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Vitamin D, often called the "sunshine vitamin," is an important nutrient. Its active form, called calcitriol, behaves like a hormone in the body. Vitamin D plays a crucial role in supporting and maintaining bone health. There are few natural food ...
Vitamin D is found in many dietary sources such as fish, eggs, fortified milk, and cod liver oil. The sun also contributes significantly to the daily production of vitamin D, and as little as 10 minutes of exposure is thought to be enough to prevent deficiencies. The term "vitamin D" refers to several different forms of this vitamin. Two forms are important in humans: ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3). Vitamin D2 is synthesized by plants. Vitamin D3 is synthesized by humans in the skin when it is exposed to ultraviolet-B (UVB) rays from sunlight. Foods may be fortified with vitamin D2 or D3. The major biologic function of vitamin D is to maintain normal blood levels of calcium and phosphorus. Vitamin D aids in the absorption of calcium, helping to form and maintain strong bones. Recently, research also suggests vitamin D may provide protection from osteoporosis, hypertension (high blood pressure), cancer, and several autoimmune diseases. Rickets and osteomalacia are classic vitamin D deficiency diseases. In children, vitamin D deficiency causes rickets, which results in skeletal deformities. In adults, vitamin D deficiency can lead to osteomalacia, which results in muscular weakness in addition to weak bones. Populations who may be at a high risk for vitamin D deficiencies include the elderly, obese individuals, exclusively breastfed infants, and those who have limited sun exposure. Also, individuals who have fat malabsorption syndromes (e.g., cystic fibrosis) or inflammatory bowel disease (e.g., Crohn's disease) are at risk.
The Romans used lime (calcium oxide), clacked lime (calcium hydroxide), and hydraulic cement in construction works. Calcium (Latin calx , meaning "lime") was first isolated in its metallic form by Sir Humphrey Davy in 1808 through the electrolysis of a mixture of calcium oxide and mercury oxide. Chelated calcium refers to the way in which calcium is chemically combined with another substance. Calcium citrate is an example of such a chelated preparation. Calcium may also be combined with other substances to form preparations such as calcium lactate or calcium gluconate. Calcium carbonate can be refined from limestone, natural elements of the earth, or from shell sources, such as oyster. Shell sources are often described on the label as a "natural" source. Calcium carbonate from oyster shells is not "refined" and can contain variable amounts of lead. Calcium is the most abundant mineral in the human body and has several important functions. More than 99% of total body calcium is stored in the bones and teeth where it supports the structure. The remaining 1% is found throughout the body in blood, muscle, and the intracellular fluid. Calcium is needed for muscle contraction, blood vessel constriction and relaxation, the secretion of hormones and enzymes, and nervous system signaling. A constant level of calcium is maintained in body fluid and tissues so that these vital body processes function efficiently. The body gets the calcium it needs in two ways. One method is dietary intake of calcium-rich foods including dairy products, which have the highest concentration per serving of highly absorbable calcium, and dark, leafy greens or dried beans, which have varying amounts of absorbable calcium. Calcium is an essential nutrient required in substantial amounts, but many diets are deficient in calcium. The other way the body obtains calcium is by extracting it from bones. This happens when blood levels of calcium drop too low and dietary calcium is not sufficient. Ideall...