If your child has attention deficit hyperactivity disorder (ADHD), it's not because he or she played too many video games, logged multiple hours of TV viewing, or ate the wrong kinds of foods. In fact, researchers think the cause of ADHD is largely genetic. But it is tempting to look for dietary factors that could be making symptoms worse.
In particular, a possible link between ADHD and certain foods -- including food dyes and preservatives -- has been suspected since the 1970s. Still, despite decades of research, experts can't agree on whether eliminating dye-containing foods from a child's diet can ease ADHD symptoms like hyperactivity and impulsivity -- except in perhaps a few special cases.
"Scientific evidence is limited to support the association between food additives and ADHD symptoms," says Maida Galvez, M.D., director of the pediatric environmental health specialty unit at Mount Sinai School of Medicine, in New York City. "Although it is possible that a very small group of children who are allergic to artificial colorings or preservatives may show improvement in symptoms on restriction diets, evidence is insufficient to recommend routine, widespread use of restriction diets to treat a child's ADHD symptoms."
However, Bernard Weiss, Ph.D, professor of environmental medicine at the University of Rochester School of Medicine and Dentistry, in New York, says it's clear that food additives can sometimes affect child behavior, at least in the short term. He has conducted controlled trials on the topic and says: "From the standpoint at least of acute effects produced by food color consumption, you really can't deny the evidence any more."
For example, a 2007 study published in The Lancet found that a mixture of four artificial food colors plus the preservative sodium benzoate aggravated hyperactivity in two groups of children without ADHD -- three-year-olds and eight- to nine-year-olds. But a second mix didn't have as great an effect on the eight- to nine-year-olds, even though it also contained sodium benzoate and two of the same colorings, albeit in lower amounts.
Part of the controversy lies in the fact that most food products contain more than one dye or preservative (some candy products have as many as 10 dyes). And most studies have looked at blends of additives, not single ingredients, making it difficult to sort out the culprits.
"There's no way to know at this point which is the problem dye. Is only one of them a problem? All of them a problem?" says Michael F. Jacobson, Ph.D, executive director of the Center for Science in the Public Interest (CSPI), which has petitioned the Food and Drug Administration (FDA) to ban all food dyes because of hyperactivity concerns.