Palo Alto, CA —News outlets, fitness magazines, and health bloggers churn out hundreds of articles on the health benefits of exercise. And most people can tell you that exercise is an important factor in warding off heart disease, diabetes, cancer, and depression. What isn’t widely known is the role exercise plays in keeping aging or diseased eyes healthy.
Vinit Mahajan M.D., Ph.D., Stanford professor and vice chair of ophthalmology research, said, “It makes sense that exercise is linked to eye health. Exercise increases blood flow and nutrients to the whole body, including to the retina and optic nerve. Exercise fundamentally changes the basic molecular metabolism of cells.”
Retinal degeneration, diabetic retinopathy, and glaucoma are linked to other health problems, including high blood pressure, diabetes, and high cholesterol levels. Recent studies suggest exercise may help keep these diseases at bay or at least limit their negative impact on overall health.
Mahajan also sees the recent evidence coming out of research labs linking improved memory, cognitive function, and overall brain health to exercise as further reason to believe exercise should be part of an eye patient’s prevention and treatment plan.
He said, “The retina is an extension of the brain, and what benefits the brain is likely good for the eyes.”
Studies using mouse models of retinal disease are revealing the role exercise may play in protecting against blinding eye diseases.
Exercise decreased the growth of harmful blood vessels in the eyes of mice compared to those that did not exercise. This is a significant finding since an overgrowth of choroidal blood vessels near the retina is linked to macular degeneration, a leading blinding eye condition that affects as many as 11 million people in the United States, and this number is expected to double to nearly 22 million by 2050.
Another mouse model of retinal degeneration caused by excessive light exposure showed less damage when mice underwent exercise.
Mahajan said, “This research is exciting because it demonstrates that patients have some control over their eye health. Physicians and patients have another tool in their toolkit to fight retinal disease. It also emphasizes the need to keep our elderly patients mobile.”
Researchers at Emory University created a mouse model with retinal degeneration and compared degenerative outcomes between mice that electively ran on a wheel with mice that had their wheels locked. The mouse disease was similar to a human genetic retinal disease where mutations in the rhodopsin gene cause progressive, irreversible vision loss. Mice that ran on a wheel were found to be partially protected against retinal degeneration and inflammation.
Other studies have found that people who exercised seven hours a week were less likely to develop age related macular degeneration compared to their sedentary counterparts. Exercise that increases blood flow like brisk walking, cycling, and swimming is recommended.
In the case of glaucoma, which is a degeneration of the optic nerve, research has shown that people who engaged in moderate physical exercise like walking, mowing the lawn, and dancing were less likely to develop glaucoma than people who were inactive. Moderate exercise has been shown to lower intraocular pressure, which is a hallmark of glaucoma.
A National Health and Nutrition Examination Survey found that participants who spent the day standing or walking versus sitting had 58% decreased odds of glaucoma, and participants who performed moderate amounts of vigorous activity had 95% decreased odds of glaucoma compared with those who performed no vigorous activity.
Mahajan said, “Long term exercise changes the body at the molecular level. Current clinical imaging only allows us to see macroscopic physical changes inside the eyes. With newer molecular technologies like proteomics, metabolomics, gene expression analysis, and adaptive optics, it won’t be long until we know the exact molecules active in eye cells during exercise.”
Researchers do have some insight into what’s happening in other cells after exercise. In a study from Stanford University, researchers measured thousands of molecules in blood samples collected from 36 individuals who reached maximum oxygen consumption on a treadmill. At two minutes after exercise, the participants experienced a boost in molecular markers of inflammation, tissue healing, and oxidative stress. During the same period, blood samples revealed the body was metabolizing amino acids for energy, and at fifteen minutes switched to metabolizing glucose, a type of sugar. In resting blood samples, similar molecular signatures were found in the most physically fit participants. The team predicts that in the future a simple blood test may be able to measure a person’s physical fitness.
“These molecular changes in the blood would certainly impact retinal and optic nerve health,” Mahajan said.
Some of the exercise-related molecules that could impact retinal health were identified in Mahajan’s lab.
“While studying mice with a genetic form of retinal degeneration, we found that a key set of energy enzymes called the “TCA Cycle” were depleted. By feeding mice the metabolite alpha-ketoglutarate, we were able to significantly delay retinal degeneration. The same set of energy enzymes are affected by exercise,” Mahajan said.
Many of the cellular energy enzymes are connected to mitochondria, the small organelles that operate as chemical energy factories producing the power cell's need to create biochemical reactions.
“The retina contains thousands of mitochondria that provide the energy retinal cells need to turn light into electrical signals,” Mahajan explained. “When mitochondria are defective, retinal cells die. They may also underly retinal aging. At Stanford we are investigating ways to enhance mitochondrial metabolism specifically for eye disease.”
Mahajan said, “Education is the key to preventative medicine, so I make a point of talking about the benefits of exercise with my patients, even those with rare retinal genetic conditions. I emphasize that exercise needs to be part of a patient’s routine to have a positive impact on their eyes – and on the rest of their physical and mental health. Patients don’t always have to go to a gym or hire a personal trainer. Incorporating a morning and evening walk into their days also counts.”
He added, “In the lab, we are working to find the specific molecules and signals triggered by exercise, and one day, we may be able to enhance this natural protective mechanism.”