Q. How were RDAs for calcium determined in the US? In some countries, requirements are lower.
A. Bess Dawson-Hughes, MD, director of Tufts' HNRCA Bone Metabolism Laboratory, answers: "The RDA in the US is determined from calcium balance and retention studies [which compare calcium intake with calcium absorption and excretion] with supporting evidence from double-blind clinical trials of calcium supplementation. Calcium requirements vary around the world because they are influenced by other components of the diet that vary around the world. For example, dietary fiber can reduce calcium absorption. High sodium (salt) intake increases calcium losses through the urine." Dietary calcium sources are best, such as:
- 1 cup 1% milk: 305 milligrams (mg) calcium
- 1 cup calcium-fortified orange juice: 349 mg
- 3 oz canned sardines with bones: 325 mg
- 1 cup calcium-fortified soy milk: 299 mg
- 1/2 cup firm tofu with calcium sulfate: 253 mg
- 5.3 oz low-fat, plain Greek yogurt: 175 mg
- 1/4 cup almonds: 96 mg
Note: The calcium RDA for adults is 1,000–1,200 mg.