Calcium is so important to life that your body will take it from your bones if it is not otherwise available. Ninety-nine percent of your calcium is in your bones and teeth. Eating enough foods rich in calcium helps build a healthy skeleton in your youth and helps minimize bone loss in your later years. After your skeletal growth is completed by 16 to 18 years for girls and 18 to 20 years for boys, your bone tissue continues to undergo remodeling in response to needs of your body caused by changes in your diet, microscopic fractures, and changes in lifestyle factors. Your bone remains a dynamic tissue even in your mature skeleton.
Function
Beyond its role in bones and teeth, calcium plays a number of metabolic roles in cells of all other tissues. Calcium influences transport across cell membranes, the release of neurotransmitters, protein hormone function, and the activation and release of enzymes. Calcium is needed to regulate your heart muscle and nerve transmission. Too much calcium in the blood can cause cardiac or respiratory failure. Too little calcium in the blood results in tetany, or muscle twitching and spasms of skeletal muscles.
Nutrition
Calcium occurs naturally in milk and milk products. Other foods, including vegetables such as broccoli and chard, tofu and small fish with bones also provide a source of calcium. Because the bioavailability of calcium in foods varies, your body can absorb more than half of the calcium contained in certain vegetables such as cauliflower, broccoli, brussels sprouts, kale, mustard greens, bok choy and calcium-fortified foods. You can absorb about 30 percent of the calcium in milk, calcium-fortified soy milk and calcium-set tofu, cheese and yogurt. You can absorb about 20 percent of the calcium in almonds, pinto beans, sweet potatoes and sesame seeds. You can absorb less than 5 percent of the calcium in spinach, Swiss chard and rhubarb because of the presence of oxalic acid binders in these foods.
Age
You attain your highest bone density, or peak bone mass, during your first two decades of life. In the bone acquiring stage of childhood and adolescence, it is important to consume calcium-rich foods and beverages to maximize bone mass. Dense bones help protect against age related fractures and bone loss in the bone losing decades beginning at about age 40. As you age, your cells that build bone become less active, but those that dismantle bone continue working. Osteoporosis, or bone loss severe enough to cause fractures, afflicts more than 25 million people in the United States, mostly women past the age of menopause. according to "Understanding Nutrition," a 2002 book by Eleanor Noss Whitney and Sharon Rady Rolfes.
Calcium Balance
Calcium balance is one of your body's highest priorities. Whenever calcium gets out of balance, your body calls into action a system of hormones, vitamin D, your intestines, bones and kidneys to reestablish homeostasis. Your bones provide a bank of calcium for the blood to borrow from and return as needed. Even if your diet is deficient in calcium, it is imperative that blood calcium remain normal to maintain a normal heartbeat, so your bone calcium must diminish by donating to your serum calcium level if that level threatens to fall too low. A chronic dietary deficiency or an inability to absorb calcium, over time, depletes the calcium in your bones. Your body will take calcium from your bones when needed to meet the vital needs of maintaining life. Providing that reservoir of calcium is your bones' primary function, even more important than its role of maintaining skeletal integrity.
References
- "Understanding Nutrition, Ninth Edition"; Eleanor Noss Whitney and Sharon Rady Rolfes; 2002
- "Krause's Food, Nutrition, & Diet Therapy, 10th Edition"; Kathleen Mahan and Sylvia Escott-Stump; 2000
- University of Maryland Extension: Eat Smart Be Fit: Healthy Eating: Calcium Corner
- MayoClinic.com; Calcium Supplements and Bone Health; Jennifer Nelson, MS, RD, Katherine Zeratsky, RD; Aug. 21, 2010
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