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For post menopausal women, the current recommendation is a total (from diet and supplements) of 1200mg to 1500mg of calcium; and 800mg of vitamin D.
Dairy products are one of the best sources of both calcium and vitamin D. One cup of low fat milk provides about 280mg of calcium and 100mg of vitamin D. So, for instance, if she drank two cups of milk (or had 1 serving of milk and one serving of yogurt) each day, she would still need about 700 to 900mg of calcium, and 600mg of vitamin D.
Calcium supplements come in different types (calcium carbonate, calcium citrate, etc).
There may be considerations in the type of calcium to take, and when to take it if she takes other medications. You can also get calcium supplements that have vitamin D added. Calcium supplements should be taken in divided doses since more than 500mg may not all be absorbed. And some calcium is better on an empty stomach (calcium citrate), while other calcium is fine being taken with a low-iron containing meal.
Since older women often have other health conditions and take prescription medications, it is always best to discuss supplementation (of anything) with her doctor before proceeding. There are many medications that calcium, especially, can interact with.