Calcium recommendations vary depending on age and special needs. In addition, levels of estrogen can affect calcium needs in women.

The U.S. Department of Agriculture has a PDF file that lists these recommendations.

Vitamin D is required for adequate amounts of calcium to be absorbed into the body, and for adequate calcium levels to be maintained. Therefore, when choosing calcium supplements, those that also contain the RDA of vitamin D are preferred.

Comparing the RDA to the food sources of calcium helps to put the RDA in perspective:

• 8-ounce glass of milk = 300 milligrams
• 2 ounces of Swiss cheese = 530 milligrams
• 6 ounces of yogurt = 300 milligrams
• 2 ounces of sardines with bones = 240 milligrams
• 6 ounces of cooked turnip greens = 220 milligrams
• 3 ounces of almonds = 210 milligrams

A total intake of up to 2,000 milligrams per day from dietary sources and supplements appears to be safe. The preferred source of calcium is calcium-rich foods such as dairy products.