By the way, doctor: How long does calcium absorption take?

Q. I've read that the body can't assimilate more than 500 milligrams (mg) of calcium at a time. How long does this take? I want to allow enough time between taking my 500-mg calcium supplement and drinking a glass of milk.

A. The body can absorb a 500-mg dose of calcium very efficiently — whether from diet or supplements. But as the dose increases above that level, absorption efficiency declines. For example, the body doesn't absorb much more calcium from a single 1,000-mg dose than it does from a single 500-mg dose.

Calcium is mostly absorbed in the duodenum, the first part of the small intestine, which extends from the stomach. Normally, it takes about two hours for calcium absorption to take place. For people with delayed stomach emptying or who have had duodenal bypass surgery, it can take even longer.

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