DudeInNOVA saidDoes anyone know where I can find a good reference on taking vitamins and minerals and how they interact with each other and cancel out each other's absorption?
Here's an example. I want to take more zinc. I checked my multi-vitamin, and it has 100% of my daily value for zinc. Great. Then I read that calcium can block the absorption of zinc. Oh. My multi-vitamin has calcium too. Two supplements that I take (doctor recommended) have calcium as well. My buffered Vitamin C has calcium, but I take that later in the day. So how much zinc am I really getting? I want to take more, but what's the point if it's going to be cancelled out by other supplements that I'm taking?
Any help with this would be appreciated. Thanks.
There isn't in vivo data on this. There is biochemical data that shows that some of the divalent metal cations are absorbed via the same transporters and stored in the same protein (called metallothionein, which you can read about in the wikipedia article: http://en.wikipedia.org/wiki/Metallothionein). There isn't data that specifically says how much of each you need in your specific body. There is also evidence that phytate/phytic acid, a negatively charged molecule will bind the divalent metal cations, but the extent to which this happens hasn't been decided--so we are left with recommendations
Anyone who tells you that there are specific ratios you need is a charlatan nutritionist, of which the US doesn't regulate in most states, and they are happily doing business in the US right now taking money from people like you. The only nutritionists that can lose a certification title for saying crock are registered dietitians, and if you see one saying inaccurate stuff, happily report them to the commission on dietetic registration (CDR). Furthermore, iron is stored separately in a molecule called ferritin, transported in the body in transferrin, and it is used in the production of hemoglobin. Iron also has its own absorption and regulation mechanisms.
If you're eating a varied diet (as in you aren't doing something trendy like paleo, atkins, south beach, diets that completely eliminate certain foods for non-scientifically-substantiated reasons, etc., diets that aren't produced by anyone with a formal nutrition background) and consume a multivitamin daily, you probably aren't at excess or deficiency of any of the minor elements. Conversely, it is unlikely you will reach toxicity (as someone mentioned in this thread) from taking 1 multivitamin a day unless you have some sort of illness/disease/inborn error of metabolism because well-respected multivitamins (not GNC ones, for example) only go over the 100% DV/RDA (whichever they reference) if it's a water-soluble vitamin and poses little risk of toxicity and 2) you have metallothionein, which regulates absorption of potentially toxic minerals via more expression of the protein or it can flake off and be passed out with the stool when your epithelium sloughs off. The upper limit of intake is well above anything in a respected multivitamin.
As someone mentioned, just make sure you are varying your diet. Calcium has a separate set of mechanisms for absorption (via calmodulin from activated vitamin D and it can also be absorbed paracellularly (between the cells).