Factors That Affect Calcium Absorption

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Calcium is the most abundant mineral in the human body. It is also one of the hardest minerals to absorb from dietary sources. Dr. Elson Haas, author of "Staying Healthy with Nutrition," estimates that 30 to 80 percent of dietary calcium isn't absorbed by the body. Supplemental calcium is often chelated, or combined with protein molecules called amino acids, to help the body absorb them during digestion. Alternatively, calcium supplements could be taken with magnesium at bedtime or between meals due to the acid environment needed in the stomach to assimilate the calcium. Always consult a physician before beginning a new supplement regimen.

Calcium deficiency can lead to bone loss and osteoporosis.


Calcium is found in many foods, and it is ideal to obtain all needed vitamins and minerals from dietary sources. However, in the case of calcium, some foods contain substances that decrease optimal absorption. Foods that are high in oxalic acid such as spinach, chard and chocolate, reduce absorption. Oxalic acid binds with the calcium to form an insoluble salt crystal, which is then carried through the digestive system and eliminated. Phytic acid, which is found in whole-grain foods and high-fiber foods, effects calcium absorption the same way.


Natural calcium absorption becomes less effective as the body ages. Infants and children absorb an estimated 50 to 70 percent of dietary calcium. Adults absorb only 30 to 50 percent of calcium. Elders absorb around the same amount of calcium as the average adult; however, the diet of elders often may include less dietary calcium, putting them further at risk for calcium deficiency. According to the University of Maryland Medical Center, those aged 51 and older should be getting a recommended 1,200 mg daily.

Vitamin D

Vitamin D is a substance that is created naturally in the body. Sunlight exposure stimulates and increases production of vitamin D in the body naturally. This vitamin works in the digestive tract to absorb calcium into the blood stream from the walls of the duodenum, or first part of the small intestine. Vitamin D also helps maintain normal blood calcium level, which is essential to life and to cardiac function. A calcium supplement taken within 1 to 2 hours of sunlight exposure allows the vitamin to enhance absorption. Vitamin D is also available as supplemental oral drops.


Phosphorus is a mineral found in soft drinks that have added phosphoric acid. Phosphorus is also found naturally in some foods and is needed in the body for optimal health. However, too much phosphorus in the diet can lead to extra calcium loss in the urine. This calcium loss in the body can lead to calcium being pulled out of the bones as the body tries to compensate for the missing calcium in blood circulation. This loss of bone density due to calcium depletion is a contributing factor to osteoporosis.


Pregnancy effects calcium absorption in a substantial way. Pregnant women lend all of their available vitamins and minerals directly to the growing fetus. Any substance that is needed in the womb is taken from the mother's body and supplied to the child. This action ensures the baby will get all of the calcium he needs, while depriving the mother of her nutrients unless she is absorbing and assimilating enough calcium for herself and the child. University of Maryland's Medical Center recommends a pregnant or lactating woman should get about 1,000 mg of dietary calcium every day. Bodily calcium stores can be hard to replace in later years because of aging, leading to decreased absorption, so this is an important to time to ensure dietary needs are being met for both the baby and the mother.

Hydrochloric Acid and Stress

Hydrochloric acid, or HCL, is secreted in the stomach during digestion to begin breakdown of dietary fats. HCL is needed for absorption of calcium in the duodenum, which is the first part of small intestine. The duodenum is where calcium is actively absorbed from food into the body through the intestinal wall into the bloodstream. Stress can have a negative effect on HCL production in the stomach and on normal digestive behavior in the body, and can therefore have a negative effect on calcium absorption.

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