Hecapedia - Vitamin D

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Vitamin D

ÿþ Vitamin D is a fat soluble vitamin that is found in food and can also be made in your body after exposure to ultraviolet (UV) rays from the sun. Sunshine is a significant source of vitamin D because UV rays from sunlight trigger vitamin D synthesis in the skin. Vitamin D exists in several forms, each with a different level of activity. Calciferol is the most active form of vitamin D. Other forms are relatively inactive in the body. The liver and kidney help convert vitamin D to its active hormone form. Once vitamin D is produced in the skin or consumed in food, it requires chemical conversion in the liver and kidney to form 1,25 dihydroxyvitamin D, the physiologically active form of vitamin D. Active vitamin D functions as a hormone because it sends a message to the intestines to increase the absorption of calcium and phosphorus. The major biologic function of vitamin D is to maintain normal blood levels of calcium and phosphorus. By promoting calcium absorption, vitamin D helps to form and maintain strong bones. Vitamin D also works in concert with a number of other vitamins, minerals, and hormones to promote bone mineralization. Without vitamin D, bones can become thin, brittle, or misshapen. Vitamin D sufficiency prevents rickets in children and osteomalacia in adults, two forms of skeletal diseases that weaken bones. Sources of vitamin D Food Sources Fortified foods are common sources of vitamin D Selected food sources of vitamin D <table border= 1 width=90% align=center> <tr> <td align=center>Food</td> <td align=center>International Units(IU) per serving</td> <td align=center>Percent DV*</td> </tr> <tr> <td cellspacing="2" cellpadding="4">   Cod liver oil, 1 Tablespoon</td> <td cellspacing="2" cellpadding="4">  1,360</td> <td cellspacing="2" cellpadding="4">  340</td> </tr> <tr> <td cellspacing="2" cellpadding="4">  Salmon, cooked, 3½ ounces</td> <td cellspacing="2" cellpadding="4">  360</td> <td cellspacing="2" cellpadding="4">  90</td> </tr> <tr> <td cellspacing="2" cellpadding="4">  Mackerel, cooked, 3½ ounces</td> <td cellspacing="2" cellpadding="4">  345</td> <td cellspacing="2" cellpadding="4">  90</td> </tr> <tr> <td cellspacing="2" cellpadding="4">  Tuna fish, canned in oil, 3 ounces</td> <td cellspacing="2" cellpadding="4">  200</td> <td cellspacing="2" cellpadding="4">  50</td> </tr> <tr> <td cellspacing="2" cellpadding="4">  Sardines, canned in oil, drained, 1¾ ounces</td> <td cellspacing="2" cellpadding="4">  250</td> <td cellspacing="2" cellpadding="4">  70</td> </tr> <tr> <td cellspacing="2" cellpadding="4">  Milk, nonfat, reduced fat, and whole, vitamin D fortified, 1 cup</td> <td cellspacing="2" cellpadding="4">  98</td> <td cellspacing="2" cellpadding="4">  25</td> </tr> <tr> <td cellspacing="2" cellpadding="4">  Margarine, fortified, 1 Tablespoon</td> <td cellspacing="2" cellpadding="4">  60</td> <td cellspacing="2" cellpadding="4">  15</td> </tr> <tr> <td cellspacing="2" cellpadding="4">  Pudding, prepared from mix and made with vitamin D fortified milk, ½ cup</td> <td cellspacing="2" cellpadding="4">  50</td> <td cellspacing="2" cellpadding="4">  10</td> </tr> <tr> <td cellspacing="2" cellpadding="4">  Ready-to-eat cereals fortified with 10% of the DV for vitamin D, ¾ cup to 1 cup servings (servings vary according to the brand)</td> <td cellspacing="2" cellpadding="4">  40</td> <td cellspacing="2" cellpadding="4">  10</td> </tr> <tr> <td cellspacing="2" cellpadding="4">  Egg, 1 whole (vitamin D is found in egg yolk)</td> <td cellspacing="2" cellpadding="4">  20</td> <td cellspacing="2" cellpadding="4">  6</td> </tr> <tr> <td cellspacing="2" cellpadding="4">  Liver, beef, cooked, 3½ ounces</td> <td cellspacing="2" cellpadding="4">  15</td> <td cellspacing="2" cellpadding="4">  4</td> </tr> <tr> <td cellspacing="2" cellpadding="4">  Cheese, Swiss, 1 ounce</td> <td cellspacing="2" cellpadding="4">  12</td> <td cellspacing="2" cellpadding="4">  4</td> </tr> </table> *DV = Daily Value. Sun exposure Sun exposure is perhaps the most important source of vitamin D because exposure to sunlight provides most humans with their vitamin D requirement. UV rays from the sun trigger vitamin D synthesis in skin. Season, geographic latitude, time of day, cloud cover, smog, and sunscreen affect UV ray exposure and vitamin D synthesis Complete cloud cover halves the energy of UV rays, and shade reduces it by 60%. Industrial pollution, which increases shade, also decreases sun exposure and may contribute to the development of rickets in individuals with insufficient dietary intake of vitamin D. Sunscreens with a sun protection factor (SPF) of 8 or greater will block UV rays that produce vitamin D, but it is still important to routinely use sunscreen to help prevent skin cancer and other negative consequences of excessive sun exposure. An initial exposure to sunlight (10 -15 minutes) allows adequate time for Vitamin D synthesis and should be followed by application of a sunscreen with an SPF of at least 15 to protect the skin. Ten to fifteen minutes of sun exposure at least two times per week to the face, arms, hands, or back without sunscreen is usually sufficient to provide adequate vitamin D. It is very important for individuals with limited sun exposure to include good sources of vitamin D in their diet. Recommended intake for vitamin D Adequate Intake for vitamin D for infants, children, and adults <table border= 1 width=90% align=center> <tr> <td align=center>Age</td> <td align=center>Children (¼g/day) </td> <td align=center>Men(¼g/day)</td> <td align=center>Women(¼g/day)</td> <td align=center>Pregnancy(¼g/day)</td> <td align=center>Lactation(¼g/day)</td> </tr> <tr> <td cellspacing="2" cellpadding="4">   Birth to 13 years</td> <td cellspacing="2" cellpadding="4">  5(=200 IU)</td> <td cellspacing="2" cellpadding="4">  </td> <td cellspacing="2" cellpadding="4">  </td> <td cellspacing="2" cellpadding="4">   </td> <td cellspacing="2" cellpadding="4">  </td> </tr> <tr> <td cellspacing="2" cellpadding="4">  14 to 18 years</td> <td cellspacing="2" cellpadding="4">  </td> <td cellspacing="2" cellpadding="4">  5(=200 IU)</td> <td cellspacing="2" cellpadding="4">   5(=200 IU)</td> <td cellspacing="2" cellpadding="4">  5(=200 IU)</td> <td cellspacing="2" cellpadding="4">  5(=200 IU)</td> </tr> <tr> <td cellspacing="2" cellpadding="4">  19 to 50 years</td> <td cellspacing="2" cellpadding="4">  </td> <td cellspacing="2" cellpadding="4">  5(=200 IU)</td> <td cellspacing="2" cellpadding="4">   5(=200 IU)</td> <td cellspacing="2" cellpadding="4">  5(=200 IU)</td> <td cellspacing="2" cellpadding="4">  5(=200 IU)</td> </tr> <tr> <td cellspacing="2" cellpadding="4">  51 to 70 years</td> <td cellspacing="2" cellpadding="4">  </td> <td cellspacing="2" cellpadding="4">  10(=400 IU)</td> <td cellspacing="2" cellpadding="4">  10(=400 IU)</td> <td cellspacing="2" cellpadding="4">   </td> <td cellspacing="2" cellpadding="4">  </td> </tr> <tr> <td cellspacing="2" cellpadding="4">  71+ years</td> <td cellspacing="2" cellpadding="4">  </td> <td cellspacing="2" cellpadding="4">  15 (=600 IU)</td> <td cellspacing="2" cellpadding="4">   15(=600 IU)</td> <td cellspacing="2" cellpadding="4">  </td> <td cellspacing="2" cellpadding="4">  </td> </tr> </table> Vitamin D deficiency Nutrient deficiencies are usually the result of dietary inadequacy, impaired absorption and utilization, increased requirement, or increased excretion (loss). A deficiency of vitamin D can occur : <ul> <li> when usual intake is below recommended levels </li> <li> when there is limited exposure to sunlight </li> <li> when the kidney cannot convert vitamin D to its active hormone form </li> <li> when someone cannot adequately absorb vitamin D from the digestive tract </li> </ul> Vitamin D deficient diets are associated with milk allergy, lactose intolerance, and strict vegetarianism. Infants fed only breast milk also receive insufficient amounts of vitamin D unless they also receive appropriate levels of vitamin D supplementation. The classic vitamin D deficiency diseases are rickets and osteomalacia. In children, vitamin D deficiency causes rickets. Rickets is a bone disease characterized by a failure to properly mineralize bone tissue. Rickets results in soft bones and skeletal deformities. The most common causes of rickets are vitamin D deficiency from a vitamin D deficient diet, lack of sunlight, or both. Prolonged exclusive breastfeeding without vitamin D supplementation is one of the most significant causes of the reemergence of rickets. Additional causes include extensive use of sunscreens and increased use of day-care, resulting in decreased outdoor activity and sun exposure among children. In adults, vitamin D deficiency can lead to osteomalacia, which results in muscular weakness in addition to weak bones. Symptoms of bone pain and muscle weakness may indicate vitamin D deficiency, but symptoms may be subtle and go undetected in the initial stages. A deficiency is accurately diagnosed by measuring the concentration of a specific form of vitamin D in blood. Who may need extra vitamin D to prevent a deficiency? It can be difficult to obtain enough vitamin D from natural food sources. For many people, consuming vitamin D fortified foods and adequate sunlight exposure are essential for maintaining a healthy vitamin D status. In some groups, dietary supplements may be needed to meet the daily need for vitamin D. Infants who are exclusively breastfed In infants, vitamin D requirements cannot be met by human (breast) milk alone. Sunlight is a potential source of vitamin D for infants, but it is advised that infants be kept out of direct sunlight and wear protective clothing and sunscreen when exposed to sunlight. It is recommended a daily supplement of 200 IU vitamin D for breastfed infants beginning within the first 2 months of life unless they are weaned to receive at least 500 ml (about 2 cups) per day of vitamin D-fortified formula. Children and adolescents who are not routinely exposed to sunlight and do not consume at least 2, 8-fluid ounce servings of vitamin D-fortified milk per day are also at higher risk of vitamin D deficiency and may need a dietary supplement containing 200 IU vitamin D. Older adults people age 50 and older are believed to be at increased risk of developing vitamin D deficiency. As people age, skin cannot synthesize vitamin D as efficiently and the kidney is less able to convert vitamin D to its active hormone form. It is estimated that as many as 30% to 40% of older adults with hip fractures are vitamin D insufficient. Therefore, older adults may benefit from supplemental vitamin D. Persons with greater skin melanin content Melanin is the pigment that gives skin its color. Greater amounts of melanin result in darker skin. The high melanin content in darker skin reduces the skin's ability to produce vitamin D from sunlight. Individuals with darkly pigmented skin who are unable to get adequate sun exposure and/or consume recommended amounts of vitamin D may benefit from a vitamin D supplement. Persons with fat malabsorption As a fat soluble vitamin, vitamin D requires some dietary fat for absorption. Individuals who have a reduced ability to absorb dietary fat may require vitamin D supplements. Symptoms of fat malabsorption include diarrhea and oily stools. Fat malabsorption is associated with a variety of medical conditions: Pancreatic enzyme deficiency is characterized by insufficient secretion of pancreatic enzymes. Pancreatic enzymes are essential for fat absorption, and a deficiency of these enzymes can result in fat malabsorption. Crohn's Disease is an inflammatory bowel disease that affects the small intestines. People with Crohn's disease often experience diarrhea and fat malabsorption. Cystic Fibrosis (CF) is a hereditary disorder that causes the body to secrete a thick, sticky mucus. This mucus clogs the pancreas and lungs. People with CF often experience fat malabsorption. Sprue, often referred to as Celiac Disease (CD), is a genetic disorder. People with CD are intolerant to a protein called gluten. In CD, gluten can trigger damage to the small intestines, where most nutrient absorption occurs. People with CD often experience fat malabsorption. They need to follow a gluten free diet to avoid malabsorption and other symptoms of CD. Liver disease includes a wide variety of disorders that impair liver function. Some people with liver disease experience fat malabsorption. Surgical removal of part or all of the stomach or intestines can impair digestion and absorption of many nutrients. Fat malabsorption can occur after this type of surgery. Some current issues and controversies about vitamin D Vitamin D and osteoporosis: Osteoporosis is a disease characterized by fragile bones, and it significantly increases the risk of bone fractures. Osteoporosis is most often associated with inadequate calcium intake. However, a deficiency of vitamin D also contributes to osteoporosis by reducing calcium absorption. While rickets and osteomalacia are extreme examples of vitamin D deficiency, osteopororsis is an example of a long-term effect of vitamin D insufficiency. Adequate storage levels of vitamin D help keep bones strong and may help prevent osteoporosis in older adults, in non-ambulatory individuals (those who have difficulty walking and exercising), in post-menopausal women, and in individuals on chronic steroid therapy. Researchers know that normal bone is constantly being remodeled, a process that describes the breakdown and rebuilding of bone. During menopause, the balance between these two systems changes, resulting in more bone being broken down or resorbed than rebuilt. Hormone therapy (HT) with sex hormones such as estrogen and progesterone may delay the onset of osteoporosis. Daily supplementation with 20 ¼g (800 IU) of vitamin D may reduce the risk of osteoporotic fractures in elderly populations with low blood levels of vitamin D. Vitamin D and cancer: Laboratory, animal, and epidemiologic evidence suggests that vitamin D may be protective against some cancers. Epidemiologic studies suggest that a higher dietary intake of calcium and vitamin D, and/or sunlight-induced vitamin D synthesis, correlates with lower incidence of cancer. In fact, for over 60 years researchers have observed an inverse association between sun exposure and cancer mortality. The inverse relationship between higher vitamin D levels in blood and lower cancer risk in humans is best documented for colon and colorectal cancers. Additional 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 for cancer prevention. Vitamin D and steroids: Corticosteroid medications such as prednisone are often prescribed to reduce inflammation from a variety of medical problems. These medicines may be essential for 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 long term use of steroid medications. One study demonstrated that patients who received 0.25 ¼g of active vitamin D and 1000 mg calcium per day in addition to corticosteroid therapy after a kidney transplant avoided rapid bone loss commonly associated with post-transplant therapy. For these reasons, individuals on chronic steroid therapy should consult with a qualified health care professional about the need to increase vitamin D intake through diet and/or dietary supplements. Vitamin D and Alzheimer's disease: Alzheimer's disease is associated with an increased risk of hip fractures. This may be because many Alzheimer's patients are homebound, frequently sunlight deprived, and older. With aging, less vitamin D is converted to its active form. 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 should evaluate the need for vitamin D supplementation as part of an overall treatment plan for adults with Alzheimer's disease. Vitamin D and caffeine: High caffeine intake may accelerate bone loss. Caffeine may inhibit vitamin D receptors, thus limiting absorption of vitamin D and decreasing bone mineral density. A study found that elderly postmenopausal women who consumed more than 300 milligrams per day of caffeine (which is equivalent to approximately 18 oz of caffeinated coffee) lost more bone in the spine than women who consumed less than 300 milligrams per day. However, there is also evidence that increasing calcium intake (by, for example, adding milk to coffee) can counteract any potential negative effect that caffeine may have on bone loss. More evidence is needed before health professionals can confidently advise adults to decrease caffeine intake as a means of preventing osteoporosis. Health risks of too much vitamin D Vitamin D toxicity can cause nausea, vomiting, poor appetite, constipation, weakness, and weight loss. It can also raise blood levels of calcium, causing mental status changes such as confusion. High blood levels of calcium also can cause heart rhythm abnormalities. Calcinosis, the deposition of calcium and phosphate in the body's soft tissues such as the kidney, can also be caused by vitamin D toxicity. Sun exposure is unlikely to result in vitamin D toxicity. Diet is also unlikely to cause vitamin D toxicity, unless large amounts of cod liver oil are consumed. Vitamin D toxicity is much more likely to occur from high intakes of vitamin D in supplements. Tolerable Upper Intake Levels for vitamin D for infants, children, and adults <table border= 1 width=90% align=center> <tr> <td align=center>Age</td> <td align=center>Men(¼g/day)</td> <td align=center>Women(¼g/day)</td> <td align=center>Pregnancy(¼g/day)</td> <td align=center>Lactation(¼g/day)</td> </tr> <tr> <td cellspacing="2" cellpadding="4">   0 to 12 months</td> <td cellspacing="2" cellpadding="4">  25(=1,000 IU)</td> <td cellspacing="2" cellpadding="4">  25(=1,000 IU)</td> <td cellspacing="2" cellpadding="4">   </td> <td cellspacing="2" cellpadding="4">  </td> </tr> <tr> <td cellspacing="2" cellpadding="4">  1 to 13 years</td> <td cellspacing="2" cellpadding="4">  50(=2,000 IU</td> <td cellspacing="2" cellpadding="4">  50(=2,000 IU</td> <td cellspacing="2" cellpadding="4">   </td> <td cellspacing="2" cellpadding="4">  </td> </tr> <tr> <td cellspacing="2" cellpadding="4">  14 to 18 years</td> <td cellspacing="2" cellpadding="4">  50(=2,000 IU</td> <td cellspacing="2" cellpadding="4">  50(=2,000 IU</td> <td cellspacing="2" cellpadding="4">   50(=2,000 IU</td> <td cellspacing="2" cellpadding="4">  50(=2,000 IU</td> </tr> <tr> <td cellspacing="2" cellpadding="4">  19+ years</td> <td cellspacing="2" cellpadding="4">  50 (=2,000 IU)</td> <td cellspacing="2" cellpadding="4">  50 (=2,000 IU)</td> <td cellspacing="2" cellpadding="4">   50 (=2,000 IU)</td> <td cellspacing="2" cellpadding="4">  50 (=2,000 IU)</td> </tr> </table>

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Vitamin D