Foods' reported calcium content may differ from how much of it your body can actually abosrb. Nutrition Diva explains why here.
Q. For foods that are high in oxalates (such as spinach), is the reported amount of calcium adjusted for the fact that you don’t absorb it as well?
A. No, it’s not. Calcium content is based on the amount of elemental calcium in a food, without regard to how much of it gets absorbed. If you look up spinach in a nutritional database, for example, you’ll find that a cup of cooked spinach contains about 230 mg of elemental calcium. However, spinach also contains oxalic acid, a compound that binds to calcium and interferes with your ability to absorb it. As a result, only about 5% of the calcium (or, approximately 11 mg) is actually absorbed. By comparison, a cup of cooked broccoli contains just 70 mg of elemental calcium—but up to 60% of this (around 40 mg) is absorbed. Even though broccoli contains less calcium than spinach, it turns out to be a superior source.
Dairy products like milk, yogurt, and cheese are among the most potent food sources of calcium. But that’s not because the calcium is particularly well-absorbed. Only about a third of the calcium in dairy is taken up by the body, but because these foods are so high in elemental calcium, you end up absorbing about 100mg of per serving. For those who want to dig deeper, here’s an article with lots more on the relative bioavailability of calcium from different foods. But it doesn’t have to be that complicated. The recommended intake for calcium is based on the assumption that you’ll be getting calcium from a variety of foods, some of which are better absorbed than others.
Food sources of calcium from Shutterstock