For decades, researchers have been trying to answer a hotly contested question: Do the synthetic dyes used to add vibrant colors to foods like certain breakfast cereals, candies, snacks and baked goods cause behavioral issues in children?
A bill before the California Senate, which is expected to come to a vote this week, has reignited the debate. If passed, it would prohibit K-12 public schools in California from offering foods containing six dyes — Blue No. 1, Blue No. 2, Green No. 3, Yellow No. 5, Yellow No. 6 and Red No. 40.
Between 1963 and 1987, the Food and Drug Administration approved nine synthetic dyes to be used in foods in the United States, and the agency maintains that they are safe.
Yet some studies have raised concerns that they may have an effect on some children’s behavior.
What the Research Suggests
In the 1970s, a pediatric allergist from California caught the attention of physicians and parents when he suggested that a diet without artificial food colors, flavors and preservatives could help treat the majority of children with A.D.H.D.
That was an enthusiastic but exaggerated claim, said Dr. L. Eugene Arnold, a professor emeritus of psychiatry and behavioral health at the Ohio State University College of Medicine. Ensuing research from the 1980s “pretty much debunked” the idea that strict elimination diets were helpful for treating A.D.H.D., he said, so many physicians concluded that they were ineffective.
But scientists continued conducting trials on one element of the elimination diets — synthetic food dyes — during the next decades.
In most of these trials, parents, teachers or researchers would observe children’s behavior when they consumed the dyes in foods, drinks or capsules, and then compare it with when they consumed placebos. In some studies, researchers also measured their concentration skills with computerized tests.
Early trials were small and had inconsistent results, with some suggesting the dyes increased hyperactivity while others found no effect, Dr. Arnold said.
But in two later trials conducted in Britain and published in 2004 and 2007, each including about 300 children with or without A.D.H.D. symptoms, researchers found a small but significant increase in hyperactivity when the children consumed juices containing dyes.
After these studies, European lawmakers began requiring that foods containing certain dyes carry warning labels about their potential effects on children’s attention and activity.
In 2011, an F.D.A. committee considered requiring similar labels in the United States, but concluded that there wasn’t enough evidence to prove that food dyes caused hyperactivity. It voted against the warnings and recommended more research, yet few studies have been done in the years since, said Dr. Arnold, who summarized the existing research at the 2011 meeting.
In 2021, state scientists from California published a report that put a new spotlight on food dyes. The team, alongside researchers from the University of California, reviewed 27 mostly small trials in children. The conclusion: Food dyes can interfere with normal behavior in at least some kids.
Emily Barrett, a professor of biostatistics and epidemiology at the Rutgers School of Public Health who peer-reviewed the report, said that it was “fair, unbiased and very thorough.”
Joel Nigg, a professor of psychiatry at Oregon Health and Science University, performed a similar review in 2012. He had expected to find evidence that would reassure those who were worried about food dyes, he said. However, he also found a small but significant increase in hyperactivity when children consumed the dyes. Other researchers have come to similar conclusions.
Dr. Nigg and other experts have acknowledged the various limitations with the research. In addition to most of the available studies being small, many are also decades old and some rely on parents’ reports of their children’s behaviors, which can be biased. Some also tested dyes that weren’t used in the United States, making it difficult to say if the results apply to children in this country.
No large, representative studies have been done on children in the United States, Dr. Nigg said. And researchers aren’t sure how, exactly, the dyes might increase hyperactivity; one study in children suggested that regulation of histamine, a neurotransmitter that can affect behavior, may be involved. In some studies on rodents, researchers have also reported that high levels of the dyes could cause cellular damage and affect signaling and structures in the brain.
The F.D.A., along with an international committee of food safety experts, has emphasized the limitations of the research while maintaining that the food dyes currently approved in the United States are safe.
An F.D.A. spokesman said in a statement that while some evidence suggests that certain children may be sensitive to the dyes, most are not affected. The agency will continue to examine this question, he said. It is also currently reviewing the safety of Red Dye No. 3, which will be banned from all foods sold in California starting in 2027 as part of a law signed last year.
The F.D.A.’s approach is to consider the dyes “safe until proven harmful,” Dr. Nigg said. But based on the current evidence, he added, a better strategy would be to prove them safe before they are given to children.
Frank Yiannas, a former deputy commissioner of food policy at the F.D.A., said in an email that the California bill was a direct result of an “F.D.A. that isn’t moving fast enough” to address consumer concerns.
Eyes on California
Many school districts, health providers, health advocates and democratic and republican lawmakers have backed the bill.
It also has the support of many parents in California, like Maritza Arguello, 35, who lives in Riverside. Ms. Arguello no longer gives foods containing synthetic dyes to her young daughter, who has A.D.H.D.
Industry groups, including the Consumer Brands Association, which represents packaged food and drink companies, as well as the International Association of Color Manufacturers and the American Beverage Association, have opposed the bill.
Jim Coughlin, a nutritional toxicologist who has reviewed the research and testified against the bill on behalf of Consumer Brands Association, said that the studies had been too inconsistent to convince him that the dyes were harmful.
But Dr. Nigg said that given the scientific uncertainty — and the fact that dyes add no nutritional value to meals — it makes sense to avoid having them in schools.
“There’s a reasonable suspicion that food dyes may be harmful, at least for some kids,” Dr. Nigg said. “So why expose them to it?”
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