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Getting enough vitamin D


Using sunscreen and avoiding the midday sun can protect against skin cancer, but too little sun may contribute to deficiency in vitamin D, a hormone critical for healthy bones and more. Many Americans have low vitamin D levels and are at risk for serious health consequences.  Check with your doctor, who may recommend testing and seasonal or year-round supplements.

What is vitamin D?

Vitamin D is a fat-soluble hormone essential for growing and maintaining strong, healthy bones and supporting a strong immune system that helps protect against cancer.

Vitamin D precursors are formed in the skin in the presence of sunlight.  The kidneys convert these substances into the active form of vitamin D, which the bloodstream carries throughout the body (Adams 2010).  Immune system cells produce vitamin D as an aspect of the body’s defenses against disease.

How does vitamin D deficiency develop?

Vitamin D is produced on this skin by ultraviolet light, particularly UVB rays. Many people rely on the sun for making enough vitamin D. However there are limitations to this approach. Many American adults spend very little time outdoors. Vitamin D production from sunlight is lower in people with darker skin pigmentation, older people and those living further from the equator.  Vitamin D production is limited in fall and winter, when UVB rays are less intense. People living in the northern half of the U.S. are unable to make any vitamin D  between November and early March (Vitamin D Council 2013).

Experts agree that too many people in the U.S don’t get enough vitamin D in their daily lives (AMA 2009, IOM 2010, CDC 2012).  About 8 percent of Americans have a serious vitamin D deficiency, and another 25 percent are considered “at risk” of a deficiency (CDC 2011). Studies have found that 70 percent of breast-fed babies were deficient in vitamin D at one month (Wagner 2010).  At that age, such a deficiency can be particularly harmful because of vitamin D’s key role in growth and development.

People with darker skin make less vitamin D from sunshine, and the federal Centers for Disease Control and Prevention has found that Mexican Americans and African Americans are two to three times more likely than Caucasians to have low vitamin D levels (CDC 2011). Increased use of sun protection and higher average body weight are also associated with low vitamin D levels (Looker 2008).

What are the consequences of low vitamin D?

In human epidemiological studies, low vitamin D levels have been associated with increased cardiovascular mortality, colon cancer mortality and breast cancer risk.  They have also been tentatively linked to skin cancer, metabolic disease, hypertension and obesity (Adams 2010, Grant 2009, Tang 2010). People with inadequate vitamin D are more susceptible to upper respiratory tract infections and other microbe-caused infections (Ginde 2009).

Vitamin D promotes intestinal calcium and phosphate absorption and calcium/phosphate release from bone. Vitamin D deficiency is associated with rickets in children and osteoporosis in adults (Papandreou 2010). Calcium strengthens bones but only in the presence of vitamin D.  Too little of either can lead to osteoporosis, fractures and other bone problems.

Can sun exposure to ensure adequate vitamin D production cause skin cancer?

Physicians and scientists agree that sun protection is essential to prevent skin cancer and to reduce its toll on human health and health care costs (Gordon 2009). Strict sun protection has been shown to exacerbate vitamin D deficiency (Norval 2009, Reichrath 2009).

Exposure to ultraviolet-B rays, whether from the sun or from artificial tanning, is the most important environmental risk factor for skin cancer (IARC 2001b). The American Academy of Dermatology’s 2009 Position Statement on vitamin D concludes that “there is no scientifically validated, safe threshold level of UV exposure from the sun that allows for maximal vitamin D synthesis without increasing skin cancer risk.”  The academy recommends increased intake of foods naturally rich in vitamin D, vitamin D-fortified foods and vitamin D supplements (AAD 2009). Fortunately, supplements are readily available in the U.S.  Americans can stay safe in the sun and still maintain healthy levels of this important vitamin.

Are vitamin D supplements the answer?

Experts recommend that you have your physician test your vitamin D levels, particularly if you are at risk of deficiency, and that you take supplements if needed. Some foods contain some vitamin D but not enough to meet the daily requirement.  Too much vitamin D can cause side effects, so take only what your doctor recommends. The body regulates the amount of vitamin D it makes in the sun but cannot protect against excess vitamin D from supplements.

In 2010, the Institute of Medicine of the National Academies updated its dietary guidelines to recommend 600 International Units of vitamin D daily for people ages 1 to 70 and 800 IU for those over 70 (IOM 2010).  This  suggests that vitamin D supplementation is necessary for many Americans.

What’s the best advice?

Consult your physician to determine if you are at risk of vitamin D deficiency.  If you are, you may need a blood test and regular or seasonal vitamin D supplementation.

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