New Zealand researchers agree: hearing loss is probably a dementia risk factor

By Daniel Fink, MD, Chair, The Quiet Coalition

Many people don’t understand the process of medical and scientific research and how different hypotheses are developed and tested, using different methods in different human populations with animal studies when possible, until a consensus is reached. This was how researchers–including doctors, epidemiologists, researchers using animal models, and scientists doing basic research at the cellular, molecular, and genetic levels–figured out that cigarette smoke causes cancer and many other diseases, and how it does this. Despite the broad scientific and public health consensus, there are still skeptics, such as those at the conservative Heartland Institute, who say there is still doubt about whether smoking causes lung cancer. There is also a Flat Earth Society. Many Americans think that evolution is an unproven theory despite more than a century of research and strong evidence supporting evolution.

For the rest of us who believe in evidence-based science and evidence-based social and economic policies, our understanding of reality is always evolving based on the evidence. Sometimes something long thought to be true is found not to be correct after all. In medicine, one of the best examples may be ulcers in the stomach and small intestine, which for decades were thought to be caused by too much stomach acid but were found to be caused by bacteria. Australians Barry Marshall and J. Robin Warren won the Nobel Prize in 2005 for making this discovery. But most of the time an early hypothesis is confirmed by one study, and then another, and then by studies in animal models, and then by basic science research, until a broad consensus is reached.

This is what is happening with the hypothesis that hearing loss is associated, probably causally, with dementia. Dr. Frank Lin at Johns Hopkins University may be the best-known researcher in this field but other researchers in other countries are studying the same question. This report from New Zealand discusses what is being done there. And this report from the UK discusses research presented there.

It’s always good to have confirmation of research by different researchers using different techniques in different populations. Such confirmation helps validate initial findings in one population and helps move our understanding forward. We know that noise exposure causes hearing loss. If hearing loss is shown to be causally associated with the development of dementia, then preventing hearing loss should help to also prevent dementia. One theory is that the brain needs input to maintain function, and without auditory input and/or social connections, brain function declines. Another theory is that whatever degenerative process causes hearing loss also causes loss of mental function. Ongoing studies, providing hearing aids to those with hearing loss but not to others and then measuring intellectual function over time, may elucidate the cause-effect relationship. Regardless, we don’t need to wait for more evidence for the link. Preserving one’s hearing should be enough reason to avoid loud noise or to wear ear plugs if you can’t.

Dr. Daniel Fink is a leading noise activist based in the Los Angeles area. He serves on the board of the American Tinnitus Association, is the interim chair of Quiet Communities’s Health Advisory Council, and is the founding chair of The Quiet Coalition, an organization of science, health, and legal professionals concerned about the impacts of noise on health, environment, learning, productivity, and quality of life in America.

Comments (4)

  1. Janine Gliener

    I am curious – what about people who are deaf from birth? Do their brains suffer from lack of auditory input and do they become mentally ill? If not, why not?

    1. GMB (Post author)

      I’m not an audiologist, researcher, or medical doctor, so can’t answer the question. But I will note that the various papers and studies I’ve read about focus on social isolation as the primary factor with regard to hearing loss and dementia. People who are deaf from birth learn other ways to communicate. It is people who could formerly hear other people speak and engage in conversation, but who lose their hearing and become socially isolated who are at risk. With little engagement, social isolation apparently speeds up the course of dementia.

  2. Jan L. Mayes

    Hearing aid research confirmed years ago that hearing loss is a risk factor for dementia. Preventing hearing loss is important. But approx 10% of general population has hearing loss from non-preventable causes. Science has proven that using hearing aids drops dementia risk back to average. So a big question is, why aren’t 2 hearing aids covered by health/insurance plans? People wear eyeglasses, not monocles. The vast majority of people with hearing loss need 2 hearing aids to prevent higher dementia risk. Is it negligent 2 hearing aids aren’t covered given high cost of dementia to society? People with hearing loss should be protesting this especially since the body of scientific research on hearing loss and dementia is growing stronger with every new study.

    1. GMB (Post author)

      Private insurance doesn’t cover hearing aids b/c medicare doesn’t. Medicare should, but Medicare doesn’t cover ears, eyes, and teeth, three things that, if covered, would improve the quality of life of almost all older Americans. Also, the handful of hearing aid companies didn’t have incentive to make leaps with the technology and they can charge what they want, so they are really expensive. That is probably going to change soon, with hearing aids being available over-the-counter (and check out our piece on personal sound amplification products:


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