Pop Chemistry

In the seemingly never-ending series of reports on the health benefits/risks of coffee and soda, I see that drinking soda can weaken your bones. I’ve heard of this before, but this study appears to confirm it. There are basically 2 main theories about the cause. Theory 1 assumes that it’s the caffeine, since caffeine has been linked to a higher risk of osteoporosis. If so, then coffee drinkers have to worry about this too. Theory 2 suggests the phosphoric acid in soda reacts with and removes calcium from the body, which eventually results in its leeching from bones if you are not getting enough from your diet. Since I tend to snack on Tums, I’m probably in steady state with respect to my calcium. Actually I may be safe without the Tums since the article states: “The researchers didn't find an association between cola drinking and lower bone mass in men.” Woot!

I would like to propose a third mechanism for calcium removal. EDTA (ethylenediammine tetraacetic acid) is added to some sodas as a preservative. The ability of EDTA to wrap itself around metal centers would seem to make it a prime candidate for calcium removal. EDTA’s ability to tie up calcium ions is an essential part of the standard titrimetric analysis for calcium. In fact, EDTA should be able to chelate many of the metals inside our bodies provided the pH isn’t too low. So I admit to being pretty surprised the first time I saw EDTA listed as one of the ingredients in Mountain Dew back in the day. Why is EDTA added to soda in the first place? It’s there to prevent the formation of benzene, which was found to be formed by a reaction between sodium benzoate and ascorbic acid back in the late 90’s. Apparently, the reaction is catalyzed by transition metal ions such as Cu²⁺ and Fe²⁺ (usually supplied by the can) and the addition of EDTA to complex those metals solves the problem. Note: Not all sodas contain EDTA. In some cases the manufacturers just decided to remove the ascorbic acid instead.

Follow up: A little more research has revealed that the most common form of EDTA used is the disodium-calcium salt of EDTA. This means that the EDTA cannot be responsible for lowering the levels of calcium in the body. Damn, another personal theory down the drain.