Calcium doesn't work all by itself to build bones, so it's a good idea to see what other things you're including in your diet. Magnesium absorption helps to drawn calcium into the bone, which is why calcium supplements are usually sold as Cal-Mag combinations. Magnesium also helps to stimulate hormones that keep existing bone intact, as well as speed recovery of bones that break down. Magnesium is found in leafy green vegetables, such as kale and broccoli. Try to avoid vegetables which contain oxalates, such as spinach.
Oxalates are compounds which prevent calcium absorption.
Vitamin C is also needed for bone building and repair. Vitamin C increases calcium absorption and enhances the effects of Vitamin D . Vitamin D is needed to help to body absorb and deposit calcium into bone tissue. Magnesium helps to convert Vitamin D into its active form for this purpose. Vitamin C can't just be found in oranges and grapefruits, though.