Vitamin D - The Sunshine Vitamin

Introducing Vitamin D - Sun Shine Vitamin

Vitamin D, cholecalciferol, is a fat-soluble vitamin. It is found in food, but also can be made in your body after exposure to ultraviolet rays from the sun. It is one vitamin that you can directly get it from the sun light, for free! Sounds nice, eh? Vitamin D exists in several forms, each with a different activity. Some forms are relatively inactive in the body, and have limited ability to function as a vitamin. The liver and kidney help convert vitamin D to its active hormone form.

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Why Vitamin D?

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. It promotes bone mineralization in concert with a number of other vitamins, minerals, and hormones. Without vitamin D, bones can become thin, brittle, soft, or misshapen. Vitamin D prevents rickets in children and osteomalacia in adults, which are skeletal diseases that result in defects that weaken bones.

Vitamin D and Calcium Metabolism

Vitamin D is crucial in calcium metabolism. Maintenance of blood calcium levels within a narrow range is vital for normal functioning of the nervous system, as well as for bone growth, and maintenance of bone density. This tight regulation is accomplished through a complex system, sometimes called the vitamin D endocrine system, because the active form of vitamin D3 has a mechanism of action similar to some hormones, for example, thyroid hormone.

Vitamin D and Calcidiol

Once vitamin D enters the circulation from either the diet or the skin, it is bound to the vitamin D-binding protein and transported to the liver. In the liver, vitamin D is hydroxylated on carbon molecule #25 to form 25-hydroxyvitamin D, also known as calcidiol. Though the synthesis of calcidiol is controlled in the liver, increased exposure to sunlight or increased intake of vitamin D3 results in increased blood levels of calcidiol, making it a useful indicator of vitamin D nutritional status.

The physiologic effects of calcitriol require proteins known as receptors. Calcitriol enters the cell and interacts with a vitamin D receptor (VDR) in the nucleus to form a complex. The calcitriol/VDR complex combines with another receptor, the retinoic acid X receptor (RXR), to form a heterodimer, which can then interact with small portions of DNA known as vitamin D responsive elements (VDRE). The interaction of a VDR/RXR heterodimer with a VDRE results in a change in the rate of transcription of a nearby gene. In this manner, the the activity of vitamin D-dependent calcium transporters in the small intestine, osteoblasts in bone, and the 1-hydroxylase enzyme in the kidneys may be increased.

Cells that are dividing rapidly are said to be proliferating. Cell proliferation can be observed during growth and wound healing (regeneration). Differentiation results in the specialization of cells for specific functions, such as those of a nerve cell. In general, differentiation of cells leads to a decrease in proliferation. Psoriasis is a disease characterized by the proliferation of skin cells called keratinocytes. The identification of VDR in keratinocytes led to the use of creams containing analogs of calcitriol in the treatment of severe cases of psoriasis.

Vitamin D receptors (VDR) have been identified in cells that play a critical role in the immune system. Specialized white blood cells, known as T-lymphocytes or T-cells, are involved in the recognition of foreign pathogens known as antigens, and coordinating the immune response. Some diseases are associated with immune responses to inappropriate antigens. For example, autoimmune diseases occur when an immune response is mounted to an antigen belonging to oneself rather than a foreign antigen, and allergies occur when the antigen is an innocuous foreign substance. Immune responses that are mediated by T-cells can be inhibited by large doses of calcitriol. However, a deficiency of vitamin D also interferes with T-cell mediated immunity. The presence of VDR in T-cells suggests that vitamin D plays a role in the function and/or the development of T-cells. Pharmacologic doses of calcitriol have had beneficial effects in animal models of several autoimmune diseases, mediated by T-cells.

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Food High in Vitamin D and Who are likely to be Deficient

Food high in vitamin D is limited compare to the food high in other vitamins. The rich food sources for vitamin D include the following categories:
Cod-liver Oil, Halibut-liver Oil, Herring, Salmon, Sardines, Tuna.

As you may see from the above, the food source for vitamin D is very limited compare to other vitamins. But the good news is with enough sun light exposure, your body can produce the rest of vitamin D that is needed. However, once again, an alarm bell is sounded for the people who are greater than age 50. Due to the over all nutrient absorbtion is weakening (The ability of skin to convert vitamin D to its active form decreases as we age; the kidneys, which help convert vitamin D to its active form, sometimes do not work as well when people age), the elderly are at a higher risk of developing vitamin D deficiency. Therefore, some older people may need vitamin D from a supplement.

Besides the elders, the following people are also suggested to take some vitamin D supplements:
- Children who live in sunshine deficient areas
- Adults with limited sun exposure (for example, people who are institutionalized, use sunscreen or live in an area of limited sun exposure)
- Anyone with inadequate caloric or nutritional dietary intake or increased nutritional requirements.
- Pregnant or breastfeeding women
- Those who abuse alcohol or other drugs
- People with a chronic wasting illness
- Those under excess stress for long periods
- Anyone who has recently undergone surgery
- Those with a portion of the gastrointestinal tract surgically removed
- People with recent burns or injuries
- Dark-skinned individuals
- Breastfed babies
- Vegetarians
- Anyone with a liver impairment such as cirrhosis or obstructive jaundice

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Vitamin D Deficiency Symptoms

A deficiency of vitamin D can occur when dietary intake of vitamin D is inadequate, when there is limited exposure to sunlight, when the kidney cannot convert vitamin D to its active form, or when someone cannot adequately absorb vitamin D from the gastrointestinal tract .

The classic vitamin D deficiency diseases are rickets and osteomalacia. In children, vitamin D deficiency causes rickets, which results in skeletal deformities. Rickets results in the failure of bone to mineralize. Children have rapidly growing bones which are most severely affected by rickets. The growth plates of bones continue to enlarge, but in the absence of adequate mineralization, weight-bearing limbs (arms and legs) become bowed. In infants, rickets may result in soft spots in the skull, and the rib cage may become deformed due to the pulling action of the diaphragm. The treatment of rickets includes vitamin D or calcitriol supplementation, a diet that provides adequate calcium and phosphorus, and a plan for the prevention of future vitamin D deficiency. Click HERE for essential vitamin D supplements and save.

In adults, vitamin D deficiency can lead to osteomalacia, which results in muscular weakness in addition to weak bones. Although adult bones are no longer growing, they are in a constant state of turnover. Bone is a dynamic tissue that is continually remodeling in response to stress. The remodeling process involves the demineralization and remineralization of bone through the action of bone cells called osteoclasts and osteoblasts, respectively. In adults with prolonged vitamin D deficiency, the collagenous bone matrix is preserved but bone mineral is progressively lost as a result of normal bone turnover, resulting in bone pain (in ribs, lower spine, pelvis and legs), muscle weakness and osteomalacia (soft bones).

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Recent Studies on Vtiamin C and Your Health

Vitamin D and osteoporosis
It is estimated that over 25 million adults in the United States have, or are at risk of developing osteoporosis. Osteoporosis is a disease characterized by fragile bones. It results in increased risk of bone fractures. Having normal storage levels of vitamin D in your body helps keep your bones strong and may help prevent osteoporosis in elderly, non-ambulatory individuals, in post-menopausal women, and in individuals on chronic steroid therapy.

Researchers know that normal bone is constantly being remodeled (broken down and rebuilt). During menopause, the balance between these two systems is upset, resulting in more bone being broken down (resorbed) than rebuilt. Estrogen replacement, which limits symptoms of menopause, can help slow down the development of osteoporosis by stimulating the activity of cells that rebuild bone.

Vitamin D deficiency, which occurs more often in post-menopausal women and older Americans, has been associated with greater incidence of hip fractures. A greater vitamin D intake from diet and supplements has been associated with less bone loss in older women. Since bone loss increases the risk of fractures, vitamin D supplementation may help prevent fractures resulting from osteoporosis.

In a group of women with osteoporosis hospitalized for hip fractures, 50 percent were found to have signs of vitamin D deficiency. Treatment of vitamin D deficiency can result in decreased incidence of hip fractures, and daily supplementation with 20 mcg (800 IU) of vitamin D may reduce the risk of osteoporotic fractures in elderly populations with low blood levels of vitamin D. Your physician will discuss your need for vitamin D supplementation as part of an overall plan to prevent and/or treat osteoporosis when indicated.

Vitamin D and cancer
Laboratory, animal, and epidemiologic evidence suggest that vitamin D may be protective against some cancers. Some dietary surveys have associated increased intake of dairy foods with decreased incidence of colon cancer. Another dietary survey associated a higher calcium and vitamin D intake with a lower incidence of colon cancer. Well-designed clinical trials need to be conducted to determine whether vitamin D deficiency increases cancer risk, or if an increased intake of vitamin D is protective against some cancers. Until such trials are conducted, it is premature to advise anyone to take vitamin D supplements to prevent cancer.

Vitamin D and steroids
Corticosteroid medications are often prescribed to reduce inflammation from a variety of medical problems. These medicines may be essential for a person’s medical treatment, but they have potential side effects, including decreased calcium absorption. There is some evidence that steroids may also impair vitamin D metabolism, further contributing to the loss of bone and development of osteoporosis associated with steroid medications. For these reasons, individuals on chronic steroid therapy should consult with their physician or registered dietitian about the need to increase vitamin D intake through diet and/or dietary supplements.

Vitamin D and Alzheimer’s Disease
Adults with Alzheimer’s disease have increased risk of hip fractures. This may be because many Alzheimer’s patients are homebound, and frequently sunlight deprived. Alzheimer’s disease is more prevalent in older populations, so the fact that the ability of skin to convert vitamin D to its active form decreases as we age also may contribute to increased risk of hip fractures in this group. One study of women with Alzheimer’s disease found that decreased bone mineral density was associated with a low intake of vitamin D and inadequate sunlight exposure. Physicians evaluate the need for vitamin D supplementation as part of an overall treatment plan for adults with Alzheimer’s disease.

Vitamin D and Autoimmune Disease
Insulin-dependent diabetes mellitus (IDDM), multiple sclerosis (MS), and rheumatoid arthritis (RA) are each examples of autoimmune disease. In IDDM, insulin producing beta (b)-cells of the pancreas are the target of the inappropriate immune response. In MS and RA, the targets are the myelin producing cells of the central nervous system and the collagen producing cells of the joints, respectively. The autoimmune responses are mediated by T-lymphocytes (T-cells). The biologically active form of vitamin D, calcitriol, has been found to modulate T-cell responses, such that the autoimmune responses are diminished. Treatment with calcitriol has had beneficial effects in animal models of IDDM, MS, and RA. In humans, increased incidence of IDDM, MS, and RA are found in geographic regions with low supplies of vitamin D (low sunlight exposure and low dietary intake). Presently, vitamin D and calcium supplementation are advocated for individuals at risk of osteoporosis from corticosteroid regimens prescribed to treat autoimmune diseases. Although the use of vitamin D and vitamin D analogs in the therapy of certain autoimmune diseases holds promise, further research is required before their safety and efficacy can be determined.

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Editors' summary on Vitamin D

Vitamin D is a fat-soluble vitamin. You may have it either from dietary or from sunlight absorbtion through skin. It absorbs and uses calcium and phosphorus to make bone. It is essential for normal growth and development. The elders are easy to be deficient in vitamin D.

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