Alcohol & Hearing

28 November 2016

It's hard to pinpoint exactly. But at every party, there comes a stage when the mood picks up. People have drunk enough alcohol to reach the point where they loosen their inhibitions, and start relaxing and dancing. The observable link to the effect of the alcohol is that the noise level goes up with the mood.

Why does the party get louder when people drink more alcohol? What is alcohol doing to your brain, and what are the flow-on effects?

Alcohol, known as ethyl alcohol, or C2H5OH, has wondrous properties. It can remove oil stains from the garage floor, and store body parts or axolotls beautifully for centuries.

In humans, drinking small quantities of this versatile liquid can improve mood and self-confidence, and get the conversation flowing. But in bigger doses, the effects are less wondrous. Alcohol then interferes with your fine muscle control and your higher mental functioning, which messes with your decision making.

But getting back to party mode, why are you getting that sudden increase in noise?

We're still not entirely sure, but it seems to involve a feedback loop - let me explain. Once you have a few drinks, your sense of hearing is impaired. So when you speak, you mistakenly think that you are talking more softly than usual. To compensate, you (without even thinking about it) automatically start talking louder.

We should also factor in social competition and loss of inhibition. As people try to get their 'words of wisdom' across, there is a bit of 'shouting-down-the-competition'. This is called the Lombard Effect (after √Čtienne Lombard, a French otolaryngologist, who discovered it in 1909).

Interestingly, alcohol effects on hearing are different for men and for women. Women go deafer than men.

In typical studies, men and women (in a double blind situation) drank juice, either with, or without, alcohol. Then, once the people drinking alcohol hit around 0.03% blood alcohol concentration (BAC), their hearing was tested at six different audio frequencies running from low to high (250 Hz, 500 Hz, 1,000 Hz, 2,000 Hz, 4,000 Hz and finally 8,000 Hz). On average, the men would lose two to nine decibels (dB) of hearing, while women would lose more - five to twelve decibels. A lot of the hearing is lost around the 500-1,000 Hz range - which are the frequencies where a lot of speech happens, and where vowels are discriminated.

Unfortunately, in most of the studies, the sample sizes are rather small. From this limited data, the trend seems to be that women, fat people, unhealthy people, older people, and those with a history of heavier drinking lose more of their hearing in each drinking event. Luckily, within a week of the drinking event, the hearing tends to return to pre-alcohol drinking levels. Overall, most of the temporary hearing loss was down at the lower frequencies.

However, the hearing loss was different for long-term drinkers. They tended to have permanent hearing loss, and more often, at the higher frequencies.

We're not sure why.

We know that sound information is carried from your eardrum to the central processing centres inside your brain.

How does alcohol make you slightly deaf? Where in the hearing chain does alcohol make you slightly deaf? We have some tantalising hints from the relatively few studies done, but the simple answer is that we don't know.

This hearing loss might be from the alcohol having a direct toxic effect on the cochlea, or a subtle influence on neurotransmission, or a direct anaesthetic effect or osmotic effect on nerves or hair cells in the cochlea - or changes in impedance of the moving bones of the inner ear, or something else. We don't really know how.

The alcohol might be acting on your eardrum, or the muscles that can pull on the eardrum to quieten down the outside world, or the cochlea, or the cochlear nerve that carries the information into your brain, or it could be acting on the area in your brain that processes this information.

Regardless of the exact pathway by which it happens, the result once you've had a few drinks is that you 'hear' yourself as if you are talking too quietly, and to compensate, you start talking loudly.

There are many causes of hearing loss in our modern industrial world. Social drinking in the evening for most people usually happens in a noisy bar. This adds to the noise-induced hearing loss the party-goers get exposed to in everyday life.

We worry about getting blind drunk. But maybe another concern for the inebriated, is getting deaf drunk ...