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vitamin D general
Vitamin D refers to a group of fat-soluble secosteroids responsible for increasing intestinal absorption of calcium, iron, magnesium, phosphate, and zinc. In humans, the most important compounds in this group are vitamin D₃ and vitamin D₂
Absorb calcium and Phosphorus. Essential for developing structure and strength of the bone. Prevent hypocalcemic tetany.
Block the release of parathyroid hormone. This hormone reabsorbs bone tissue, which makes bones thin and brittle.
Vitamin D may also play a role in muscle function and the immune system.
Other roles of vitamin D may include:
Cardiovascular function, for a healthy heart and circulation
Respiratory system –for healthy lungs and airways
Produced endogenously when ultraviolet rays from sunlight strike the skin and trigger vitamin D synthesis. Vitamin D obtained from sun exposure, food, and supplements is biologically inert and must undergo two hydroxylations in the body for activation. The first occurs in the liver and converts vitamin D to 25-hydroxyvitamin D [25(OH)D], also known as calcidiol. The second occurs primarily in the kidney and forms the physiologically active 1,25-dihydroxyvitamin D [1,25(OH)2D], also known as calcitriol .
Food sources (diet)
The best way to get enough vitamin D every day is to eat a variety of healthy foods from all food groups. The vitamin content of various foods is shown in the table.
Vitamin D Content of Various Foods
IUs per serving*
Cod liver oil, 1 tablespoon
Swordfish, cooked, 3 ounces
Salmon (sockeye) cooked, 3 ounces
Tuna, canned in water, drained, 3 ounces
Orange juice fortified with vitamin D, 1 cup
Milk, vitamin fortified, 1 cup
Yogurt, fortified with 20% of the daily value of vitamin D, 6 ounces
Margarine, fortified, 1 tablespoon
Sardines, canned in oil, drained, 2 sardines
Liver, beef, cooked, 3 ounces
Egg yolk, 1 large
Cereal, fortified with 10% of the daily value of vitamin D, 1 cup
Cheese, Swiss, 1 ounce
*IUs = International Units.
Source: Vitamin D. Health Professionals. Dietary Supplement Fact Sheet. National Institutes of Health. Office of Dietary Supplements. June 24, 2011
It is important to check product labels, as the amount of added vitamin D varies when it is artificially added to products such as orange juice, yogurt, and margarine.
Rickets and osteomalacia are classic vitamin D deficiency diseases.
In children, vitamin D deficiency causes rickets, which is a softening or weakening of the bones.
In adults, vitamin D deficiency can lead to osteomalacia, which causes weak bones and muscles.
People who may be at a high risk for vitamin D deficiency include those who are elderly or obese, those with limited sun exposure, and babies who are exclusively breastfed. People who have conditions such as cystic fibrosis (mucus build-up in the lungs) or inflammatory bowel disease are also at risk for vitamin D deficiency.
The main consequence of vitamin D toxicity is a buildup of calcium in your blood (hypercalcemia), which can cause poor appetite, nausea and vomiting. Weakness, frequent urination and kidney problems also may occur.