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Summertime brings barbeques, swimming, family outings, hiking, and lots of fun in the sun. We all know that sunlight is essential for health, but along with its obvious benefits, it also carries the risks of skin cancer and aging.

Some exposure to sunlight is healthy. Most experts agree that approximately 20 minutes of daily exposure to natural light is beneficial for health. This exposure to sunlight does, however, carry some risks.

The sun emits long-wave ultraviolet A (UVA) and short-wave ultraviolet B (UVB) light rays:

  • UVA rays account for up to 95 percent of the UV radiation reaching the earth’s surface from the sun and are the “tanning” rays.
  • While less intense, UVB rays are 30 to 50 times more prevalent than UVA rays, are present all year long during daylight hours, and can penetrate glass and clouds.

While both types penetrate the atmosphere and play an important role in premature skin aging, eye damage (including cataracts), skin cancers, and immunosuppression, UVB light from natural light exposure can kick-start the metabolic chain reaction that produces vitamin D. Benefits of this important vitamin include better bone health; improved immune function; reduced risk of illnesses ranging from multiple sclerosis and osteoporosis to breast cancer, prostate cancer, and diabetes; and a lower incidence of wintertime blues (often called “seasonal affective disorder” or SAD).

Vitamin D Requirements

Current guidelines for blood levels of vitamin D are about 30 nanograms per milliliter, which means approximately 10-15% of Caucasians in the United States and 50% of the black population are deficient in summer. The numbers of those who are deficient are higher in the winter when there is less sunlight.

Until recently, vitamin D was mainly viewed as a protective agent against osteoporosis, so dietary recommendations called for a relatively small intake per day—a minimum of 400 international units (IUs). Recommendations were often twice that for individuals who did not get outdoors as much (such as the elderly or those in northern climates). The current recommended daily intake for vitamin D in adults over 20 years of age is 600 IUs per day.

Those who are exposed to the sun’s UVBs can obtain 20,000 IUs of vitamin D in 20 minutes at noon in the summer, depending on where they live. More exposure than that can damage the skin. Darker-skinned individuals may need three to five times that exposure time to produce the same result.

Sources of vitamin D (other than supplements) include cod liver oil, fatty fish (such as salmon, tuna, and mackerel), beef liver, egg yolks, some mushrooms, fortified orange juice, fortified cow’s milk, yogurt, and cheese.

Sunscreens and Vitamin D

A sunscreen’s effectiveness in blocking UVA and UVB rays is measured by its sun protective factor (SPF). SPF indicates how long it takes UVB rays to redden the skin when sunscreen is used compared to how long it takes to redden the skin without the product. An SPF of 15 means it takes the skin 15 times longer to redden than without sunscreen. An SPF of 15 or higher usually protects against UVA and UVB rays.

Sunscreens interfere with the production of vitamin D because they screen out or reflect ultraviolet light. There are two main types of sunscreens:

  • Barrier sunscreens create a reflective surface on the skin to reflect UV light. Their active ingredient is zinc oxide and/or titanium dioxide.
  • Chemical sunscreens form a thin film on the surface of the skin and contain ingredients that absorb UV light before it causes skin damage.

At this time, the Food and Drug Administration (FDA) has approved 15 active ingredients for use in sunscreens. The chemicals in them have been proven effective but have not been tested for safety.

Sunlight and Photoaging

While sun exposure can provide us with vitamin D, too much sun exposure leads to photoaging. Photoaging occurs with a combination of excess sun exposure and aging and is caused by exposure to the sun’s rays.

  • Genes and skin type play a significant role in the relationship between aging, skin cancer, and sun exposure.
  • Getting a sudden, large exposure of sunlight may be more dangerous than a steady exposure over time.
  • Exposure when you are young matters most. Childhood and adolescence are the most dangerous times to get sunburned. Getting one or more blistering sunburns in childhood or adolescence more than doubles a person’s chances of developing melanoma (the most dangerous form of skin cancer) in later life.


Because of our worries about skin cancer and aging, we have gone from sun worship to sun dread. Summer’s here. Get outside, enjoy the sun, and stay healthy by following these guidelines:

  • Avoid sunburns, blistering, and tanning booths (which increase exposure to ultraviolet rays and increase risk of cancer).
  • Protect children. They are especially vulnerable to UV rays. Babies under 12 months should always remain in the shade.
  • Limit time in the midday sun. The sun’s rays are strongest between 10 am and 2 pm.
  • Use shade wisely and follow the shadow rule: “Short shadow – seek shade!”
  • Wear protective clothing: a wide-brimmed, tightly woven hat, loose-fitting clothes, and sunglasses.
  • Use a barrier (vs. chemical) sunscreen with an SPF of at least 15. Reapply sunscreens as needed and after working, swimming, or exercising outdoors. Don’t prolong your stay in the sun even if you wear sunscreen.
  • Know the UV index—a measure of UV radiation. This can be found on your local weather report and online. The higher the index, the higher the risk of skin and eye damage. When the UV index is 3 or above, take sun precautions.