Regular, vigorous physical exercise may lower the risk of visual loss and help preserve eyesight, two new studies in a large group of runners show.

The more miles the men and women ran, the less likely they were to develop age-related macular degeneration (AMD), a deterioration of the central portion of the retina that is a major cause of vision loss and blindness among older people. Running also lowered the cataract risk for men.

“We often think of loss of vision as we get older as sort of an inevitable consequence of aging,” Dr. Paul T. Williams of the Ernest Orlando Lawrence Berkeley National Laboratory, California, who conducted both studies, told Reuters Health. “I think what we are seeing is that there are things people can do when they’re younger to prevent that.”

More than half of men and women older than 65 years have cataracts, a clouding of the lens covering; while 28 percent of Americans 75 and older have AMD, Williams notes in the studies, which are published in the journal Investigative Ophthalmology & Visual Science. Aging, sun exposure, diabetes, obesity and other factors may contribute to the development of cataracts, he adds, although poor fitness and sedentary lifestyle don’t seem to be cataract risk factors. While exercise is also not seen as a way to prevent AMD, which has been linked to cigarette smoking and obesity, three studies suggest that it could.

The researcher investigated the relationship between exercise and vision loss in the National Runner’s Health Study, which includes nearly 42,000 men and women 18 or older recruited between 1991 and 1993. During 7 years of follow-up, 733 of the men and 179 of the women developed cataracts, while 110 men and 42 women reported being diagnosed with AMD.

The longest-running, leanest, and speediest men were all at lower cataract risk, Williams found, although there weren’t enough women who developed cataracts to conduct a more detailed analysis.

The body mass index (BMI) of the patients was measured - the ratio of height to weight that is often used to determine if an individual is obese or overweight. A normal BMI is between 18.5 and 24.9; lower than 18.4 is underweight and 30 or higher is considered obese.

Men with a BMI higher than 27.5 had an 88-percent greater likelihood of developing cataracts than men with a BMI lower than 20.

The risk for men who ran at least 64 kilometers a week - or nearly 40 miles was 35-percent lower than for the men who ran less than 16 kilometers, or about 10 miles, weekly. Men who ran faster than 4.75 meters per second had half the cataract risk of the slowest runners.

And for both men and women, Williams found, AMD risk declined as mileage rose. On average, people diagnosed with the vision condition ran less than those who hadn’t been diagnosed. Risk for runners who logged 2 to 4 kilometers a day (1.2 to 2.5 miles) was 19 percent lower than for those who ran less, while people who ran 4 or more kilometers daily cut their risk by 42 percent to 54 percent.

The least active runners in the study, who averaged less than 2 kilometers a day, were getting about the minimum amount of exercise recommended by current guidelines, which suggests people walk briskly for 30 minutes a day 5 days a week, Williams noted. Although there are clearly health benefits to meeting these minimal standards compared to being sedentary, he added, the findings provide yet more evidence that more exercise is good for one’s health.

SOURCE: Investigative Ophthalmology & Visual Science, January 2009.