Calcium has many other uses. It's an ingredient in many antacids. Doctors also use it to control high levels of magnesium, phosphorus, and potassium in your blood. There's good evidence it can help prevent or control high blood pressure. It may also ease PMS symptoms and play a role in preventing certain cancers. Some research shows that calcium with vitamin D, for instance, may help protect premenopausal women from breast cancer. Calcium also has been studied as a weight loss aid. But so far, these studies have been inconclusive.