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Mims: It's a balancing act for UV ray exposure
By Forrest Mims : June 29, 2012 : Updated: July 1, 2012 9:24am
Photo By Forrest M. Mims III/For the Express-News
Exposure to UV can be higher when the sun is near a cloud and the sky is clear and blue, as illustrated by this pinhole photograph.
Ultraviolet sunshine stimulates the production of vitamin D in human skin. But excessive UV can cause skin cancer.
Now that the sun has reached its highest point in the sky, it's time to consider how best to balance these contradictory consequences of UV.
We can learn about common-sense sun safety from the Australians, who receive much higher levels of solar ultraviolet during their summer than we do.
That's because Earth's orbit around the sun is slightly elliptical.
During the Southern Hemisphere summer, Earth is closer to the sun than during the Northern Hemisphere summer.
Ozone key in sun safety
The ozone layer absorbs UV, so it also plays a key role in sun safety.
Because of diminished ozone over Antarctica during the Southern Hemisphere spring, Australia sometimes receives higher than usual UV during October.
These factors and an outdoor lifestyle give Australia the world's highest skin cancer rate.
In 1981, a public relations campaign was begun to encourage people to reduce their exposure to UV sunshine.
The campaign theme was "Slip on a shirt, slop on some sunscreen and slap on a hat."
They found that it was "hugely successful" in reducing skin cancers except melanoma, which is increasing.
They also found that "We now face an epidemic of vitamin D deficiency in Australia."
Vitamin D deficiency
Vitamin D deficiency is related to a growing number of health issues, including cancers that are far more serious than nonmelanoma skin cancer.
Many scientific papers have reported new discoveries about the importance of vitamin D.
The unexpected consequence of vitamin D deficiency from Australia's campaign suggests that common-sense sun exposure is better than an outright ban. The Vitamin D Council (www.vitamindcouncil.org) and other sources suggest that 10 to 15 minutes of exposure to direct sunshine several days a week during summer and more often more during winter will keep vitamin D at a healthy level.
People with dark skin need more UV.
On hazy days, you can receive a sunburn in the shade.
Cumulus clouds near the sun when the sky is clear and blue can increase UV.
If you have easily burned skin, it might be good to talk to your physician about nonprescription vitamin D supplements. Since our eyes are vulnerable to UV, it's important to wear UV-absorbing glasses or sunglasses when outdoors, especially within a few hours of solar noon (1:36 CDT today). Shielding the eyes of infants from direct sunlight is equally important.
Forrest Mims III, an amateur scientist whose research has appeared in leading scientific journals, was named one of the 50 Best Brains in Science by Discover Magazine. His science is featured at www.forrestmims.org. Email him at firstname.lastname@example.org.