A British study published in the Lancet has documented the effects of certain specific food coloring agents (sunset yellow coloring, also known as E110; carmoisine, or E122; tartrazine, or E102; ponceau 4R, or E124; the preservative sodium benzoate, or E211; and other colors) and preservatives (primarily sodium benzoate) in kid's drinks. Over 300 children, roughly split between three and eight year olds, underwent the blinded trial. The results were striking: the drinks with additives were linked with higher rates of impulsivity, inattention, and general hyperactivity.
Critics of the study were quick to point out that this is simply an association, not a "cause-and-effect" phenomenon. True enough, but many variables were controlled in this research: drinks, which were given to children in a double-blind fashion, were the only sources of additives. Assignment of the laced drinks was random. And this study builds on previous data gathered by the British government (which is why it awarded over $1 million for this recent research).
So, in my opinion, we are beginning to get scientific backing to the herbalist's idea that synthetic food additives are not only damaging to the liver and metabolism, but also interfere with the psyche. In fact, as many herbalists might tell you, the link between the liver and the spirit is a very real one, and the metabolism of toxic synthetics can lead to inflammatory processes all over the physiology, not just in the nervous system. Back to whole, local foods!