Does UVB radiation protect against myopia?

Dr. Andrea Bannert has been with since 2013. The doctor of biology and medicine editor initially carried out research in microbiology and is the team's expert on the tiny things: bacteria, viruses, molecules and genes. She also works as a freelancer for Bayerischer Rundfunk and various science magazines and writes fantasy novels and children's stories.

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If you send your children outside to play, you may not have to buy glasses for the offspring later. Because sunlight effectively protects against myopia - this has been shown by several studies. UVB radiation may play an important role in this.

Myopia can be described as a widespread disease - around every third German needs glasses to see clearly from a distance. It is even more extreme in Asia: there, up to 90 percent of the population without visual aids can only see blurred in the distance.

Three hours outside

To blame is too long an eyeball. This projects the image of objects and people far away in front of instead of on the retina. The result: the image appears blurry, at least until glasses or contact lenses shift the visual axis far enough.

One can counteract myopia by staying outside a lot. Researchers at the University of Tübingen have found that three hours a day in the open air achieve the best protective effect - but only on children in whom the eyeball is still changing.

The search for the why

But why is being in the open air so crucial for the development of vision? Astrid Fletcher and her colleagues from the London School of Hygiene and Tropical Medicine investigated this question.To this end, they carried out a study with around 370 people with nearsightedness and 2,800 people with normal vision.

The test subjects were on average 72 years old. With the help of detailed questionnaires, the researchers determined how much UVB radiation the test subjects were exposed to at different stages of life. UVB radiation is part of the ultraviolet radiation contained in light; it is considered to be very rich in energy and, among other things, stimulates vitamin D production in human skin. In addition, Fletcher and her team determined the concentration of various vitamins and trace elements in the blood of the study participants.

The result: those who were exposed to more UVB radiation had a lower risk of becoming myopic. The protective effect of sunlight proved to be strongest in adolescence and early adulthood, between 14 and 29 years of age. However, the scientists did not ask the test subjects about their childhood because it is difficult to remember correctly.

Fresh air instead of a library

Incidentally, the study also dispels the prejudice that people with a higher level of education tend to spend their time in dark lecture halls and libraries rather than in the fresh air. Academics wear glasses more than twice as often, but they go out into the sun not less often than less educated people.

How UVB radiation counteracts myopia has not yet been conclusively clarified by Fletcher and her colleagues. What is certain, however, is that the sun's vitamin D does not play a role here - at least that is what the blood measurements showed.

Dopamine against length growth?

Fletcher suspects that there is another mechanism behind this: light promotes the release of the neurotransmitter dopamine. From this, the experts suspect that it inhibits the elongation of the eyeball.

Spinach?

The researchers found another connection that surprised them: subjects who had a lot of lutein in their blood wore glasses less often, so they had a lower risk of being nearsighted. Lutein is a plant pigment that belongs to the group of carotenoids. It's found in kale or spinach, for example.

And the macula - the zone of sharpest vision on the retina - contains lutein. A connection with myopia was not previously known. Maybe the antioxidant properties of the molecule are behind the protective effect, says Fletcher. In any case, further research is necessary in order to further track down the possible protective factors against short-sightedness.

Source: Williams K. M. et al .: Association between myopia, ultraviolet B radiation exposure, serum vitamin D concentrations, and genetic polymorphisms in vitamin D metabolic pathways in a multicountry european study, JAMA Ophthalmology, December 2016.

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