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Vitamin D, It's More Than Sunshine
Are you getting enough of the "sunshine" vitamin? Probably not; as many as 50%-75% of Americans may not be getting enough vitamin D for optimal health, according to researchers. New research has expanded our knowledge of the role vitamin D plays in promoting overall health and is becoming an increasingly important factor in a healthful diet. Vitamin D deficiency is recognized as a pandemic in this country due to declining intakes and reduced sunlight exposure. The recommendation for the avoidance of all sun exposure has put the world's population at risk of vitamin D deficiency.
What is Vitamin D?
Vitamin D helps the body absorb calcium and keeps the right amount of calcium and phosphorus in the blood. Vitamin D is synthesized in the skin and then converted to its active form by the liver and then the kidney. Vitamin D is the only vitamin the body makes itself in any significant amounts. Without enough vitamin D, you can't form enough of the hormone calcitriol (active form). If there is not enough vitamin D, the body must then take calcium from its storage in the skeleton, which weakens existing bone and prevents the formation of strong, new bone. Vitamin D behaves like a hormone in the body, relaying chemical messages; something no other vitamin does. The two major forms of vitamin D are D2 (ergocalciferol) and D3 (cholecalciferol). Small amounts of vitamin D2 are obtained from foods of plant origin whereas vitamin D3 is obtained from foods of animal origin and from ultraviolet light-stimulated conversion in the skin.
Where do we get Vitamin D?
Vitamin D is obtained in three ways: through the skin, from the diet, and from dietary supplements. It is formed naturally by the body after exposure to sunlight. Ten to fifteen minutes in the sun without sunscreen a few times a week is plenty for many people to manufacture and store all of the vitamin D they need. It is recommended that sun exposure be obtained on off peak hours, not during the 10am to 2pm time frame during the day and during an ultraviolet (UV) index of less than 6. Controversy remains as to the direct exposure to sunlight in providing adequate vitamin D. The National Council on Skin Cancer Prevention encourages Americans to obtain vitamin D through dietary sources and supplements and not through intentional exposure to ultraviolet radiation, since UV radiation is a known carcinogen.
Few foods are naturally vitamin D-rich. One of the richest dietary sources of the nutrient is D-fortified milk and D-fortified foods; oily fish, such as salmon, tuna, mackerel and sardines naturally contain D. Egg yolks, vitamin D-fortified yogurts and cheeses, breakfast bars and soy beverages are also good choices. Others foods such as orange juice, margarine, and breakfast cereals may be fortified with vitamin D as well.
Supplementation is another way to increase vitamin D levels. Multivitamin supplements provide between 200 and 400 IU per tablet whereas individual supplements can provide up to 1,000 IU of vitamin D. It is best to discuss with your health care provider before starting any supplement intake.
How much do we need?
The Institute of Medicine (IOM) for the National Academy of Sciences issued a report and concluded that it was not possible to determine a recommended dietary allowance (RDA) for vitamin D but would recommend as adequate intake (AI). Based on their literature and assuming some sun exposure, an AI for ages 0-50 years was set at 200 IU (international units)/day. The IOM set the AI for adults 51-70 years as 400 IU/day and for adults>71 years, 600 IU/day. Aging is associated with decreased concentrations of vitamin D. These recommendations, however, were set to assure adequate intakes of the vitamin primarily for bone health. As we learn more about vitamin D and its many health benefits, experts agree much higher levels will soon be established for optimal health benefits. Some documented researchers have suggested as much as 2,000 IU per day.
What are the consequences of vitamin D deficiency?
Vitamin D deficiency in children causes rickets (bones do not harden) and growth retardation. In adults, deficiency will precipitate and exacerbate osteopenia, osteoporosis (porous bone), and fractures. Research has shown vitamin D deficiency has been associated with increased risk of common cancer mortality (breast, colorectal, prostate, pancreas, and esophagus), autoimmune diseases (multiple sclerosis and rheumatoid arthritis), hypertension, and infectious diseases. Muscle weakness, increase in body sway, and an increased risk of falling have also been associated with vitamin D deficiency.
How is vitamin D tested?
The best method for determining a person's vitamin D status is to measure a 25(OH)D concentration. This is a simple blood test. It reflects how much vitamin D is produced cutaneously and that obtained from food and supplements. Levels of 25(OH)D concentration vary with exposure to sunlight and do not indicate the amount of vitamin D stored in body tissues. Research indicates a 25(OH)D concentration <30ng/mL is an indication of vitamin D insufficiency, while a concentration <20ng/mL is an indication of vitamin D deficiency. A level above 30ng/mL is considered by some experts as desirable for overall health and disease prevention; however a recent governmental-sponsored expert panel concluded that insufficient data are available to support higher levels.
Are there interactions of vitamin D with medications?
Vitamin D supplements can interact with several types of medications. Discuss with your healthcare provider and/or pharmacist before taking any supplements. Corticosteroid medications such as prednisone can reduce calcium absorption and impair vitamin D metabolism. This can contribute to lose of bone and the development of osteoporosis with long term use. Other medications such as weight-loss drugs (Xenical, Alli) and cholesterol-lowering drugs (Questran, LoCholest, and Prevalite) can reduce the absorption of vitamin D. Anti-seizure medications (Dilantin) used to prevent seizures, reduce calcium absorption as well.
What are the benefits of vitamin D?
There are many benefits to adequate levels of vitamin D. According to the Johns Hopkins Medicine Health Alert, studies suggest that there are heart benefits of vitamin D that include blood pressure regulation, heart attack, stroke, and heart failure reductions as well as helping to reduce inflammation in the arteries. Epidemiological documentation by the American Journal of Clinical Nutrition shows that increasing vitamin D decreases the risk of developing many chronic diseases such as Type 1 diabetes mellitus, rheumatoid arthritis, multiple sclerosis, Crohn's disease and colon cancer. Active vitamin D boosts the immune system and is effective in maintaining essential blood levels of calcium to maintain optimal functioning bone health.
Last updated: 2009/09/22