Question: Is it true that some dark leafy greens, such as collard greens, have as much calcium as milk? I’ve heard that the calcium in dark leafy greens is not as “bioavailable.” I understand that to mean that your body cannot use it as easily or readily as the calcium in milk products. What’s the whole story?
Answer: Yes, calcium from some foods is more easily absorbed by the body, because other components of the food may increase or inhibit absorption. The calcium in both dairy products and some leafy greens is considered the most bioavailable, because the body is able to absorb and utilize most of this naturally-occurring nutrient. Here are some examples of calcium-rich foods and how well the body can use them:
|1 cup milk or yogurt||300 mg||Yes|
|1 oz cheese||200 mg||Yes|
|1 cup soy milk||300 mg||Somewhat|
|1 cup fortified orange juice||300 mg||Somewhat|
|1 cup cooked kale, mustard or collard greens||180 mg||Yes|
|1 cup broccoli||50 mg||Yes|
|4 oz canned salmon (with bones)||240 mg||Yes|
|4 oz cooked salmon filet||20 mg||Yes|
|1 cup lentils or beans||50 mg||Not really, because fiber will limit calcium absorption|
|1 cup cooked Spinach or Swiss Chard||120 mg||No, because oxalic acid in these greens prevents calcium absorption|
Things that Increase Calcium Absorption
Vitamin D (15 minutes in the sun or a 400 IU daily supplement will help)
Lactose (why dairy is such a good source)
Protein (why fish with bones, some beans are good sources)
Things that Inhibit Calcium Absorption
Oxalic Acid, found in spinach, Swiss Chard, berries, nuts, tea, and cocoa (these foods will not only not provide calcium, they’ll also prevent the absorption of calcium from other foods if they’re present in the GI tract at the same time)
Fiber and Phytic Acid found in fiber and legumes
What About Fortified Foods?
Fortified soy milk, almond milk, orange juice, energy bars, etc can be good sources of calcium, but they’re not as well-used by the body as naturally-occurring sources like dairy.
Moral of the Story
Best to get most of your calcium from dairy products, broccoli, and leafy greens like kale, mustard greens, collards, turnip greens, and beet greens.