If someone told you there was a single modifiable health factor that accounts for more dementia risk than smoking, physical inactivity, or high blood pressure, you would probably want to know what it is — and what you can do about it.

According to the 2024 Lancet Commission on Dementia Prevention, Intervention, and Care, that factor is untreated hearing loss.

The Lancet Commission Finding That Changed How We Think About Hearing

The Lancet Commission on Dementia is a panel of the world's leading dementia researchers, and their reports — published in 2017, 2020, and most recently in 2024 — represent the most authoritative synthesis of dementia prevention science available. In their 2024 update, the Commission identified 14 modifiable risk factors for dementia. Hearing loss ranked as the largest single modifiable risk factor from midlife onward.

The numbers behind this finding are significant: addressing untreated hearing loss could prevent up to 7% of dementia cases globally — more than any other single preventable factor on the list. For context, smoking accounts for approximately 5% of attributable risk, and physical inactivity accounts for approximately 2%.

The research also identified a dose-response relationship: every 10 decibel decrease in hearing ability increases dementia risk, a finding consistent across four independent studies reviewed by the Commission. The relationship between hearing loss and cognitive decline is not a coincidence of aging. It is a biological connection with identifiable mechanisms.

Why Does Hearing Loss Affect the Brain?

Researchers have proposed several mechanisms explaining the connection between hearing loss and cognitive decline, and the evidence suggests more than one may be operating simultaneously.

The cognitive load hypothesis holds that when the brain must work significantly harder to process degraded sound, it diverts cognitive resources away from memory and executive function. Over years and decades, this chronic reallocation of mental effort leaves less capacity for higher-order thinking — accelerating cognitive decline that was once attributed simply to aging.

Social isolation offers a second pathway. Hearing loss frequently causes individuals to withdraw from conversations, avoid social gatherings, and disengage from the relationships that keep the brain cognitively active. Social isolation is itself an independent risk factor for dementia — and untreated hearing loss is one of the most common drivers of isolation in older adults.

A third mechanism involves direct neurological change. When the auditory cortex receives reduced stimulation over time, measurable structural changes occur in the brain — including accelerated atrophy in regions responsible for memory and language processing. Imaging studies have demonstrated that people with untreated hearing loss show faster rates of whole-brain volume loss compared to those with normal hearing.

The ACHIEVE Trial: What Happened When People Were Treated

The most compelling evidence for intervention comes from the ACHIEVE trial — the Aging and Cognitive Health Evaluation in Elders study — a large, multicentre randomized controlled trial published in The Lancet. Researchers assigned older adults with hearing loss to either a hearing intervention group or a health education control group and followed them over three years.

Among participants at higher baseline risk for cognitive decline, the hearing intervention group showed a 48% reduction in the rate of cognitive decline compared to the control group. The intervention was hearing aids — not a pharmaceutical, not a surgical procedure, not a lifestyle program requiring significant behavior change. Simply treating hearing loss with properly fitted hearing aids was enough to meaningfully slow the trajectory of cognitive decline in the population most at risk.

The ACHIEVE findings reinforce what audiology has long understood clinically: hearing aids are not cosmetic devices. They are medical interventions with measurable neurological benefit that extends far beyond the ability to follow conversation.

Who Should Be Paying Attention to This Research?

Hearing loss affects approximately 68% of adults in the United States aged 70 and older — and the vast majority go undiagnosed and untreated for years. The average person waits seven years between first noticing hearing difficulty and seeking professional evaluation. During those years, the cognitive consequences of untreated hearing loss accumulate.

The Lancet Commission's identification of midlife hearing loss as the leading modifiable risk factor is particularly significant because it suggests the relevant window for intervention begins earlier than most people assume. Adults in their 40s and 50s with noise-induced hearing loss, occupational hearing damage, or even mild age-related hearing loss are already in the window where hearing health decisions carry long-term cognitive implications.

Signs that a hearing evaluation may be overdue include frequently asking people to repeat themselves, difficulty following conversation in noisy environments, turning up the television volume higher than others prefer, feeling mentally fatigued after conversations that require sustained listening, avoiding social situations because of difficulty hearing, or family members expressing concern about your hearing.

What a Proper Hearing Evaluation Establishes

A comprehensive hearing evaluation with a Doctor of Audiology is not a simple pass/fail screening. It establishes a complete audiological baseline — documenting the precise configuration of your hearing across all frequencies, identifying the type and degree of any loss present, and determining whether hearing aids are indicated and what level of amplification would be appropriate.

This baseline is important independent of whether hearing aids are needed immediately. It creates a reference point against which future changes can be measured — allowing earlier identification of progression and earlier intervention when it matters most for cognitive health.

If hearing aids are recommended, the standard of care requires real ear measurement verification — a protocol that confirms the devices are programmed to deliver the correct amplification for your specific ear canal anatomy and audiogram. Studies consistently show that fewer than one in five audiology practices use real ear measurement routinely. At Haynie Audiology & Hearing Associates, real ear measurement is included with every hearing aid fitting as a clinical standard, not an optional add-on.

The Bottom Line

The 2024 Lancet Commission's findings are a clear call to action. Hearing loss is not an inevitable and inconsequential part of aging — it is the single largest modifiable risk factor for dementia identified by the world's leading dementia researchers, and it is treatable.

The ACHIEVE trial demonstrated that properly fitted hearing aids can reduce the rate of cognitive decline in high-risk individuals by nearly half. That evidence places hearing care alongside blood pressure management and physical activity as one of the most impactful preventive health decisions an adult can make for their long-term brain health.

If you are in Monmouth County and have been putting off a hearing evaluation, this is the research that should change that. Dr. Alexandra Haynie, Au.D., CCC-A, ABA provides comprehensive hearing evaluations at 31 West Main Street in downtown Freehold — with no referral required and Wednesday through Saturday appointment availability.