Magical statistics: Hearing loss causes dementia

Magical thinking sees a meaningful, causal link between two things that happen to occur together or to look alike in some way. On this view, there are no actual coincidences, links owing purely to random chance: what might appear to be coincidences are actually linked in some manner that we do not understand; Carl Jung described them as “synchronous” and meaningful, not coincidental.

The Skeptic’s Dictionary gives many examples, as does Psychology Today.

What needs to be said is that much, most, or perhaps all of medical statistics is pervaded by magical thinking, the confusion of correlation with causation. For example, increasingly fashionable (or faddish?) emphasis on prevention is replete with references to “risk factors”, things that are “associated = correlated” with some condition. In short order, “risk factor” becomes confused with actual risk, and drug companies capitalize on this to sell drugs that claim to lower risks when actually they only affect risk factors: symptoms and not illnesses are being “treated”.

This deception inaugurated the era of “blockbuster” drugs, enormously profitable because they are taken lifelong: drugs to lower cholesterol, blood pressure, blood sugar and to increase bone density. But data on morbidity and mortality fail to detect any actual benefit from “statins, antihypertensives, and bisphosphanates” *, and anti-diabetes pills continue to be marketed at the same time as law firms carry on class-action suits because of the toxicities of those drugs, which have highly unpleasant ands sometimes deadly “side” effects including allergic reactions, bloating, diarrhea, flatulence, hypoglycemia, cardiovascular troubles, cholestatic jaundice, lactic acidosis, nausea, urinary tract infections, weight gain.

Blockbuster drugs rely on the confusion
of symptoms (risk factors)
with actual risks (causes),
exemplifying magical thinking
whereby actual harm is actually caused
to those who take the drugs

Another instance of magical thinking is the increasingly prominent insinuation that hearing loss leads to (causes) dementia.

The charge on this seems to be led by Dr. Frank Lin, MD, PhD, at Johns Hopkins University:
“Hearing Loss and Dementia Linked in Study
Release Date: February 14, 2011
Seniors with hearing loss are significantly more likely to develop dementia over time than those who retain their hearing, a study by Johns Hopkins and National Institute on Aging researchers suggests. The findings, the researchers say, could lead to new ways to combat dementia, a condition that affects millions of people worldwide and carries heavy societal burdens. Although the reason for the link between the two conditions is unknown, the investigators suggest that a common pathology may underlie both or that the strain of decoding sounds over the years may overwhelm the brains of people with hearing loss, leaving them more vulnerable to dementia. They also speculate that hearing loss could lead to dementia by making individuals more socially isolated, a known risk factor for dementia and other cognitive disorders.
Whatever the cause, the scientists report, their finding may offer a starting point for interventions — even as simple as hearing aids — that could delay or prevent dementia by improving patients’ hearing.”

This press release from Johns Hopkins gives the clear impression that hearing loss is a cause dementia. The last sentence also delivers the astonishingly nonsensical assertion that even if hearing loss is not the cause, treating it could have a beneficial effect on the risk of dementia!

Public media of course parrot this pseudo-scientific stuff. Most of the headlines as well as the texts of these pieces support the idea that hearing loss can lead to dementia:
“A 2011 study found that hearing loss may increase your chances of developing dementia”
“Johns Hopkins: Hearing problems lead to dementia”
“Hearing loss linked to dementia — Can getting a hearing aid help prevent memory loss?”
“Hearing loss speeds up brain shrinkage and could lead to dementia, researchers claim”
“The link between hearing loss and dementia — A new discovery gives you a new reason to check your hearing now”
“Straining to hear and fend off dementia”
“Could hearing loss and dementia be connected?”

Manufacturers of hearing aids jumped on the bandwagon:
“Hearing loss is now linked to Alzheimer’s disease and dementia.
According to several major studies, older adults with hearing loss are more likely to develop Alzheimer’s disease and dementia, compared to those with normal hearing. Further, the risk escalates as a person’s hearing loss grows worse. Those with mild hearing impairment are nearly twice as likely to develop dementia compared to those with normal hearing. The risk increases three-fold for those with moderate hearing loss, and five-fold for those with severe impairment.
Specifically, the risk of dementia increases among those with a hearing loss greater than 25 decibels. For study participants over the age of 60, 36 percent of the risk for dementia was associated with hearing loss.
How are the conditions connected?
Although the reason for the link between hearing loss and dementia is not conclusive, study investigators suggest that a common pathology may underlie both”

Also on the bandwagon is a local Speech & Hearing Center.  From an“Ask the experts” page of SENIORS GUIDE magazine:
“Researchers have shown a strong correlation between un-treated hearing loss (i.e., having hearing loss and not wearing hearing aids) and dementia. A study completed by Dr. Lin and colleagues at Johns Hopkins and the National Institute for Communicative Disorders revealed that for every one year an individual with a mild hearing loss went without hearing aids, there was a seven year cognitive decline”.
That’s quite an extension and distortion of the published study.
That published scientific article is Lin et al., “Hearing Loss and Incident Dementia”, Archives of Neurology, 68 (2011) 214–20. Its stated conclusions are that “Hearing loss is independently associated with incident all-cause dementia. Whether hearing loss is a marker for early stage dementia or is actually a modifiable risk factor for dementia deserves further study.”
Unwary readers might take the first sentence as meaning that hearing loss does cause dementia. The second sentence makes the mistake of confusing risk factor with risk and adds to the impression of a causative link.

“[H]earing loss was independently associated with incident all-cause dementia after adjustment for sex, age, race, education, diabetes, smoking, and hypertension, and our findings were robust to multiple sensitivity analyses. The risk of all-cause dementia increased log-linearly with hearing loss severity, and for individuals >60 years in our cohort, over one-third of the risk of incident all-cause dementia was associated with hearing loss.”

Lay readers might again be inclined to take these comments as supporting a causative link. But “independently associated” means only that these particular variables were fed into a computer program looking for degrees of association. Considerable uncertainty remains because of possible effects of other variables not taken into account, notably history of health, diet, and exercise, all of which are likely to be very influential on the rate of age-related deterioration; and there are obvious uncertainties associated with the manner in which education, smoking, hypertension were coded.

But bear in mind the inescapable fact that the probabilities of every type of organ failure and physiological dysfunction increase with age. Age is indubitably independently associated with hearing loss, dementia, diabetes, hypertension, as well as cancer, kidney failure, lung disease, etc.
Hearing loss is independently associated with age.
Dementia is independently associated with age.

It would take more than this study to make a plausible let alone convincing case for hearing loss as a potential cause of dementia. The original article actually spells out quite well the uncertainties that ought to stop speculation about causation, but it steps back from those sound observations to speculate about possible causative mechanisms: “exhaustion of cognitive reserve, social isolation, environmental deafferentation [presumably meaning deficiency of environmental stimuli], or a combination of these”. None of those appears to be amenable to study in any potentially convincing manner.

By contrast, direct evidence from the people studied is waved aside: “self-reported hearing aid use was not associated with a significant reduction in dementia risk”.
The researchers measured the dementia risk in this prospective study, that was not a subjective assessment by the people in the study. They could surely, however, be regarded as largely reliable in their testimony as to use or non-use of hearing aids.
The conclusion is clear: hearing aids did not help to avoid dementia among the people studied.
However, this ugly fact might destroy the hypothesis and impede ongoing research, so reasons are offered for ignoring it: “data on other key variables (e.g. type of hearing aid used, hours worn per day, number of years used, characteristics of subjects choosing to use hearing aids, use of other communicative strategies, adequacy of rehabilitation, etc) that would affect the success of aural rehabilitation and affect any observed association were not gathered. Consequently, whether hearing advices [sic; should perhaps be devices?] and aural rehabilitative strategies could have an effect on cognitive decline and dementia remains unknown and will require further study”.

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*  Järvinen et al., “The true cost of pharmacological disease prevention”, British Medical Journal, 342 (2011) doi: 10.1136/bmj.d2175