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Introduction

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A few days ago the Lancet (journal) released its Commission on "Dementia prevention, intervention, and care".

You can download/read the report here for free, although you will need to register and make an account on the Lancet website to do so.

This is basically a huge report which is collated by some of the most esteemed researchers and experts in the field, who then sift through the body of research and try to come up with guidelines and advice.

The report is, as one would expect, very long and contains a lot of information. I am still going through it but one thing I did find of interest was the information linking hearing loss and dementia.

This is a relatively new finding in the dementia field and I think it is something that most people are probably not aware of.

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The Findings

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The authors of the report were unable to find any systematic reviews or meta-analyses on the subject of hearing loss and dementia.

They therefore examined the literature themselves and looked for:

"high-quality papers as those that had followed a cohort of cognitively healthy people for at least 5 years, had an objective measure of peripheral hearing (pure-tone audiometry), had incident dementia as an outcome, and had adjusted for age and cardiovascular risk factors as potential confounding factors."

They found only 3 studies that met these criteria with follow up varying from 9 to 17 years.

They found a relative risk of 1.9 for hearing loss and dementia which is quite high.

(This means that having hearing loss almost doubles your risk of dementia).

Of even greater interest is a measurement they used called PAF - the Population Attributable Fraction which is 23% for hearing loss.

As they describe the PAF is:

"the percentage reduction in new cases over a given time if a particular risk factor were completely eliminated".

So this would suggest that 23% of new cases of dementia could be eliminated by preventing hearing loss.

This is amongst the highest for all the risk factors and is of particular interest because hearing loss is (in theory at least) preventable and perhaps easier to manage than other factors such as obesity.

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Why Would Hearing Loss Cause Dementia?

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The exact mechanism is still not understood. There are a number of theories:

1. There are common mechanisms (e.g. microvascular changes) that cause both dementia and hearing loss.

2. Hearing loss adds to greater "cognitive load" - further stressing an already overworked brain and leading to greater cell death.

3. Hearing loss increases social isolation and/or depression which are known to increase dementia risk themselves.

4. Auditory stimulation itself may have a protective effect against dementia.

It should be noted if point 1 is the main reason for the finding then it would make the process less modifiable or treatable.

The authors discuss this particularly in relation to central and peripheral hearing loss.

(Basically central means involving the brain, whereas peripheral means the inner and outer ear.)

You can potentially modify peripheral hearing loss with a hearing aid but you can't really do anything (as far as I know) for central hearing loss.

Obviously the best way to actually prevent hearing loss is to reduce exposure to loud noise and hence damage to the auditory components of the ear (particularly the cochlear hair cells).

Once it is established and the damage is done it is not reversible, but depending on the exact mechanism of how it relates to dementia, a hearing aid might be the next best thing.

This also brings us to one of the central problems in relation to hearing loss and dementia - i.e. the limited amount of research.

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The Problem

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As the authors of the commission report point out there is very little research in this field - possibly due to the fact that it is not widely known.

Further research is need to establish true causality i.e. that:

1. Hearing loss does in fact cause/contribute towards developing dementia (i.e. we are not just looking at correlation).

2. Hearing modification (e.g. hearing aids) can actually prevent or delay onset of dementia.

Right now we just don't have the research to confirm this.

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Conclusion

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Please check out the Lancet report if you have an interest in dementia.

It is 62 pages but the most important information is contained in the 2 page summary at the start.

I think these issues are important to consider for the whole of society.

In 2015 there were estimated to be about 47 million people living with dementia, the figure is expected to be 131 million by 2050!

Society is already struggling to look after these cases and such a huge rise will cripple most social and healthcare systems, not to mention the immense toll it will take on patients and their families.

It is therefore immensely useful to know what we can do to prevent this.

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References

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1. Livingston, Gill, Andrew Sommerlad, Vasiliki Orgeta, Sergi G. Costafreda, Jonathan Huntley, David Ames, Clive Ballard, et al. 2017. “Dementia Prevention, Intervention, and Care.” The Lancet, July. Elsevier. doi:10.1016/S0140-6736(17)31363-6.

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Thank you for reading

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