Spinach and Calcium Absorption

Spinach provides significant amounts of micronutrients, including manganese, folate and vitamins A, C and K. Regularly eating spinach may even help lower your risk for health conditions such as heart disease, cancer and age-related macular degeneration, according to Drugs.com. Unfortunately, spinach may also interfere with calcium absorption.

A cup of raw spinach has 29.7 milligrams of calcium, or 3 percent of the daily value. Eat a cup of cooked spinach instead, and you'll be consuming 244.8 milligrams of calcium, or 24 percent of the DV. The calcium in spinach, however, isn't all available for absorption. Only about 24 percent of the calcium in spinach is available to your body, according to a study published in the "Asia Pacific Journal of Clinical Nutrition" in 2003. Other green leafy vegetables, such as kale, have a lot more bioavailable calcium than spinach.

Spinach contains a substance called oxalate, which binds to calcium and makes it unavailable for absorption. This mainly affects the calcium found in the spinach, and not calcium found in other foods eaten at the same meal, according to the University of Arizona Extension. The 2003 "Asia Pacific Journal of Clinical Nutrition" study, however, noted that eating spinach with other calcium-rich foods lowered the amount of free oxalate, which means that the oxalate may bind to the calcium in other foods at the same meal as well to some extent.

Another substance that can interfere with calcium absorption is insoluble fiber if it is consumed in high amounts. A cup of cooked spinach contains about 4.3 grams of fiber, or 17 percent of the DV, of which about two-thirds consists of insoluble fiber. This isn't a particularly high amount of insoluble fiber, but if you eat a lot of other fiber-rich foods during the day, it could contribute to a small decrease in calcium absorption.

You can increase the amount of calcium you absorb by spreading out your intake of calcium throughout the day, getting plenty of vitamin D in your diet and not consuming tea and foods containing phytates or oxalate at the same time as you eat calcium-rich foods. Phytates are found in whole grains, nuts, seeds, beans and soy, and foods containing oxalate include rhubarb, beans, sweet potatoes and collard greens.