When I was a kid, there was a boy in my class called Jeroen. At times I found him friendly and funny, but other times he would drive me insane with his hyperactive behaviour, jumping around and pulling my hair. Then one day, he told us that we wasn’t aloud to eat anything with artificial food colours anymore. This was supposed to reduce his hyperactivity. I was hopeful, but also sceptical if this would work.
Now that I’m involved in an international consortium investigating food and behaviour, I finally had the chance to learn about food colours and ADHD. Turns out, there is some truth to the claim, although it may only be true for some children, and it may not be specific to ADHD.
A shitty story
To better understand the effects of food on behaviour, we need to start at the end. Your poo can actually tell us a lot about the billions of microbes that live in your gut and help to digest the food you eat. For a long time, we didn’t know much about this micro-wildlife, until scientists developed techniques to analyse large amounts of DNA very quickly and cheaply. As every species has unique DNA, researchers can identify all the different species that live in your gut by analysing their DNA from poo. This helps us to better understand the many important roles that the gut bacteria play in your body, including your brain. For instance, certain bacteria produce neurotransmitters from digesting fibres. These neurotransmitters are important for the communication between brain cells.
What does this have to do with ADHD? ADHD is a neurodevelopmental condition, which means that the brain develops differently compared to typically developing children. This influences the functioning of the brain and hence people with ADHD have problems focussing their attention, controlling their impulses and regulating their activity. A disruption in the neurotransmitter system is thought to play a key role in this. While the main cause of ADHD is genetic, environmental factors are also known to increase the risk of the condition, such as smoking during pregnancy, toxins in the environment, and food allergies. Since recently, researchers are investigating the gut bacteria (aka the poo) to better understand how food allergies may trigger ADHD .
The microbes in the gut interact closely with the immune system. During development the immune system has to learn that many foreign substances in the intestines (i.e. food and bacteria) are good and should not be attacked. In a way, it has to learn not to overreact. And this is what happens with food allergies. The over-reaction of the immune system is harmful for both the gut environment and for the brain, especially if it happens very often. Hence, an allergic reaction to food colourings may trigger small changes in the brain that in turn may trigger behaviour such as hyperactivity. How this works exactly is still unknown.
Based on this theory, clinicians and nutritionists are now investigating if special diets can reduce ADHD symptoms . In such a diet, a child is put on a very restrictive diet that eliminates any potentially allergenic substances. To see which food types trigger the symptoms, specific foods are introduced one by one. For some children, this really seems to work well and they can manage their symptoms by not eating certain foods the rest of their lives. The elegance of this method is that it is based on the individual. While one person may need to eliminate food colourings, for another it could be certain fruits, or cow’s milk.
Do artificial food colours cause ADHD? This may be the case for some children. In others, other types of food may trigger ADHD symptoms. And in yet another group of children, their ADHD has nothing to do with food allergies. At the moment, the only way to find out is through trial and error. But only try this under supervision of trained nutritionists and clinicians!
Back to Jeroen. I don’t remember him getting less annoying. Perhaps he was not allergic to food colourings at all, and he should have tried the complete elimination diet or different medication. Or perhaps I was just an eight-year old girl allergic to all boys.
- Dam, S. et al. (2019) The Role of the Gut-Brain Axis in Attention-Deficit/Hyperactivity Disorder. Gastroenterol Clin N Am, 48, 407–431
- Ly, V. et al. (2017) Elimination diets’ efficacy and mechanisms in attention deficit hyperactivity disorder and autism spectrum disorder. European Child and Adolescent Psychiatry, 26, 1067-1079.
This blog was written by dr. Jeanette Mostert. She is a neuroscientist and science communicator. She is involved in the CoCA-project and Eat2beNICE project. In the latter she is learning all about the links between food and mental health.