If you tell parents that their kids have had sugar, they will report those children as behaving hyperactively whether they've actually had sugar or not. It's a consistent outcome.

It's one of those things that you can't convince people of because there's some things they have a deep need to "know."

Other things that you can't convince people of: the caffeine levels in coffee don't really keep people awake (they'll still stay up if you slip them decaf), and that there never were any significant numbers of people putting razor blades in Halloween apples (other than parents looking for attention.)