For calcium to absorb properly into the body it has to work synergistically with other nutrients. You should take calcium in conjunction with other important minerals such as magnesium, potassium and zinc. Also don't forget Vitamin D, an essential for proper absorption. I'd be careful in purchasing a vitamin complex, a lot of them do not contain enough of the proper minerals or elements that help transport calcium to your bones. Calcium often just sits inside the tissue rendering useless to your system.