Calcium and Vitamin D
It's recommended that you try to get enough calcium from your diet.
However, combined calcium and vitamin D supplements are often given alongside other osteoporosis treatments, especially if you struggle to get enough from other sources.
Vitamin D is needed for the body to absorb and process calcium.
If you're a woman over 70 and take a calcium-only supplement, don't have more than the recommended daily intake, as there have been concerns that this may affect heart health. This seems to apply only to supplements and not calcium from food.
Read more about calcium and vitamin D.