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The National Institute of Child Health and Human Development (NICHD) stated in its Mar. 13, 2006 publication for the Milk Matters campaign titled "Building Strong Bones: Calcium Information for Health Care Providers," available on its website:

“Bioavailability, the degree to which the intestinal system absorbs calcium, depends on the overall level of calcium in a food and the type of food being consumed. Calcium in foods such as milk and milk products is highly bioavailable, meaning that it is easily absorbed…

However, calcium in foods high in oxalic acid (such as spinach, sweet potatoes, and beans) or phytic acid (such as unleavened bread, raw beans, seeds, and nuts) may be poorly absorbed. Oxalates in particular are strong inhibitors of calcium absorption. As a result, additional servings of certain calcium-rich foods are needed to compensate for their low bioavailability…

High bioavailability is one of the reasons that the NICHD describes low-fat and fat-free milk and milk products as the best dietary source of calcium.”

Mar. 13, 2006