Calcium is the most abundant mineral in the body; 90% of it is stored in the bones. Even though calcium is the main mineral of bones and teeth, it is also found in body fluids where it is involved in other important roles such as muscle contraction, nerve function, blood clotting, and maintenance of normal blood pressure. Besides that, adequate calcium intakes are linked to reduced risk of certain cancers, kidney stones, hypertension, high blood cholesterol, and obesity.
The Dietary Guidelines for Americans Committee has included calcium in the list of nutrients of concern, meaning that most Americans don’t meet the adequate intake of calcium. Low calcium intakes are associated with low bone mass, which increases the risk for osteoporosis, especially for women. Calcium deficiency may also impair growth in children. The principal determinant of bone health is peak bone mass, which is achieved around age 30. After that, bones tend to lose minerals, becoming less dense. Thus, optimal calcium intakes during the years of bone growth is vital to obtain a healthy peak bone mass. Furthermore, when dietary intakes are low, the body releases calcium from the bones into the bloodstream. If low intakes persist for long periods of time, bones become less dense and more fragile, increasing the risk of fractures.
Common calcium sources are milk and dairy products, small fishes consumed with bones such as sardines and canned salmon, green vegetables such as broccoli, kale, and collards, and calcium-fortified beverages and foods (soy milk, almond milk, orange juice, and breakfast cereals, among others). Information about calcium is mandatory on food labels, so be sure to check the package of processed foods. Keep in mind that daily values of 5% or less is considered low, 10% is considered good, and 20% or more is considered high.
Adults absorb around 25% of the calcium present in foods, whereas young people tend to have better absorption capacity than older adults. The best source of calcium is milk and its products, because these foods also contain vitamin D and lactose, which tend to enhance absorption. Calcium absorption may be limited by some food components such as phytic acid found in fruits, vegetables and whole grains, oxalic acid found in beet greens and spinach, and polyphenols found in tea. Also, vitamin D deficiency, excessive intake of phosphorus, and diarrhea may hinder calcium absorption.
The adequate intake of calcium for adults is 1,000 mg/day and 1,200 mg/day for older adults. Calcium supplementation may be used by people who don’t consume milk products, and it is usually considered safe. However, the upper limit for calcium is 2,500 mg/day, based on research that links greater intakes to increased risk for kidney stones. The USDA’s “My Plate” suggests that adults consume around three cups of milk (or dairy products) daily in order to get the recommended amount of calcium.
References
Boyle, M. and Long, S. Personal Nutrition. Belmont, CA: Wadsworth Cengage Learning. 2010.
“How much food from the Dairy Group is needed daily?” Available at http://www.choosemyplate.gov/foodgroups/dairy_amount.aspx. Accessed in Dec. 2011.
United States. U.S. Department of Agriculture and U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2010. Washington, DC: U.S. Government Printing Office. 2010.
Wardlaw, G. and Smith, A. Contemporary Nutrition. New York: McGraw-Hill. 2009