't matter what the children's hyperactivity levels were before the study began. These findings confirmed an earlier study the researchers did with another group of 3-year-old children.
Researchers at Columbia and Harvard universities found similar results when they analyzed 15 studies on artificial food coloring in children's diets.
The results are interesting, but the authors of these studies warn that relatively few children are affected by artificial additives. They also point out that determining which children are affected by additives is difficult. Some experts have recommended testing children with ADHD for food reactions, but there's no test that can do this just yet.
Parents could try removing the major sources of artificial colors and additives from their chilren's diets for a few eeeks, and see if symptoms improve. The major sources are candy, junk food, brightly-colored cereals, fruit drinks and soda. But behavior may be more about parental perception than anything that children are eating.
One frequently cited study shows how parents' expectations may color their perceptions when it comes to food-related behaviors. 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 (an artificial sweetener). In reality, all the boys were given aspartame. The mothers who thought their sons ate a large amount of sugar reported significanly more hyperactive behavior, compared with the mothers who thought their sons had the artifical sweetener.
Essential fatty acids are necessary for basic cell functioning, overall immunity and heart health. The body cannot make essential fatty acids. They must come from the diet. One type of fatty acids, omega-3s, are found in salmon, tuna, other cold-water fish, and from some seeds and oils. The other type, omega-6s, are found mostly in vegetable oils.
A balance of omega-3 and omega-6 fatty acids is best for overall health. But the typical American diet has too few omega-3s. Given the importance of these fats to brain health, researchers have explored whether a lack of omega-3s might contribute to symptoms of ADHD.
Only a few randomized, controlled studies have looked at omega-3 supplements for children with ADHD. The American Psychiatric Association's (APA) Omega-3 Fatty Acids Subcommittee published a report in 2006 after looking at five of these trials. They could not determine the specific benefit of omega-3 supplements because of how the studies were designed. Other studies published since then have not resolved the question of whether omega-3 or omega-6 supplements might help children with ADHD. Future clinical trials may provide the answers.
In the meantime, the APA subcommittee recommends that children with ADHD get the recommended amount of omega-3 fatty acids that are part of a healthy diet. For children this means up to 12 ounces (two average meals) a week of a variety of fish and shellfish that are low in mercury: shrimp, canned light tuna, salmon and pollock, plus daily plant sources of unsaturated fats.
Studies have shown that children with ADHD have deficiencies of particular vitamins or minerals such as zinc, iron, magnesium and vitamin B6. But studies testing whether vitamin or mineral supplements reduce 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.
As much as we'd like to find a simple dietary solution for ADHD symptoms, there's only limited evidence for restricting preservatives or artificial food colorings, consuming more omega-3s, or taking specific vitamins or minerals.
For now, the best advice is for children with ADHD to follow the same sensible diet that is recommended for all children:
A healthful diet that has fewer artificial colors and additives and more omega-3 fats and micronutrients may or may not reduce ADHD symptoms. But there is nothing to lose by following a diet that improves overall health and nutrition. And such a diet sets the stage for a lifetime of good health.
Michael Craig Miller, M.D. is editor-in-chief of the Harvard Mental Health Letter and an assistant professor of psychiatry at Harvard Medical School. Dr. Miller has an active clinical practice and has been on staff at Beth Israel Deaconess Medical Center for more than 25 years.