THE IMPORTANCE 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.
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.The picture of vitamin D’s 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 don’t prove cause and effect. More trials are needed to elucidate vitamin D’s 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, here’s a rundown of the areas in which vitamin D shows disease-fighting promise.
• 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 didn’t take the vitamin D supplements.
• Muscular strength. Studies have shown that deficiency in the vitamin decreases muscular strength and performance.
• 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.
• Cardiovascular disease. Low levels of the vitamin may inflame the coronary arteries, which has been linked to increased risk of heart attack.
• Autoimmune diseases. Deficiencies can weaken the body’s 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.
• 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
Lack of sun exposure would be less of a problem if diet provided adequate vitamin D.
Sun Exposure as a Vitamin D Source
Exposing yourself to sunlight is the most important source of vitamin D because sunlight is far more likely to provide you with your vitamin D requirement than food is.13 UV rays from the sun trigger vitamin D production in your skin.13-14 Lights from your home are not strong enough to produce vitamin D. Season, geographic latitude, time of day, cloud cover, smog, and sunscreen affect UV ray exposure and vitamin D synthesis.
Sunscreens with a sun protection factor (SPF) of 8 or greater will block UV rays that produce vitamin D. An initial exposure to sunlight of 10 to15 minutes allows you 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.