Are We Getting Enough Sun?

As the onset of winter begins to shorten our days and drive us indoors, our exposure to the sun is diminished. This can be a boon to those who can't stand the heat, or those who have fair skin. But could we be missing out on a very important aspect of being out in the sunshine? While most people know the risks of too much exposure to the sun's harmful rays, such as a higher risk of skin cancer, few of us stop to consider the risks of too little sun.

Simply put, exposure to the sun helps our bodies make vitamin D. Ultraviolet rays from sunlight trigger vitamin D synthesis in the skin, creating vitamin D for our bodies to use. A deficiency in this important vitamin can cause serious health problems, and vitamin D deficiencies are becoming more common than most of us realize.

Jacquelyn Dinusson, MD, Assistant Clinical Professor of Family and Community Medicine at the Medical College of Wisconsin, says that vitamin D deficiency occurs worldwide from dietary insufficiency, malabsorption of the vitamin by the intestines, and lack of exposure to the sun. It causes the bone disorder known as rickets, or osteomalacia, which is a weakening or softening of the bones, and it can lead to other health problems as well.

Dr. Dinusson explains, "Vitamin D assists with the absorption of calcium, with bone calcification, and with the reabsorption of calcium in the kidneys. Symptoms of vitamin D deficiency can include persistent nonspecific bone pain and muscle weakness. It may also cause symptoms associated with low calcium, including numbness around the mouth or in the extremities, abnormal heart rhythms, or spasms of the hands or feet." In addition, she says, vitamin D deficiency can lead to osteoporosis, or bone fractures from minimal trauma.

Who's at Risk?
Dr. Dinusson reports that the people most at risk of vitamin D deficiency are those with inadequate dietary intake of vitamin D and those with minimal sun exposure. This includes people who are malnourished, homebound, darker-skinned, or those living in a northern latitude. Additionally, exclusively breastfed infants without adequate vitamin D supplementation are at risk. "Infants drinking milk substitutes (unfortified soy, rice, almond, and oatmeal drinks) prior to one year of age may have vitamin D deficiency," Dr Dinusson says. Lastly, those who experience difficulty absorbing vitamin D are at risk. This can include people with liver or kidney disease and people taking certain drugs, including some seizure medications.

How Much Is Enough?
Physicians have a variety of methods for diagnosing a vitamin D deficiency if patients show symptoms. Otherwise, Dr. Dinusson gives us some general guidelines to follow: "The recommended daily intake of vitamin D for infants and children is 200 IU of vitamin D per day. Healthy adults require 400 IU daily, and those with certain medical problems or who are over seventy years old require 600 to 800 IU per day." There are a few foods that contain vitamin D, including egg yolks; fatty fish like sardines, mackerel, salmon, and herring; fish liver oils; shrimp; chicken liver; and oysters. Additionally, some foods are fortified with vitamin D, including cow's milk, breakfast cereals, and infant formulas, says Dr. Dinusson.

Eating foods that contain vitamin D is good, but exposure to the sun is much more efficient. According to the US Centers for Disease Control and Prevention (CDC), sun exposure is perhaps the most important source of vitamin D, because normal exposure to sunlight provides most humans with their total vitamin D requirement. However, season, geographic latitude, time of day, cloud cover, smog, and sunscreen use all affect UV ray exposure and vitamin D synthesis.

For example, sunlight exposure from November through February in Boston is insufficient to produce significant vitamin D synthesis in the skin. Complete cloud cover halves the energy of UV rays, and shade reduces it by 60%. Industrial pollution, which increases shade, also decreases sun exposure. Sunscreens with a sun protection factor (SPF) of 8 or greater will block UV rays that produce vitamin D, but it is still important to routinely use sunscreen to help prevent skin cancer and other negative consequences of excessive sun exposure.

An initial exposure to sunlight (10 -15 minutes) allows 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.

Supplements
Supplements can play an important role for those who aren't getting enough vitamin D. Dr. Dinusson says the American Academy of Pediatrics recommends a minimum intake of 200 IU per day of vitamin D to exclusively breastfed children, starting within the first two months of life, unless the infant is also drinking more than 500 ml daily of vitamin D-fortified formula. At least 200 IU of vitamin D daily is also recommended for children and adolescents who do not have regular sunlight exposure or ingest greater than 500 ml daily of vitamin D-fortified milk.

"For elderly people," Dr. Dinusson says, "800 IU of vitamin D per day, along with calcium supplementation, may reduce hip fractures in residents of nursing homes or the frail elderly. I also recommend at least 400 IU of vitamin D with calcium supplementation to those diagnosed with osteoporosis. Anyone with risk factors for vitamin D deficiency, including lack of sun exposure, malabsorption of vitamin D, or dietary insufficiency should consider vitamin D supplementation."

Overall, Dr. Dinusson advises getting some exposure to sunshine every week, and eating foods that contain vitamin D. If you think you might be at risk for vitamin D deficiency, or exhibit any of the symptoms noted above, be sure to call your health care provider for testing.

P.J. Early
HealthLink Contributing Writer

This article includes information from the US Centers for Disease Control and Prevention.

MCW Health News presents up-to-date information on patient care and medical research by the physicians of the Medical College of Wisconsin.