Article: Why this Vitamin is D Nutrient of the Year -
02 Aug 2010
Vitamin D is shaping up to be the nutrient of the year if not the decade. It is, of course, best known for the key role it plays in bone health without it calcium cannot be absorbed, and the risk of osteoporosis and fractures increases. But evidence that links vitamin D deficiency with many other health problems continues to accumulate. In the past year alone, higher vitamin D levels have been linked with a reduced risk of fracture, lower susceptibility to colds and flu, better brain function, and a lower percentage of body fat in women.
Yet, despite growing evidence that vitamin D makes a vital contribution to good health as we age, itís thought that more than 1/10 of older adults now have vitamin D levels associated with higher risks for various diseases, and that few have optimum levels.
Since there are vitamin D receptors all over the body in the muscles, joints, brain, and other organs low vitamin D levels have a systemic effect (they are also linked with colon cancer, breast cancer, a weakened immune system, and poorer brain function).
WHAT RESEARCH SHOWS
The picture of vitamin Dís health benefits beyond bones has been drawn mainly from epidemiologic and observational investigations. The findings of such studies can suggest correlations between disease risk and certain factors sun exposure or blood levels of vitamin D, for example but they donít prove cause and effect. More trials are needed to elucidate vitamin Dís benefits and risks at different doses and in different populations.
Most experts, however, have found the evidence strong enough to raise the recommended daily intake of vitamin D to 800 IU (international units), a level high enough to prevent deficiency even in people who get little or none of the vitamin through sunlight. That level can help strengthen bones and muscles, but whether it can ward off chronic disease is less clear. With that in mind, hereís a rundown of the areas in which vitamin D shows disease-fighting promise.
ē Bone health. The bone-building minerals calcium and phosphorus rely on vitamin D for absorption. A review of 167 studies found that people who got at least 700 IU of the vitamin and took calcium pills had denser bones and fewer fractures than those who didnít take the vitamin D supplements.
ē Muscular strength. Studies have shown that deficiency in the vitamin decreases muscular strength and performance.
ē Cancer. Vitamin D helps regulate cell growth and so may inhibit the formation or spread of cancer cells. Some population-based studies have linked deficiency of the vitamin to an increased risk of breast, colon, and prostate cancer as well as higher mortalities from those cancers.
ē Cardiovascular disease. Low levels of the vitamin may inflame the coronary arteries, which has been linked to increased risk of heart attack.
ē Autoimmune diseases. Deficiencies can weaken the bodyís response to infection. Population data suggest that as vitamin D levels go down, the risk of rheumatoid arthritis go up. A few studies have linked deficiency of vitamin D to an increased risk of insulin resistance or type 1 diabetes. A 2006 study associated higher blood levels of vitamin D with a reduced risk of multiple sclerosis.
ē Cognitive function. A recent study of about 1,300 people, 65 years old and older, associated low blood levels of vitamin D with an increased risk of depression. Several studies, including three published in 2009, linked low vitamin D levels to reduced cognitive performance in older people.
IN SEARCH OF VITAMIN D
Vitamin D is unique in that your skin manufactures it just by being exposed to the UVB rays of the sun. Many factors however, can affect this process. If you walk in the early morning or late afternoon, for example, the sun is usually not intense enough to stimulate production of the vitamin. Other factors can slow or even shut down your skinís vitamin D factory, including sunscreen and protective clothing, or being older or overweight (fat holds onto vitamin D, making it less available to the body).
As you age, your skinís ability to convert UVB rays into vitamin D declines, so itís almost impossible to get enough vitamin D from sun exposure. In addition, dark-skinned individuals do not readily absorb UVB rays and therefore are at higher risk for vitamin D deficiency. Experts suggest that if you want to use the sun as one of your sources of vitamin D, then you must get out in the sun three times a week for 15 minutes between 10 a.m. and 2 p.m. without sunscreen. But the specter of skin cancer looms large and most health and medical organizations discourage any unprotected sun exposure.
Lack of sun exposure would be less of a problem if diet provided adequate vitamin D. But there arenít many vitamin D-rich foods (see chart) and you need a lot of them to get your needed daily allowance. Dairy products as well as some breakfast cereals, orange juices, soy-based foods, and other products are fortified with about 100 IU a serving. But most people donít eat enough of those foods to consistently cover all their requirements. People who have trouble absorbing fat such as those with Crohnís disease or celiac disease canít get enough vitamin D from the diet no matter how much they eat (vitamin D requires some dietary fat in the gut for absorption). And people with liver or kidney disease are often deficient in vitamin D, because these organs are necessary to convert the precursor to the active form of the vitamin, whether it comes from the sun or from food.
Manufacturers of multivitamin and calcium supplements have increased the amount of vitamin D in many of their products to 800 IU. If you donít already take one of these, you can buy vitamin D supplements relatively inexpensively. Consider looking for ones that contain vitamin D3, which is more potent than D2.
Growing awareness of vitamin Dís benefits, coupled with the risk of vitamin D deficiency, has led some experts to recommend a blood test that assesses the amount of vitamin D in the body. The test measures the concentration of 25-hydroxyvitamin D3 or 25(OH)D, the precursor produced by the skin and converted by the body to vitamin D. Although there is no agreement on what should be the optimal level of 25(OH)D, deficiency is generally defined as a blood level less than 20 nanograms per milliliter, or 20ng/mL (see chart). Levels that low have been linked to poor bone density, falls, fractures, cancer, immune dysfunction, cardiovascular disease, and hypertension. Many experts recommend a level of at least 32 and suggest that 800 to 1,000 IU of vitamin D per day is required to maintain that level.
HOW MUCH VITAMIN D SHOULD YOU TAKE?
The official recommended daily intake for vitamin D, devised by the US Institute of Medicine, is 200 IU for people 50 and younger, 400 IU for those 51 to 70, and 600 IU for those 71 and older. Most people donít consume that much vitamin D, unless they drink lots of milk and/or take a multivitamin. However, many researchers now believe that these guidelines are too low, and that a better goal for everyone, especially those over 60 and/or with darker skin, is 800 to 1,000 IU a day. Some people with low blood level of vitamin D may need even higher intakes to reach the desirable range.
Thus, 15 leading nutrition experts have urged the Institute of Medicine to increase its recommended intakes of vitamin D. Meanwhile, the Canadian Cancer Society now advises all Canadian adults to take 1,000 IU of vitamin D a day during fall and winter, and older and dark-skinned people to take this much year round.
When shopping for a supplement, read the fine print: Look for D3 (also called cholecalciferol), which is more potent than D2 (ergocalciferol). Do not take cod liver oil for its high levels of vitamin D, since itís also rich in vitamin A, which may weaken bones if you overdose. Eat fatty fish instead, which is rich in vitamin D but not in vitamin A.
The official ďupper limitĒ for vitamin D, set many years ago, is 2,000 IU a day. Itís possible to get that much, or more, if you consume milk, other fortified foods, and fatty fish, and also take a multivitamin and combined calcium/vitamin D supplement. However, a review article in the American Journal of Clinical Nutrition last January 2008 concluded that vitamin D is not toxic up to 10,000 IU a day. Experts donít recommend that much, but you neednít worry if you get somewhat more than 2,000 IU.
Bottom line: Itís too early to recommend vitamin D testing for everyone. The large, long-term clinical studies that would justify routine screening have not yet been done. But talk to your doctor about testing, especially if you are over 60, for instance, or have low bone density. In any case, consider taking 800 to 1,000 IU of supplemental vitamin D a day. For most people, that should raise blood levels to the desirable range (above 30 ng/mL) or at least close to it.
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Resources: ďVitamin D: Are you getting enough?Ē UC Berkeley School of Public Health Publication, February 2008; ďVitamin D offers myriad benefits,Ē Weill Cornell Medical College Womenís Health Advisor, June 2009; ďVitamin Dís effects go far beyond strong bones.Ē Mount Sinai School of Medicine Focus on Healthy Aging, December 2009
Source: PhilSTAR.com , Health and Family Section, 28 July, 2010