Solar Ultraviolet: Sun Season Tips

Forrest M. Mims III

Now that summer has arrived in the Northern Hemisphere, it's important to be aware of the consequences of excessive sun exposure.

Sunburn in children and teens is related to melanoma later in life. Melanoma is the most dangerous of skin cancers.

Many older people, especially those who have long worked outdoors, develop sunlight-induced skin cancers on their faces and arms. Excessive sunlight exposure can also cause wrinkles when it breaks down the skin's connective tissue.

According to the American Cancer Society, a million cases of non-melanoma skin cancer will be diagnosed in the U.S. in 2007. The vast majority will be diagnosed in time, and only 1-2,000 will be fatal. So while non-melanoma skin cancer is by far the most common cancer, it is also among the least fatal.

The ultraviolet (UV) rays in sunlight cause burning and skin cancer. Melanin in dark skin blocks UV and reduces the risk of non-melanoma skin cancer. But some studies show that all of us are potentially susceptible to cataracts from prolonged exposure to UV. Wraparound sunglasses provide the best eye protection.

During summer when daylight savings time is in effect, the UV peaks at about 1:30 PM near the center of time zones and is high from around 10:30 AM to 4:30 PM. It's best to avoid more than several minutes of sunlight exposure during this time. You can minimize your exposure by wearing a floppy or brimmed hat, long sleeves and sun screen.

Figure 1. The solar UV index in Seguin, Texas, on June 23, 2006 (Daylight Savings Time), was as high as on a Hawaiian beach. The UV plot shown here was measured by the US Department of Agriculture at Texas Lutheran University by means of instruments maintained by the author for Colorado State University. Graphic by Forrest M. Mims III.

UV is not all bad, for it stimulates the production of vitamin D in the skin. Vitamin D allows the body to metabolize calcium and provides vital protection from rickets in children and osteoporosis in the elderly. A growing number of medical studies show that vitamin D may also provide protection against cancer of the breast, ovaries and colon, all of which are far more dangerous than non-melanoma skin cancer.

Relatively brief exposure to sunlight provides the body with ample vitamin D, but the American Academy of Dermatology “does not recommend getting vitamin D from sun exposure or indoor tanning.” Instead, the Academy recommends “Get vitamin D safely through a healthy diet that includes vitamin supplements. Don't seek the sun.” (See this link.)

Vitamin D is included in many vitamin pills and is added to some foods, including milk and some cereals. It's also found in cod liver oil and salmon. The Food and Drug Administration recommends a daily dose of 200 International Units (IU) until age 50, 400 IU from 51-70 and 600 IU over 70.

Some scientists who study the relationship of vitamin D to cancer and other ailments believe the FDA levels are much too low. They also believe that moderate sunlight exposure is an efficient way to get your vitamin D.

So do I, but don't take my word. Public libraries and the web have a wealth of information on the beneficial and dangerous aspects of sunlight exposure. I'm not a health professional, so please check these sources or your physician if you have questions.

"World of Science" columns are selected and sometimes revised from columns published in the San Antonio Express-News or the Seguin Gazette-Enterprise. The columns are intended for a general audience. Forrest M. Mims III and his science are featured online at www.forrestmims.org and www.sunandsky.org .