Hat tip to Abel Pharmboy for this fascinating story! A recent US government study has found that:
a) Black adults hear better than white adults
b) Women hear better than men
c) Average hearing thresholds are the same in the US as they were 35 years ago (despite the much-maligned iPod and Walkman!)
(More under the fold....)
The large-sample-size study (5,000 people) was conducted by the National Institute for Occupational Safety and Health, and mirrors the results of smaller, previous studies. This study examined hearing tests collected from 1999 to 2004 as part of a comprehensive federal health survey (unpublished, which makes me uneasy, but it IS the government....). The hearing test involved wearing headphones and pressing a button if you heard a tone (which varies in frequency and loudness).
The hearing difference between whites and blacks may be attributed to the skin pigment melanin, which some scientists hypothesize to play a role in protecting the ear from progressive hearing loss. A researcher in the study proposed that melanin may aid the removal of harmful chemical compounds caused by damage to the cochlea's hair cells. My personal opinion can add another dimension to this theory. A strip of fleshy vasculature (blood vessels) spirals around the inside of the cochlea, called the stria vascularis. This provides nutrients and oxygen to the organ of Corti (where the hair cells are), but also serves as a conduit for chemicals and drugs in the bloodstream to damage the inner ear. The guinea pigs I work with in my research are always pigmented (rather than albino, which is the norm), because pigmented guinea pigs have melanin in their stria vascular while albino guinea pigs lack it. Incidentally, this translates into pigmented guinea pigs being more resistant to hair cell damage and deafness, and makes them a better clinical model. This would also help explain why albino people have a greater incidence of hearing loss than the general population. I believe that the melanin prevents harmful chemicals from getting into the inner ear in the first place, in addition to aiding in removing them. (This would be a great grant for someone!)
As for the gender differences, the study was unable to pinpoint whether genetics or environment played a bigger role.
"Boys have typically done noisier activities," Elliot Berger [an Indianapolis-based hearing protection expert] said.
In my opinion, just as men are much less likely than women to seek out medical attention, take their medicine as they should, wear sunscreen, etc, they would also be less likely to take preventative measures to protect their hearing. I think that young girls and boys are exposed to equally "noisy" activities, but the choices of jobs later in life do tilt men to more commonly noisy jobs (construction worker, airline baggage handler or runway attendant, musician or stage hand, lawn mower, truck driver, etc).
On average, women were more sensitive to higher frequency tones (which is the first to go with age) and could hear higher tones at 11-22 decibels as compared to 19-32 decibels for men. Blacks (on average) could hear high frequency tones at 15-22 decibels, whites could hear them at 21-32 decibels, and Mexican Americans could hear them from 16-25 decibels. The lower the decibel threshold mentioned, the better the hearing of the group.
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Comments
ah, you ice people are deaf to the beauty of the world!
Posted by: razib | June 17, 2006 1:24 AM
Ah yes, but we women still got you beat. ;)
Posted by: Shelley | June 17, 2006 1:34 AM
Shelley, where did you receive your undergraduate education?
Posted by: Jeebus | June 17, 2006 2:07 AM
jeebus, what age were you when you lost your virginity? (since we're on random off topic ?'s on this thread :)
Posted by: razib | June 17, 2006 2:49 AM
If it is the melanin, then you would expect a gradient in this effect, parallel with skin color. The finding that latino/latina persons were intermediate, between black and white folks, would seem to support that. I would wonder, though, if there would be a confounding factor, with those of higher socioeconomic status being more likely to work in noisy professions.
One potential problem with this kind of research is that skin color does not always correlate well with a person's identified race. If you wanted to study this, you'd have to actually measure the darkness of the skin, and you'd have to take the measurement on a part of the skin that is rarely exposed to the sun.
Posted by: Joseph | June 17, 2006 9:40 AM
Jeebus, I went to New College of Florida, got a Biochemistry bachelors there. (http://www.ncf.edu)
Joseph, those are all excellent points. It would certiainly point to a gradient effect--especially when you consider people who are are albino can experience highened hearing loss. It would be interesting to test very dark people, and see if this holds up. And socieoeconomic factors also I'm sure have a role to play (although most the rich kids I knew got front row tickets to the concerts, so I can have the last laugh on that one). I think that, as this theory is in its infancy, measures will become more sophisticated as the results develop. There is perhaps also a little hesitance to use skin color as a rallling point on the data, cause "its been burned before." Heh.
Posted by: Shelley | June 17, 2006 10:42 AM
Wouldn't you rather expect socioeconomic status to be inversely proportional to hearing loss? Many of the noisiest jobs around (mining, heavy industry, construction, bar and nighclub work) are low on the socioeconomic ladder, while many of the quieter ones (librarian, author and columnist, software development) are fairly high. Also, I'll go out on a limb and say that in general the awareness of (and concern about) hearing damage is higher among those with higher education.
Posted by: Janne | June 17, 2006 11:03 AM