The Relationship between Calcium and Iron Absorption
About Calcium
Of all the minerals in the human body, calcium is the most abundant, and one of the most important. Crucial in muscle contraction, bone health, protein function, nervous system function, the vascular system, and cellular signaling, there are few if any areas of the body where calcium is not essential. The importance of calcium means it is crucial that the body maintains an adequate supply of the mineral; however too much calcium in the blood can be just as harmful as too little.
The vast majority of the body’s calcium is stored in bones and teeth, which are constantly being remodeled and renewed. This continual remodeling occurs because calcium is absorbed and deposited depending on blood calcium requirements. When blood levels of calcium are too high, calcium is deposited in bones. If blood calcium levels drop too low, it is absorbed into the bloodstream until an adequate level is reached.
About Iron
As a mineral component of hemoglobin, the protein molecule that carries oxygen in the blood, iron is of equal importance to calcium. This is the most important role of iron in the body, but it is by no means the only one.
In addition to oxygen transportation, iron is an essential component of hundreds of other proteins in the body. It is important in the synthesis of ATP, the unit of energy used by all cells in the body. In addition, iron has antioxidant properties, and plays a role in DNA synthesis.
Calcium and Iron Absorption
Adequate levels of calcium and iron are maintained primarily via intake of these minerals in the diet, in foods and supplements. This can be problematic, however, as there is a significant body of research which shows that dietary calcium can reduce dietary iron absorption. Even a reasonably small amount of calcium, such as that in a portion of milk or cheese, can reduce iron absorption significantly.
The main implication of research on calcium and iron absorption is that taking calcium supplements at meals can prevent some people from obtaining adequate dietary iron. This issue affects women more than men, mostly because women are more likely to take high-dose calcium supplements.
One way to circumvent the problem is by taking calcium supplements only once a day, and taking the supplements at meals where dietary iron is low. The high-iron meals are therefore not affected by the presence of large doses of calcium.
This type of meal planning is important even when supplements are not used, as at least one study has shown that absorption of iron from food is reduced by the presence of dietary calcium in addition to supplemental calcium. In this study, consumption of dairy products along with a high-iron meal reduced absorption of iron by up to 60% (Hallberg et.al.).
References
Hallberg L, Rossander-Hultén L, Brune M, Gleerup A. 1992. Calcium and iron absorption: mechanism of action and nutritional importance. Eur J Clin Nutr. May;46 (5):317-27.
JD Cook, SA Dassenko and P Whittaker. 1991. Calcium supplementation: effect on iron absorption. American Journal of Clinical Nutrition, Vol 53, 106-111.
National Institute of Health Office of Dietary Supplements: Dietary Supplement Fact Sheet: Calcium
Oregon State University Linus Pauling Institute: Micronutrient Information Center: Calcium
Oregon State University Linus Pauling Institute: Micronutrient Information Center: Iron
Sean R. Lynch. (2000). The effect of calcium on iron absorption. Nutrition Research Review. 13, 141-158.
