Home Mind & Brain Sensory Loss in Midlife Significantly Increases Risk of Dementia, New Study Reveals

Sensory Loss in Midlife Significantly Increases Risk of Dementia, New Study Reveals

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A recent study from Newcastle University that was published in The Neuroscientist shows a strong correlation between sensory loss in middle age and an increased risk of dementia later in life. The study explores the connections between olfactory, visual, and hearing impairments and the risk of dementia, including Alzheimer’s disease (AD), vascular dementia (VaD), and Lewy body disease (LBD).

The research underscores a robust relationship between sensory impairments and dementia, stressing that this correlation is not merely due to the common occurrence of both conditions in ageing populations. Instead, the findings suggest that sensory loss might be an early indicator or contributing factor to cognitive decline.

Olfactory, visual, and hearing impairments are all associated with an increased risk of subsequent dementia. The reasons for this are unclear, but the link is strong and not due to the simple co-occurrence of two common conditions in ageing.

Olfactory deficits are particularly highlighted as a potential early marker for neurodegenerative diseases. The study draws attention to the significant role olfactory dysfunction plays in diseases such as Parkinson’s disease (PD) and LBD, where it often precedes motor symptoms by nearly a decade. For Alzheimer’s disease, olfactory impairments have been linked to neuropathological changes, such as neurofibrillary tangles and amyloid-beta plaques, found in the olfactory bulbs and related brain regions.

Identifying smells has been found to be a useful screening tool that can predict the progression from mild cognitive impairment (MCI) to Alzheimer’s disease (AD) dementia. This means that early detection through olfactory testing could be key to managing dementia and maybe even slowing it down.

Visual impairments, which are expected to affect 1 billion people by 2050, have also been linked to an increased risk of dementia. The study examines various age-related eye diseases and their connections to cognitive decline. It emphasises the importance of treating visual impairments to potentially reduce dementia risk. For instance, cataract surgery was associated with a lower risk of developing dementia, indicating that improving vision might have protective effects against cognitive decline.

Reduced visual input from the eye can also cause structural changes in and around the primary visual cortex, which recovers on treatment, highlighting the need for further research to understand how these changes might influence dementia risk.

Hearing loss, particularly in midlife, is another sensory impairment significantly associated with an increased risk of dementia. The study discusses the mechanisms through which hearing loss might contribute to cognitive decline, such as reduced cognitive reserve and increased brain activity required for speech-in-noise perception, which may compete with other cognitive resources.

The research also points out that hearing loss may interact with neurodegenerative processes in the medial temporal lobe, a key area involved in auditory processing and implicated in Alzheimer’s disease. This interaction could exacerbate cognitive decline, making hearing loss a crucial factor in understanding and addressing dementia risk.

The study also explores the compounded effects of impairments in multiple sensory domains, which may lead to faster cognitive decline than unisensory impairment alone. For example, the Blue Mountains Eye Study found that dual sensory impairment was linked to a more rapid decline in cognitive function compared to visual or hearing impairment alone.

Poor multisensory composite scores were recently associated with an increased risk of all-cause dementia, emphasising the need for comprehensive assessments of sensory functions in ageing populations to better predict and manage dementia risk.

The findings of this study open new avenues for research and potential interventions. The authors call for further studies to investigate the neurobiological mechanisms underlying the link between sensory loss and dementia. They advocate for the development of sensory manipulation strategies as a means to delay or prevent the onset of dementia.

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