Nutrients May Prevent Noise Induced Hearing Loss
Editor: We've seen promising medical advances in the field of
preventing noise induced hearing loss (NIHL). Now researchers at the
University of Michigan are reporting that daily high doses of certain
vitamins may also be effective in preventing NIHL. Here's the press
Soldiers exposed to the deafening din of battle have little defense
against hearing loss, and are often reluctant to wear protective gear
like ear plugs that could make them less able to react to danger. But
what if a nutritious daily "candy bar" could prevent much of
that potential damage to their hearing?
In a new study in animals, University of Michigan researchers report
that a combination of high doses of vitamins A, C, and E and magnesium,
taken one hour before noise exposure and continued as a once-daily
treatment for five days, was very effective at preventing permanent
noise-induced hearing loss. The animals had prolonged exposure to sounds
as loud as a jet engine at take-off at close range.
Clinical trials of a hearing-protection tablet or snack bar for
people could begin soon, and if successful such a product could be
available in as little as two years, says Josef M. Miller, Ph.D., the
senior author of the study, which is published online in the journal
Free Radical Biology and Medicine. Miller is a professor in the
Department of Otolaryngology at the U-M Medical School, and former
director of the U-M Health System's Kresge Hearing Research Institute,
where the study was performed.
Convinced by emerging evidence that nutrients can effectively block
one major factor in hearing loss after noise trauma - inner ear damage
caused by excessive free radical activity - Miller has launched a U-M
startup company OtoMedicine that is developing the vitamin-and-magnesium
"These agents have been used for many years, but not for hearing
loss. We know they're safe, so that opens the door to push ahead with
clinical trials with confidence we're not going to do any harm,"
The formulation the researchers used built on earlier animal studies
showing that single antioxidant vitamins were somewhat effective in
preventing hearing loss, and on studies of Israeli soldiers given
magnesium many days prior to exposure, who gained relatively small
In the U-M study, noise-induced hearing loss was measured in four
groups of guinea pigs treated with the antioxidant vitamins A, C and E,
magnesium alone, an ACE-magnesium combination, or a placebo. The
treatments began one hour before a five-hour exposure to 120 decibel
(dB) sound pressure level noise, and continued once daily for five days.
The group given the combined treatments of vitamins A, C and E and
magnesium showed significantly less noise-induced hearing loss than all
of the other groups.
"Vitamins A, C and E and magnesium worked in synergy to prevent
cell damage," explains Colleen G. Le Prell, Ph.D., the study's lead
author and a research investigator at the U-M Kresge Hearing Research
Institute. According to the researchers, pre-treatment presumably
reduced reactive elements called free radicals that form during and
after noise exposure and noise-induced constriction of blood flow to the
inner ear, and may have also reduced neural excitotoxicity, or the
damage to auditory neurons that can occur due to over-stimulation. The
post-noise nutrient doses apparently "scavenged" free radicals
that continue to form long-after after this noise exposure ends.
In the past 10 years, scientists have learned that noise-induced
hearing loss occurs in part because cell mitochondria in the ear churn
out damaging free radicals in response to loud sounds. "Free
radical formation bursts initially, then peaks again during the days
after exposure," explains Le Prell.
The antioxidant vitamins and magnesium used in the study are widely
used dietary supplements, not new drugs, and therefore they don't
require the extensive safety tests required for new drug entities prior
to use in clinical trials. The doses to be used in proposed human trials
will be within the ranges considered safe according to the Institute of
Medicine and federal nutrition guidelines.
"Ultimately, we envision soldiers would have a nutritional bar
with meals and it would give them adequate daily protection," says
Miller. Similar bars with other formulations are already given to
soldiers to help them withstand hot weather and other war zone
"Other people would likely benefit by consuming a pill or
nutritional bar before going to work in noisy environments, or attending
noisy events like NASCAR races or rock concerts, or even using an iPod
or other music player," says Le Prell. "Based on an earlier
study with other antioxidant agents, we think this micronutrient
combination will work even post-noise."
That study suggested a "morning after" treatment, that
might minimize hearing damage for soldiers, musicians, pilots,
construction workers and others - even if they don't take it until after
they experience dangerous noise levels. It was highlighted by the
National Institutes of Health on the NIDCD website at www.nidcd.nih.gov/research/stories/archives/06/08_01_06.asp.
If effective, such pre- and post-noise treatments could have
far-reaching effects. About 30 million Americans regularly experience
hazardous noise levels at work and at home, according to the National
Institute on Deafness and Communications Disorders. Hunting,
snowmobiling, using machines such as leaf blowers, lawnmowers and power
tools, and attending or playing in loud music concerts commonly expose
people to dangerous noise levels. Noise levels above 85 decibels damage
hearing. About 28 million Americans have some degree of hearing loss.
For about a third of them, noise accounts at least in part for their
The U-M study also adds strength to research efforts under way in
many research centers to learn how these nutrients might be used to
treat many illnesses. "Similar combinations have been very
effective in preventing macular degeneration, and many of these agents
have been used with Alzheimer 's and Parkinson's diseases, stroke-like
ischemia, and other conditions that involve neural degeneration,"
Le Prell says. "You're always hoping as a basic scientist to find a
commonality like that, across other disease processes," says
U-M has applied for patents covering the use of this unique
combination of vitamins and minerals in the prevention of hearing loss,
as demonstrated in this study; if and when revenues are generated as a
result of these commercialization efforts, the University and the
inventors of the technology stand to benefit financially. An additional
author of the study is Larry F. Hughes, Dept. of Surgery/Otolaryngology,
Southern Illinois University Medical School. The study was supported
with funds from the National Institutes of Health, General Motors
Corporation/United Automotive Workers Union, and the Ruth and Lynn
Townsend Professorship in Communication Disorders. Reference: Free
Radical Biology & Medicine, 42 (2007) 1454-1463