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Calcium: A Strong Part of Your Diet
From childhood, through high school sports, adulthood, and even into elderly ages, necessary bone construction and remodeling depends on dietary intake of its raw materials: protein, phosphorous, and especially calcium (1). For this reason calcium is essential for building healthy bones and, equivalently, strong teeth. It is also for this reason that insufficient calcium intake increases the risk of developing osteoporosis, other bone loss, or of suffering a bone fracture (2). Beyond these well-known needs for adequate calcium, the mineral is a nearly ubiquitous second messenger, an ion necessary for cellular responses to hormones and other signaling molecules. Indeed, calcium is essential for muscle contraction (in the heart, arms and legs, the diaphragm, as well as muscles throughout the gut), proper signal transmission from nerve to nerve, blood clotting, and releasing compounds from glands (2). It may be hard to believe that the bony support system of the body is continually being remodeled, but bone is an incredibly dynamic structure, capable of self-degradation to release calcium when dietary intake alone is insufficient to support muscle contraction and neuronal signaling (1). Thus, the skeleton acts as a calcium reserve to ‘protect’ the biochemical functions mediated by calcium. Secondary support of these functions is provided by a hormone loop responsible for regulating blood levels of calcium (2). Because calcium is vital to proper function of tissues throughout the body, it is unsurprising that inadequate calcium consumption increases the risk of colon cancer, hypertension, and kidney stone formation (2). Low calcium intake has also been associated with exacerbation of polycystic ovarian syndrome (3), and more recently, with human obesity (4, 5). Dr. M. B. Zemel of the University of Tennessee (and colleagues) has found that a reduced calcium intake ultimately favors fat accumulation and storage. When blood calcium is low, parathyroid hormone (PTH) is released. PTH stimulates bone matrix degradation so calcium is returned to the blood, and this results in high blood levels of a form of vitamin D and high levels of intracellular calcium. In adipocytes, or cells that store fat, high intracellular calcium levels favor fat formation as opposed to fat breakdown (5). Correspondingly, adequate calcium intake tends to increase fat breakdown while decreasing fat formation, thereby reducing body fat and the risk of obesity. Further studies have supported the relationship between changes in fat mass and calcium consumption (6). Recently, however, Dr. Jack Yanovski reported at the annual meeting of the Obesity Society that calcium fails to aid in weight loss when consumed as a calcium carbonate supplement. Dairy or foods with calcium may also contain compounds that activate or act with calcium to create antiobesity effects, and this could explain the contradictory results presented by Dr. Yanovski (7). Despite campaigns such as the CDC’s Powerful Bones. Powerful Girls. and Dairy Management Inc.’s 3-A-Day Dairy that stress the importance of calcium for building healthy bones and teeth, Americans routinely fall short of the daily recommended calcium intake of 1300 mg (8). Some calcium-rich foods include all dairy products such as yogurt, cheese (especially cottage and ricotta), milk, and products made with milk or cheese; dark green vegetables like collards, broccoli, and kale; soybeans and tofu made with calcium; fish with edible bones; almonds; and other products now made with added calcium like orange juice, oatmeal, and cereal (8). REFERENCES 1. Heaney, R. P. “Calcium, Dairy Products, and Osteoporosis.” J Am Coll Nutr 2000. 19 (90002): 83S – 99S. 2. Heaney, R. P. “There Should be a Dietary Guideline for Calcium.” Am J Clin Nutr 2000. 71(3): 658 – 660. 3. Thys-Jacobs, S.; Donovan, D.; Papadopoulos, A.; Sarrel, P.; Bilezikian, J. P. “Vitamin D and Calcium Dysregulation in the Polycystic Ovarian Syndrome.” Steroids 1999. 64: 430-5. 4. Zemel, M. B. “Role of Calcium and Dairy Products in Energy Partitioning and Weight Management.” Am J Clin Nutr 2004. 79 (suppl): 907S – 12S. 5. Zemel, M. B. “The Role of Dairy Foods in Weight Management.” J Am Coll Nutr 2005. 25(90006): 537S – 546S. 6. DeJongh, E. D.; Binkley, T. L.; Specker, B. L. “Fat Mass Gain is Lower in Calcium Supplemented than in Unsupplemented Preschool Children with Low Dietary Calcium Intakes.” Am J Clin Nutr 2006. 84(5): 1123 – 7. 7. Walsh, N. “Calcium Fails to Aid in Weight Loss.” This Week in Medicine. 15 Nov 2006. MD Consult Elsevier Global Medical News 26 Nov. 2006 http://home.mdconsult.com.proxy.lib.umich.edu. 8. U.S. Department of Health and Human Services.
“Calcium Intake Tools.” Mar. 2005. Excerpted from “The 2004
Surgeon General’s Report on Bone Health and Osteoporosis: What it Means
to You.” U.S. Department of Health and Human Services, Office of the
Surgeon General 26 Nov. 2006
http://www.niams.nih.gov/bone/hi/calcium_intake.htm |
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