A new trend is the addition of calcium with chocolate for calcium supplements, such as chewable calcium supplements. From a marketing standpoint this may sound like a great idea. From a practical standpoint though it is real stupidity. Cocoa, used to make chocolate is a rich source of oxalic acid. Oxalic acid has a high affinity for calcium binding with the calcium and rendering it unusable by the body.
Coffee and teas (black, oolong, and green) are also sources of oxalic acid. For this reason calcium supplements should not be taken with these beverages. Nor should green tea be added to supplements with calcium or be taken with calcium supplements.