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vitamin D

Posted on 09. Dec, 2010 by .

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Vitamin D
Vitamin D is a fat-soluble vitamin that helps the body absorb calcium. Fat-soluble vitamins are stored in the body’s fatty tissue.
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.
In addition to helping the body absorb calcium, vitamin D also helps the body keep the right amount of calcium and phosphorus in the blood.
Vitamin D and nutrition
Over the last few hundred years human lifestyles have changed. The industrial revolution resulted in more indoor work and less exposure to sunlight. Many societies around the world wore more clothing over the centuries, further reducing skin exposure to sunlight. These changes have brought with them a significant reduction in the natural production of vitamin D and subsequent diseases.

Countries responded to these changes by fortifying some foods with vitamins D2 and D3, examples include breakfast cereals, bread, pastries, oil spreads, margarine, milk and other dairy products. Initially, some scientists complained that nutritional fortification and recommended supplementation doses were not making up for the shortfall. These people were ignored, and sometimes ridiculed – however, over the last few years studies indicate that they may have been right after all.

Not that many foods contain vitamin D. Some fish, such as salmon, tuna and mackerel, as well as fish liver oils are considered to be the best sources. Some vitamin D is also present in beef liver, cheese and egg yolks. Most of these are Vitamin D3. Some mushrooms provide variable amounts of vitamin D2.

Most of the food sourced vitamin D in the western diet comes from fortified foods – where vitamin D is artificially added. Most US milk is fortified with 100 IU/cup of vitamin D. In the 1930s milk was fortified in many countries to combat rickets, which was a major health problem then.
Side Effects
Vitamin D deficiency can lead to osteoporosis in adults or rickets in children.
Too much vitamin D can make the intestines absorb too much calcium. This may cause high levels of calcium in the blood. High blood calcium can lead to calcium deposits in soft tissues such as the heart and lungs. This can reduce their ability to function.
Kidney stones, vomiting, and muscle weakness may also occur if you have too much vitamin D.

Recommendations
How To Get Enough Vitamin D
There are 3 ways for adults to ensure adequate levels of vitamin D:
• regularly receive midday sun exposure in the late spring, summer, and early fall, exposing as much of the skin as possible for 20–30 minutes (being careful to never burn). (Those with dark skin will need longer exposure time — up to six times longer.)
• regularly use a sun bed (avoiding sunburn) during the colder months.
• take 5,000 IU per day for 2–3 months, then obtain a 25-hydroxyvitamin D test. Adjust your dosage so that blood levels are between 50–80 ng/mL (or 125–200 nM/L) year-round.
Vitamin D is also known as the “sunshine vitamin” because the body manufactures the vitamin after being exposed to sunshine. Ten to 15 minutes of sunshine 3 times weekly is enough to produce the body’s requirement of vitamin D. However, many people living in sunny climates still do not make enough vitamin D and need more from their diet or supplementation.
The Food and Nutrition Board at the Institute of Medicine recommends the following dietary intake for vitamin D as cholecalciferol. (One microgram of cholecalciferol is the same as 40 IU of vitamin D.)
Infants
• 0 – 6 months: 5 micrograms per day (mcg/day)
• 7 – 12 months: 5 mcg/day
Children
• 1 – 13 years: 5 mcg/day
Adolescents and Adults
• Males and Females age 14 to 50: 5 mcg/day
• Males and Females age 51 to 70: 10 mcg/day
• Males and Females age over 70: 15 mcg/day
Specific recommendations for each vitamin depend on age, gender, and other factors (such as pregnancy). In general, those over age 50 need higher amounts of vitamin D than younger persons. Ask your health care provider which amount is best for you.
Vitamin D’s Co-factors
Vitamin D has co-factors that the body needs in order to utilize vitamin D properly. They are:
• magnesium
• zinc
• vitamin K2
• boron
• a tiny amount of vitamin A
Magnesium is the most important of these co-factors. In fact, it is common for rising vitamin D levels to exacerbate an underlying magnesium deficiency. If one is having problems supplementing with vitamin D, a magnesium deficiency could be the reason why.
Alternative Names
Cholecalciferol
Thank you and references
http://www.nlm.nih.gov/medlineplus/ency/article/002405.htm
http://www.mayoclinic.com
http://www.vitamindcouncil.org/
http://www.medicalnewstoday.com\

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