Was it the sugar or the caffeine?

Was it the sugar or the caffeine?From Reuters, via Mickey:

Oslo teens who drank the most sugary soft drinks also had more mental health problems such as hyperactivity and distress, Norwegian researchers reported on Thursday.

Their study of more than 5,000 Norwegian 15- and 16-year-olds showed a clear and direct association between soft drink intake and hyperactivity, and a more complex link with other mental and behavioral disorders.For hyperactivity, there was a direct linear relationship -- the more sodas a teen drank, the most symptoms of hyperactivity he or she had.The worst problems were seen in boys and girls who drank four or more soft drinks a day. Ten percent of the boys and 2 percent of the girls drank this much.The researchers said it was possible that other substances in the soft drinks, such as caffeine, were to blame for the symptoms, and they did not check other possible sources of refined sugar in the children's diets.

The failure to control for caffeine intake makes it unclear whether this study really demonstrates anything non-obvious. There are anecdotal reports of people who are very affected from non-caffeinated refined sugar products, so the sugar / hyperactivity hypothesis remains a reasonable one. However, studies of large populations have had trouble demonstrating an effect, and this study does not seem to move the ball forward or backward on that question. A possible model for a sugar - hyperactivity link could be yet undiscovered diseases that affect behavior and have a sugar triggers as seen with the muscle disease hypokalemic periodic paralysis.