Approximately 99% of total body calcium is in the skeleton and teeth and 1% in blood and soft tissues. Calcium has four major biological functions: 1) structural as stores in the skeleton, 2) electrophysiological - carries charge during an action potential across membranes, 3) intracellular regulator, and 4) as a cofactor for extracellular enzymes and regulatory proteins. Calcium is present in variable amounts in all the foods and water we consume, although the main sources are dairy products and vegetables.

IMPORTANCE: Builds and maintains bones and teeth; regulates heart rhythm; eases insomnia; helps regulate the passage of nutrients in & out of the cell walls; assists in normal blood clotting; helps maintain proper nerve and muscle function; lowers blood pressure; important to normal kidney function and in current medical research reduces the incidence of colon cancer, and reduces blood cholesterol levels. 

Deficiencies: Acute deficiency symptoms are avoided because of the large skeletal stores. Prolonged bone resorption from chronic dietary deficiency results in osteoporosis either by inadequate accumulation of bone mass during growth or increased rate of bone loss at menopause. Dietary calcium deficiency also has been associated with increased risk of hypertension, preeclampsia, and colon cancer. May result in arm and leg muscles spasms, softening of bones, back and leg cramps, brittle bones, rickets, poor growth, osteoporosis ( a deterioration of the bones), tooth decay, depression.

Dietary recommendations: The dietary recommendations set by the 1997 National Academy of Science Panel on Calcium and Related Nutrients are: 210 mg/d for 0-6 month olds, 270 mg/d for 6-12 month olds, 500 mg/d for 1-3 year olds, 800 mg/d for 4-8 year olds, 1300 mg/d for individuals aged 9-18 years, 1000 mg/d for individuals aged 19-50 years, and 1200 mg/d for individuals over the age of 51 years. No alterations for pregnancy or lactation were recommended. The recommended upper level of calcium is 2.5 g/day.

Food sources: Dairy products are the most concentrated, well-absorbed sources of calcium. Few other foods are rich sources of calcium. Foods which can contribute to dietary calcium include firm tofu (chemically set with calcium), dried beans, kale, broccoli, and bok choy. Calcium from oxalate rich foods such as spinach is generally poorly absorbed. Phytates are slightly inhibitory to absorption. Since FDA allows a label claim relating calcium to prevention of osteoporosis, some fortified foods have become available on the market.

Toxicity: Symptoms of calcium toxicity are largely anecdotal. Excess calcium supplementation has been associated with some mineral imbalances such as zinc.

Recent research: Increasing calcium intakes during adolescence increases calcium accretion up to 1300 mg/day and increases bone mineral content. Even in children, bone density determines fracture risk. Calcium and vitamin D supplementation in the elderly reduces incidence of fracture.