Here is Aaron Carroll at The Incidental Economist:
Let’s cut to the chase: sugar doesn’t make kids hyper. There have been at least twelve trials of various diets investigating different levels of sugar in children’s diets. That’s more studies than are often done on drugs. None of them detected any differences in behavior between children who had eaten sugar and those who hadn’t. These studies included sugar from candy, chocolate, and natural sources. Some of them were short-term, and some of them were long term. Some of them focused on children with ADHD. Some of them even included only children who were considered “sensitive” to sugar. In all of them, children did not behave differently after eating something full of sugar or something sugar-free….
In my favorite of these studies, children were divided into two groups. All of them were given a sugar-free beverage to drink. But half the parents were told that their child had just had a drink with sugar. Then, all of the parents were told to grade their children’s behavior. Not surprisingly, the parents of children who thought their children had drunk a ton of sugar rated their children as significantly more hyperactive. This myth is entirely in parents’ heads. We see it because we believe it.
Even when science shows time and again that it’s not so, we continue to persist in believing that sugar causes our kids to be hyperactive. That’s likely because there’s an association. Times when kids get a lot of sugar are often times when they are predisposed to be a little excited. Halloween. Birthday parties. Holidays. We may even be causing the problem ourselves. Some parents are so restrictive about sugar and candy that when their kids finally get it they’re quite excited. Even hyper.
This does not mean that there aren’t a ton of great reasons why our kid should not ingest large quantities of sugar. As almost any parent knows, sugar has been linked to cavities and the obesity epidemic. Just don’t blame it for your child’s bad behavior.