Getting enough vitamin D

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.

The body forms vitamin D precursors on the skin 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 to help the the body defend itself against disease.

How does vitamin D deficiency develop?

Many people rely on the sun for making enough vitamin D. However, many American adults spend very little time outdoors. People with darker skin, older people and those living further from the equator produce less vitamin D from sunlight.

People produce less vitamin D production in fall and winter, when UVB rays are less intense. People living in the northern half of the U.S. cannot make significant vitamin D from sunlight between November and early March (Vitamin D Council 2013).

Experts agree that too many Americans don’t get enough vitamin D in their daily lives (AMA 2009, IOM 2010, CDC 2012). About 8 percent of the population has a serious vitamin D deficiency, and another 25 percent is 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 of age (Wagner 2010). This is a serious problem because vitamin D plays a key role in growth and development. 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). People who use more sun protection or weigh more than average are more likely to suffer from vitamin D deficiency (Looker 2008).

What are the consequences of low vitamin D?

Human epidemiological studies have linked low vitamin D levels with increased mortality from heart disease and colon cancer and heightened risk for breast cancer. An international team of scientists led by researchers from Cambridge University and Rotterdam University analyzed 95 research studies and calculated that 13 percent of deaths in the U.S. could be attributed to low levels of vitamin D3 (a specific type of vitamin D) (Chowdhury 2014). Low vitamin D has been tentatively linked to skin cancer, metabolic disease, hypertension, obesity, upper respiratory tract infections and other microbe-caused infections (Adams 2010, Tang 2010, Ginde 2009).

Calcium strengthens bones but only in the presence of vitamin D. Vitamin D deficiency is associated with rickets in children and osteoporosis in adults (Papandreou 2010).

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

Physicians and scientists agree that people should use sun protection to prevent skin cancer and to reduce its toll on human health and health care costs (Gordon 2009). Strict sun protection can 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 concluded 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 that people eat more foods naturally rich in vitamin D, vitamin D-fortified foods and vitamin D supplements (AAD 2009). Since 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 one to 70 and 800 IU for those over 70 (IOM 2010). 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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