|Ultraviolet Light: The Good, The Bad, And The Sun |
If a little bit is good, more must be better. A bit of dark chocolate is good for the ticker, so the whole bar must be better. Try that and you’ll need another hole in your belt. A modicum of vitamin A is good for night blindness, so a few more capsules might eliminate my need for spectacles. Maybe so, but your skin’ll turn yellow as your liver rides into the sunset. With lots of things, a little bit is good. Period. That includes sunshine.
What good comes from being in the sun for a while? It increases endorphins and the consequent feelings of well-being, while countering seasonal affective disorder, a mild form of depression caused by lack of sunlight (Kegel, 2009) (Praschak-Rieder, 2008). Sun exposure may have a profound effect on blood pressure (Opländer, 2009), even at moderate doses. Everybody knows that sunlight helps the body to make vitamin D, and that vitamin—actually more of a hormone—has a raft of healthful properties, including support for the skeletal and immune systems. Vitamin D, in fact, whether from the sun or from supplements or fortified foods, may be related to more than a thousand different genes that govern virtually every tissue in the body (Mead, 2008) Perhaps the most astounding boon acquired from sunshine is the protection against prostate disease (John, 2004) (John, 2007).
But how long is a while? That depends on where you live. Fifteen or twenty minutes a day of sunlight, without sunscreen, is enough to do a body good when the angle of the sun is low, as it is much of the time in the middle latitudes, even in the summer. Between the hours of 10 AM and 3 PM, though, ten minutes is probably sufficient. The closer to the equator you are, the more time you spend on the beach, the longer it takes to cut the summer grass, or the longer the stroll in the sun, the more likely you will benefit from sunscreen after initial exposure. Let common sense prevail. There’s no one-size-fits-all answer to sun exposure.
Spring is the time of year many people anticipate. Being caught up in the excitement of casting out cabin fever and the attending gremlins, they forget about protecting themselves from too much of a good thing. Dry skin and premature ageing, damage to the eyes from radiation that turns the corner on your sunglasses and other health threats, including skin cancers, loom around the corner.
As a defense against ultraviolet radiation, the amount of melanin in the skin increases with moderate exposure to the sun (or sun lamps, tanning booths, and some industrial equipment). This is the tan most avidly sought by the worshippers. Melanin’s job is to absorb UV radiation and to dissipate the energy as heat, stopping the UV from damaging the skin. Of the three types of UV radiation, it’s the UVA—the one with the longest wavelengths (approximately 400-320nm)—that gives the quick tan. It’s less intense than UVB, but travels deeper into the skin. These are the rays we need daily. Levels remain relatively constant throughout the day, but that does not excuse UVA as possibly causative of skin disease (Haywood, 2003). Ultraviolet waves longer than 335 nm will pass through glass, so it is possible to get a left-arm tan from driving and a right-arm tan from riding shotgun (Moehrle, 2003).
UVB radiation, with a wavelength of about 329-290 nm, causes tanning, burning and wrinkling of the skin. This is the type against which sunscreens have been developed. Even short-term exposure can cause sunburn, which is more serious than just peeling skin. The arcs from a welder, the lamps from a tanning bed, and even ultraviolet germicidal irradiation can cause a burn and direct damage to DNA (Krutmann, 2012). The body tries to repair the damage almost immediately by increasing melanin output to prevent further harm, all without generating free radicals. Using a sunscreen to protect from burning does not automatically imply protection from other damaging effects of UV radiation, including melanoma (Wolf, 1994). The effects of over-exposure to UVB are not instant, although a burn can happen in less than fifteen minutes. A person continues to tan (or burn) for as long as six hours after leaving the beach. That explains why the pain appears after the shower, on the way to the boardwalk. This may go on for three days.
The third type of UV radiation is UVC, a short wave that is filtered by the ozone layer…or what’s left of it. High exposure to these rays will also cause sunburn and possibly cancer. They can be isolated and used to make germicidal lamps for water purification, mold abatement, and sterilization of dental tools.
Brief contact with the sun is all that’s needed to reap benefits. But there are factors to be considered, including geography, altitude, time of year and day, weather conditions and reflection. The sun’s rays are more direct near the equator, where they need travel only a short distance to hit the earth. Additionally, the ozone layer is thinner at zero degrees latitude. The higher the altitude, the stronger the radiation because there is less atmosphere to soak it up. Seasonal variations are obvious, as is time of day. Clouds do not block UV rays, as some might think. And that hot sand you’re walking on, or the concrete walkway you’re pressure-washing will bounce those rays right back at you, meaning you’re getting hit from the bottom as well as from the top.
All this makes you squint, right? It’s worse than that. Radiation damage to the eyes is cumulative. What happens today can return to bite you decades from now. In the cells and tissues of the eye are molecules called chromophores, bodies that are responsible for the color of a substance. They absorb light from different wavelengths at different rates. If too much UV light is absorbed, the architectural elements of the eye, notably the cornea, lens and retina may be damaged. We don’t think about it, but light can hit the eye from all directions, explaining the need for wraparound sunglasses. Glass lenses are good; plastic is better, mostly because glass allows the passage of UVA more freely. Polycarbonate, impact resistant and considered evil in food packaging, inherently blocks most UV, and that can be protective against age-related macular degeneration (Glazer-Hockstein, 2006), cataracts (Neale, 2003), and something called pterygium (Solomon, 2006), which is a mass of tissue that grows over the cornea and blocks vision.
We mentioned welding arcs. These cause a condition called photokeratitis, a painful state arising from the failure to use proper eye protection when welding. But it can also happen in tanning beds, from prolonged sun exposure sans shades, and from reflection of UV radiation from sand, snow or concrete. The sensation is described as having sand poured into the eye. Recent discoveries have learned that photokeratitis may be treated with astaxanthin eye drops, intended to reduce the apoptosis (death) of cornea cells that is prompted by acute UVB exposure by reducing oxidative stress (Lennikov, 2012). Astaxanthin is a carotenoid found in microalgae, shrimp, yeast, salmon, and trout. Differing from other carotenoids, it is not converted to vitamin A.
Contact lenses have been developed that effectively absorb UVB and protect the human lens from damage (Andley, 2011). This is good news for those who sport contacts. Regular shades can attenuate UVB transmission, but only if they are the correct shape and size for the wearer, and if they are in the right position (Rosenthal, 1988). Wearing a hat can help, but sporting a baseball cap backwards while using an extended palm to shade the eyes is as worthy of ridicule as driving the car backwards so you can see where you’ve been. A survey of seekers of the bronze, taken in the early 90’s, revealed that more than forty percent seldom or never used a sunscreen, even after becoming aware of the risks (Mawn, 1993). Don’t be a statistic. An ounce of prevention really is worth a pound of cure.
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