What are common causes of hyperactivity?

A common belief is that eating too much sugar will make a person hyperactive. This belief is especially prevalent amongst parents and teachers who claim that children's behavior often get more rowdy, excited and energetic after they eat too many sugary food and drinks (such as candy or soda). One particular study found that the perception by parents regarding their children's hyperactivity depended on their belief as to whether they had been given sugar.