Tartrazine, also known as Yellow #5, is a coal-tar derivative azo dye found in a lot of processed food, including Kraft Macaroni and Cheese, Doritos, Mountain Dew, Peeps, and many soups, custards, mustards, baked goods, cotton candy, ice cream and tons and tons more. It's also in a million and one other products we may use on a daily basis - lotions, face soaps (including the one I used this morning), body soaps (including the one I used this morning!), cosmetics, shampoos, hand stamps - you name it! Despite this multimodal ingestion and cutaneous exposure, only a very small amount of the dye is used in each product, so total exposure might be around 1 teaspoon in a year (from wikipedia, so take that number with a grain of salt) (The CSPI site says around 12.75mg a day on average based on usage data - but probably more for kids and those who live on Mountain Dew). There's no reason, though, to freak out and empty out the pantry and medicine cabinet. Dose is important. But, as we well know, some of us can bathe in toxic substances and come out smelling like a rose, and others are sensitive to very small amounts.
The reason I'm looking at it more closely today is because if you hunt around the internet searching for possible creepy things about industrial food dyes, tartrazine has the worst reputation. And, indeed, it was one of the several dyes used in the Southampton Study I discussed earlier this week - and the whole study cocktail of dye and preservative did lead to increased hyperactivity in kids. Its use as a food additive is subject to a ban in the UK and voluntary bans in other European countries, like Norway. In fact, the Center for Science in the Public Interest in the US called for the FDA to ban Yellow Number 5 on June 30, 2010. (Here's a cute PDF from CSPI - Food Dyes, a Rainbow of Risk.)
But how might tartrazine cause problems? Well, some people (around 1/10,000, more or less) are definitely allergic to it. Hives, purpura, anaphylaxis, the real deal. This is why the FDA declared that it has to be on the labels of food if it is used - for people with hypersensitivity, and you can run afoul of the FDA if you include tartrazine in your product and don't label it (1). Not unusual - lots of natural and manmade chemicals cause allergic reactions in some people. It would be an unfortunate allergy to have, as yellow number 5 is in all sorts of things you wouldn't expect. Also, there seems to be a cross-reactivity in some people with asthma between tartrazine and aspirin - people with asthma caused by aspirin also seem to have asthma caused by tartrazine (2), and using desensitization techniques (gradual increasing exposure) to reduce aspirin sensitivity in one case study protected against the effects of tartrazine too. (3). Hmmm.
What about other actions of tartrazine? I couldn't find much. One study showed that application of small amounts of tartrazine caused contraction of intestinal muscle cells in guinea pigs, and the effect was blocked by atropine. That clues us in that tartrazine seems to be able to activate the parasympathetic nervous system, either directly or indirectly, via the muscarinic receptor (4). Now that is quite interesting, as the central nervous system has lots of muscarinic receptors of all types known (M1-M5). Various activating agents of these receptors can cause things such as confusion, convulsions, restlessness, and psychosis - in high enough doses. At lower doses they can sometimes do the opposite, and cholinesterase inhibitors (which increase the CNS activity of acetylcholine, a muscarinic activator) are used to treat dementia. We've taken several big leaps at this point, but it is theoretically possible that if tartrazine gets into the central nervous system, this muscarinic receptor activation might be a mechanism for some sort of psychiatric reaction (like increasing hyperactivity).
The most intriguing information comes from this study from 1990 about how tartrazine influences the zinc status of hyperactive children. Now I'm still trying to get my hands on the full text - institutional access website is being coy the last few days, and it seems this journal is only available online from 1995 on anyway. But the abstract is telling. 20 hyperactive boys and 20 "aged matched controls" were tested for zinc levels in their saliva, urine, 24 hour urine, scalp hair, fingernails, and blood. The hyperactive kids had decreased zinc everywhere but the saliva. Then 10 control kids and 10 hyperactive kids were given a tartrazine-containing drink. In the hyperactive kids, the blood levels of zinc went down and the urine levels of zinc went up, and their behavior got worse, suggesting that tartrazine caused them to pee out some much-needed zinc. It's a bit hard to tell from the abstract, but the way I read it, it looks like the control kids zinc levels didn't change, and neither did their behavior. So that might be the mechanism by which yellow number five influences hyperactivity in certain kids. Ironically enough, Concerta, a formulation of Ritalin, has yellow number 5 as a colorant in the capsule!
The only other dirt I found on yellow number five is that it was implicated also in reducing the absorption or metabolism of vitamin B6, leading to carpal tunnel syndrome, of all things (at least according to Dr. Murray). (Here's the link between B6 deficiency and carpal tunnel, anyway). The rumor that the yellow number 5 in Mountain Dew causes your testicles to shrink? Well, that's not true.
My stance is - for most kids there is no need to make a big scene at a birthday party by grabbing the bag of rainbow candy out of your kid's hand. But on a day to day basis, processed food should be avoided in favor of whole, real food anyway. Doing that will reduce exposure to the rainbow soup of chemicals in processed food. Not to mention the mountains of fructose, trans fats, and genetically modified ingredients. Real food is a win/win. Weirded out by yellow number 5 in shampoos and soap? Check the labels if it bothers you. Or use baking soda and apple cider vinegar as cheap alternatives to shampoo and conditioner.