Exercise helps keep weight off and is good for your heart, that much is well known. Now, scientists say it also seems to prevent age-related hearing loss in mice.
University of Florida researchers found that sedentary mice lost hair cells and strial capillaries, structures that are important in the auditory system, at a much higher rate than mice that exercised. This resulted in a roughly 20 percent hearing loss in sedentary mice compared with a 5 percent hearing loss in active mice.
Age related hearing loss affects about 70 percent of adults age 70 and older, and occurs when people lose hair cells, strial capillaries, and spiral ganglion in the cochlear system of their ear.
Inner Ear And Age Related Hearing Loss
Hair cells sense sound, strial capillaries feed the auditory system with oxygen, and spiral ganglion are a group of nerve cells that send sound from the cochlea to the brain. Shaped like a snail shell, the auditory system is always running, says lead author Shinichi Someya, associate professor in the aging and geriatric research department at the University of Florida College of Medicine.
“The cochlear, or inner ear, is a high-energy demanding organ. The auditory system is always on and always processing sound. To process sound, it needs a huge amount of energy molecules.”
The system needs to be well-fed with oxygen, delivered to the inner ear by strial capillaries, to generate those energy molecules.
To test how exercise affects the loss of strial capillaries, hair cells, and neurons, researchers separated mice into two groups: mice that had access to a running wheel and mice that did not have that access.
The mice were also housed individually so that the researchers could keep track of how far the mice ran on their running wheels.
The exercise regimen for the mice peaked when the animals were 6 months old, or about 25 in human years. As the mice aged—to 24 months, or 60 human years—their exercise levels decreased.
At their peak, the mice were running about 7.6 miles per day, but at the lowest, the mice were still running about 2.5 miles per day. The group of exercising mice was then compared with a control group of non-exercising mice.
The findings suggest age-related inflammation damages the capillaries and cells, and that exercising provides protection against that kind of inflammation.
In another part of the study, inflammation in the bodies of the sedentary mice was compared to inflammation in the exercising group. The mouse runners were able to keep most markers of inflammation to about half that of the sedentary group, which may help preserve the capillaries and hair cells involved in hearing.
While epidemiological studies have shown a link between hearing sensitivity and exercise, this is the first research to show that regular exercise can prevent age related hearing loss in mice, adding that the research translates well to humans, Someya says.
“Exercise likely releases some growth factors yet to be discovered that maintain capillary density as compared to the control animals who were not exercising. Also, exercise may release other beneficial factors, but can also attenuate and blunt negative factors, such as inflammation,”
says coauthor Christiaan Leeuwenburgh, professor and vice chair of research for the Institute on Aging.
Chul Han, Dalian Ding, Maria-Cecilia Lopez, Senthilvelan Manohar, Yanping Zhang, Mi-Jung Kim, Hyo-Jin Park, Karessa White, Yong Hwan Kim, Paul Linser, Masaru Tanokura, Christiaan Leeuwenburgh, Henry V. Baker, Richard J. Salvi, Shinichi Someya Effects of Long-Term Exercise on Age-Related Hearing Loss in Mice Journal of Neuroscience 2 November 2016, 36 (44) 11308-11319; DOI: 10.1523/JNEUROSCI.2493-16.2016
Image: JD Mason