Vitaminen
tegen gehoorschade*
Uit een studie met cavia’s blijkt dat vitaminen kunnen helpen gehoorschade te
verminderen. De cavia’s kregen dagelijks een uur voorafgaande aan een vijf uur
durende geluidsblootstelling van 120 dD, of de vitamines A,C,E en Magnesium
alleen of een combinatie of een placebo. 120 dB is het geluid dat u hoort als u
vlak bij een straaljager staat, die gaat opstijgen. Na vijf dagen bleek dat de
combinatie van hoge dosis vitamine A,C,E met magnesium zeer duidelijk de
gehoorschade deed beperken. Vermoedelijk doen de vitamines de vrije
radicalenschade, die normaal ontstaat door het enorme geluid deels opruimen.
Nutrients
Might Prevent Hearing Loss, New Animal Study Suggests
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 formulation.
"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," says Miller.
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 protective effects.
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 conditions.
"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 Healt´. 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 loss.
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 Miller. Reference: Free Radical Biology & Medicine, 42 (2007) 1454-1463
(April 2007)