Professor Philip Shaw discusses research that indicates very few environmental factors that very directly cause ADHD, though there may be many gene-environment interactions.

The role of the environment in ADHD has really attracted a lot of interest. There are several things we know are definitely associated with ADHD. Lead is a very good example. High levels of lead in the environment and high levels of lead in the blood are very clearly associated with ADHD. There are also prenatal factors, like if a mom smokes, for example. The risk of the child having ADHD is greatly increased. And that is particularly the case if the child has a certain genotype or gene makeup. There are lots of different genes which influence ADHD. One of them is of the dopamine transporter. It is called the DAT gene, and if a kid has a certain form of the DAT gene and mom smokes, their risk of having ADHD is very, very elevated indeed. So that’s a good example of how environmental risks interact with the genotype of the child. Other ones that are very well known are dietary factors. These are much more controversial, but there is certainly a good very large study from Southampton that shows that some food additives and colorants may have a very slight effect on the level of hyperactivity in all kids. This isn’t just ADHD. It’s not that it’s going to cause ADHD, but a lot of food additives and colorants may well have a slight effect in making a child a little bit more hyperactive. But I think, though, with some very big exceptions such as lead, there are very few environmental factors that very directly cause ADHD. It seems to be they have a complex interaction with the genetic makeup of the child, and just as it takes lots of genes to make up ADHD, so there may well be lots of different environmental factors involved.

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