Factors That Favor & Hinder Calcium Absorption

Calcium is required to support the structure and function of bones and teeth, and is also involved in muscle function and nerve transmission. Although there are many food sources of calcium, both dairy and non-dairy, the absorption of this mineral depends on many factors in the diet and will be better absorbed in the presence or absence of certain nutrients.

Protein Foods

High intakes of protein have been found to increase calcium excretion. According to the American Dietetic Association's position paper on vegetarian diets, diets rich in meat, fish, dairy products, nuts and grains produce a high renal acid load. Calcium is reabsorbed from bone to help buffer the acid loss, and there is an increase in calcium loss in the urine. In addition, the ratio of dietary calcium to protein has been shown to be a better indicator of bone health than calcium intake alone in some studies.

Fruits and Vegetables

Fruits and vegetables create a more alkaline environment in the body by producing bicarbonate, reducing calcium loss. Conversely, diets high in protein and cereal grains produce metabolic acids, which cause the bone to release calcium, phosphates and alkaline salts to neutralize the excess acid. According to the National Institutes of Health Office of Dietary Supplements, one study showed that women aged 50 years and older who took bicarbonate supplements showed reductions in calcium excretion.

Oxalates and Phytate

Oxalates, found in foods such as spinach and Swiss chard, reduce calcium absorption significantly. Thus, these vegetables are a poor source of calcium. Low oxalate greens such as bok choy, broccoli, collards and kale are good sources of readily absorbed calcium. Phytate, found in nuts, seeds and grains, may also inhibit calcium absorption. Due to the low bioavailability of calcium in some plant foods, vegetarians who do not consume dairy products will need to particularly aware of their intake.

Vitamin D

Vitamin D, which may be consumed in diet or produced by the skin with exposure to sunlight, increases calcium absorption in the gut. In addition, vitamin D maintains adequate serum calcium and phosphate concentrations to allow for normal bone mineralization. In conjunction with calcium, vitamin D helps to prevent osteoporosis in the elderly. Milk may be fortified with vitamin D, and many calcium supplements are also manufactured to contain both calcium and vitamin D.