We need to stop the
IF your ears were ringing during the recent
Fourth of July fireworks, you experienced
first-hand the dagger-like effect of intense
sound waves on your inner ear.
No surprise. Firecrackers explode with
decibels so great that a sudden dose of more
than a few minutes in duration could make
one permanently stone-cold deaf.
This is no old wives' tale, though most of
the time, noise-induced loss of hearing
creeps up painlessly and silently. All too
many middle-agers are just finding that out
as they line up for their hearing aids in
search of relief from those strained conversations in crowded rooms, where everyone
around them seems to be mumbling.
Waiting to join them in line are the growing ranks of younger people. A Harvard survey of adolescents and young adults reported
that more than half had taken a hit to their
hearing at loud music events, either tinnitus
or temporary deafness. And from my observation, most seem to have iPods attached to
For them, and the others who can still hear
a pin drop, it's smart to pay attention to the
health of the inner ear, the nerve centre for
making sense of sound.
Loud noise destroys nerve endings in the
inner ear and is a common and preventable
cause of hearing loss.
Decibels measure loudness: Silence is zero
and the explosion of a firecracker, 150 dB. A
rock concert can get up to 140; a noisy bar,
almost 100. As a general rule, a whisper is 30
dB; the purr of a quiet motor is 40, and a
normal conversation, 60. Regular exposures
to levels over 85 are toxic to the ear. The
blast of a jet engine or an Indy racing car and
an explosion or gunshot are obvious culprits.
But it's the power tools and lawn mowers,
the blare of music through earphones, the
hair dryers and vacuum cleaners and noisy
places that cause damage gradually over
time. And you don't need a decibel meter to
know what's too loud: If you have to raise
your voice to be heard above the din, you are
in a toxic place.
Deafening sounds are like blinding light,
pointedly destroying the very organ that
detects them. This irony is testimony to an
evolved life, in which the human ear has just
not kept up with modern times.
That is, the hair-like, specialised nerve
endings that are lined up inside a coiled,
fluid-filled compartment of the inner ear can
be shaken to death by loudness they were
not designed to handle.
These nerve endings vibrate at different
rates in response to different sound frequencies, more slowly for the low pitch of a baritone and faster for the higher pitch of a
soprano, transforming them into distinct
electrical impulses sent through the auditory
nerve to the brain.
Just as you can blow out an electrical circuit
by overloading it, these vibrating hair cells can
be overexcited by too much noise. When
forced into metabolic overdrive, the cells spin
off toxic oxidation products that make them
swell and sometimes slowly die off.
Toxic noise also compromises blood flow to
the inner ear, causing further damage. The
cells that go first are those that resonate to a
higher pitch, and the resulting dropout of
higher-frequency sounds is what makes words
Recognition that these nerve endings were
designed for a quieter time, when men hunt-
ed with bows and arrows and women
washed their clothes in babbling brooks, has
inspired preventive efforts that were not
even considered a few years back.
Neurobiologist Josef Miller from the
Kresge Hearing Research Institute at the University of Michigan stresses noise
avoidance and when a loud sound environment is
unavoidable, earplugs or muffs, which can
cut noise by 30 DB or more. These measures
have been incorporated into most occupational safety programmes and inspired such
innovations as quieter hair dryers and volume-limited iPods.
Just recently. Apple filed a patent for new
software designed to track a headphone
user's exposure to loud music and automatically reduce volume as needed.
On the horizon is a nutrient bar to fight off ear damage, says Miller. He
and others have shown that a combination of the antioxidant vitamins A. C,
and E and magnesium not only protects the inner ear when taken before noise
exposure but can limit damage for up to 72 hours after the insult. This
approach would add to current ear-protection devices or help those who can't
or won't wear earplugs or muffs.