Does sugar make children hyperactive?

Few health beliefs are held as firmly as this one: give a child sugar and you get a small tornado. It feels obviously true to anyone who has watched a birthday party. And it is one of the rare claims that researchers have tested directly, repeatedly, and under tight conditions.

What the evidence says

The strong tests here are double-blind trials: children are given either sugar or a sugar-free substitute, and, crucially, neither the children, the parents, nor the observers know which is which. Pooled together in a meta-analysis, these studies have not found that sugar produces the hyperactivity everyone expects. When nobody knows who got the sugar, the tornado does not reliably appear.

So where does the belief come from? A revealing set of studies looked at the parents rather than the children. When parents were told their child had just eaten sugar, whether or not it was true, they rated the child's behaviour as more hyperactive, and watched them more closely. The sugar changed the observer, not the observed.

That does not mean sugar is harmless. There are real reasons to moderate it, dental health and overall diet among them. But causing hyperactivity is not one of the well-supported ones.

Why the myth survives

The belief is kept alive by exactly the machinery it thrives on: parties are chaotic for a dozen reasons, excitement, crowds, late nights, other children, and sugar is present at all of them, so it takes the blame. Expectation does the rest.

This is a case where the science is unusually settled, and settled against the intuition. Believe the trials over the birthday party.

This is an evidence summary for the general reader, not advice about your child's diet or health.