Calcium is an important mineral that aids in muscle movements, nerve transmissions and the maintenance of strong bones and teeth. Depleted calcium levels can lead to bone disorders and heart problems. Although milk and other dairy products are the most abundant sources of calcium, leafy greens such as spinach also contain high calcium content. However, the calcium bioavailability -- the amount of absorbable calcium -- in raw spinach is relatively poor.
Spinach: High Calcium, Low Availability
The average adult needs about 1,000 milligrams of calcium daily, according to the Office of Dietary Supplements. Raw spinach has low calcium bioavailability due to high amounts of oxalic acid, which binds with the calcium found in spinach, thus reducing its digestibility. Spinach does not deplete other dietary sources of calcium such as yogurt, cheese and milk. However, relying on spinach for calcium can lead to low levels of the mineral in the blood, which may cause bone development issues or an increased risk of osteoporosis. One cup of cooked spinach contains 245 milligrams of calcium, but the body can only absorb about 5 percent --12 milligrams -- while the body can absorb 30 percent of milk’s calcium content.
Don't let spinach's low calcium bioavailability keep you from eating it. It's rich in fiber, protein, vitamins A, C, E, K, thiamine, riboflavin, folate and several minerals. In addition to one or two daily servings of high-calcium dairy foods, such as Greek yogurt and milk, cooked spinach, broccoli and other leafy green vegetables can add to your daily calcium intake.