Using a computerized coin flip, the researchers assigned the women to receive daily doses of either alendronate or a placebo for 24 months. All participants in both groups also received vitamin D, which helps the body retain and use calcium consumed in the diet. Calcium supplements were also given to women whose diets did not already contain enough calcium. The researchers measured bone strength (bone mineral density, or BMD) at the lower portion of the spine and at the hip bone. In addition, they did blood tests to evaluate whether the body was making new bone or losing bone. The researchers also kept track of side effects of alendronate.