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For the last 18 years, Paul Williams of Lawrence Berkeley Laboratory has been following 55,000 runners as part of the the National Runners’ Health Study, which has incredible statistical power thanks to its size and duration. These days, Williams churns out new studies like clockwork, showing the association of running with various health risks and body parts. Most recently, it’s the eyes: in three separate studies (one in Medicine & Science in Sports & Exercise, two in Investigative Ophthalmology and Visual Science), Williams shows that running reduces the risk of glaucoma, cataracts and macular degeneration. The mechanism isn’t entirely clear (epidemiological studies like this shows correlations, not causes), but Williams speculates that aerobic exercise may reduce “intraocular pressure,” the fluid pressure behind the eye.
What Williams really emphasizes in his recent studies is the “dose-response” relationship between running and health: the farther and faster you run, the greater the benefits. In this case, for instance, every additional kilometre in your average daily run lowers your glaucoma risk by five percent. Also, the faster your best 10K time, the lower your risk — in fact, there were no reported cases of glaucoma for runners who could run 10K faster than 33:20! This is quite different from the usual government health recommendations that advocate a fairly minimal amount of moderate exercise each week, and make it sound like there’s no particular benefit in doing more.