New research in mice suggests that routine exercise may protect adults from the vision loss that comes with age, but researchers say testing the theory on humans may take years, Gretchen Reynolds writes in the New York Times' "Well" blog.
What not exercising does to your brain
About the research
For a study recently published in The Journal of Neuroscience, researchers from Emory University and the Atlanta Veterans Administration Medical Center studied healthy, adult mice. Half were allowed to remain sedentary throughout the day, while the others were made to run on little treadmills for about an hour a day.
After two weeks of the exercise routine, 50% of the mice in each group were also exposed to a "searingly bright light" for four hours a day, while the others stayed in dimly lit cages. Researchers note that light exposure is a widely used method for inducing retinal degeneration in animals, although it does not exactly mimic the progression of macular degeneration—the vision loss that humans experience with age.
After another two weeks of the light routine, researchers found that the sedentary mice exposed to the light were experiencing severe retinal degeneration—nearly 75% of their retinal neurons had died. But the mice that exercised and were exposed to the light retained about twice as many retinal neurons as their sedentary counterparts.
Additionally, researchers measured their levels of brain-derived neurotrophic factor (BDNF), a substance in the brain and bloodstream that is known to contribute to the health of neurons and thus improve cognition. The mice who exercised had far more BDNF than the sedentary mice.
Need more reasons to work out?
Study authors: Exercise now, don't wait for our results
Although the study findings are promising, it is "impossible to know, based on the data we have now" that exercise will be as effective in human eyes, says co-author Machelle Pardue, adding "as potential treatments go, it's cheap, easy, and safe." Pardue says she is working on applying the theory to humans, but getting results may take years because macular degeneration is a slower process in humans.
Macular degeneration robs millions of older Americans of their vision every year. She notes that a 2009 study found long-distance runners had a lower risk of developing macular degeneration than moderate runners.
Overall, the research strongly suggests "exercise protects vision, at least in mice, by increasing BDNF in the retina," says co-author of the study Jeffrey Boatright. He adds that exercise "costs almost nothing and results in you making your own growth factors, which is so much safer and more pleasant than having a needle stuck into your eyeball" (Reynolds, "Well," New York Times, 3/26).
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