Calcium phosphate combines calcium with phosphorus. The body absorbs it poorly because it dissolves slowly. This makes it less effective than calcium carbonate or calcium citrate for raising blood calcium levels. Manufacturers rarely use it as the main calcium source. Instead, they might add it as a filler or include it in IV nutrition formulas.
Because absorption is limited, calcium phosphate is not a top choice for supporting bones or other calcium-dependent functions. If you decide to take it, swallow it with a meal to improve absorption.
Like all calcium supplements, it can cause constipation, raise calcium levels too high, or interfere with some medications. People with kidney disease or a history of kidney stones should be extra cautious with any calcium product.