A comorbidity is an additional or secondary disease that an individual may have. Many individuals with Alzheimer’s and other causes of dementia are living with multiple comorbidities that are often underdiagnosed.
In a population-based study from 2017, it was found that 91.8% of individuals living with dementia also have another health condition, with 13.2% having one condition, 33.8% having two or three conditions, 27.8% having four or five conditions, and 16.9% having six or more conditions.
Both clinical and molecular studies suggest that chronic diseases may be associated with an increased risk of Alzheimer’s disease in different populations. While the causes of disease comorbidities in Alzheimer’s are not yet fully understood, disruptions such as inflammation in several shared biological pathways have been proposed to be the underlying mechanism for this occurrence.
Below, we detail four common disease comorbidities in Alzheimer’s disease and the importance of early and frequent neurocognitive testing for individuals with diseases associated with an increased risk of developing Alzheimer’s disease.
Disease comorbidities in Alzheimer’s disease significantly affect the clinical management of people living with Alzheimer’s. Many disease comorbidities in Alzheimer’s are associated with poor prognosis in those with Alzheimer’s. Identifying and addressing the presence of comorbid diseases early is critical for providing robust, personalized care and treatment.
Below, we outline four common disease comorbidities in Alzheimer’s disease.
Approximately 30% of adults aged 65 and older and 55% older than 80 years show some degree of hearing loss. The number of individuals impacted by age-related hearing loss is estimated to grow to 580 million worldwide by 2050.
In a study that tracked more than 600 adults for almost 12 years, researchers found that hearing loss correlated strongly with the development of dementia. Mild hearing loss doubled dementia risk, moderate hearing loss tripled the risk, and those with severe hearing impairment were five times more likely to develop dementia.
In 2020, an estimated 596 million individuals worldwide were living with an untreated distance vision impairment, 43 million of whom were blind.
Recent studies have suggested there is an association between vision loss and cognitive impairment. While findings from recent studies are currently limited by sample size, their results suggest that visual impairment may be a risk factor for dementia. In a cohort study of 1,061 women, baseline visual impairment was associated with a two- to five-fold increased risk of developing dementia over a median 3.8 years of follow-up. More severe visual impairment was associated with an increasingly elevated risk of incident dementia.
According to the World Health Organization, type 2 diabetes affects 422 million individuals worldwide and is the most prevalent metabolic disease. Type 2 diabetes is a well-established risk factor for Alzheimer’s disease, and the association between the two has been studied in depth.
One 2019 study found that diabetes was associated with a 1.25 to 1.9-fold increase in cognitive impairment and dementia. Another 2019 study suggests that diabetes and prediabetes are associated with accelerated cognitive impairment.
Well-established links to the development of Alzheimer’s and other causes of dementia include cardiovascular diseases such as cerebrovascular disease as well as risk factors for cardiovascular diseases such as hypertension and diabetes. Cerebrovascular disease and Alzheimer’s disease share risk factors in addition to overlapping neuropathology.
One study found that elevated blood pressure in midlife was associated with the development of neuritic plaques and neurofibrillary tangles present in Alzheimer’s disease. Another study demonstrated that the use of antihypertensive drugs was associated with a lower incidence of Alzheimer’s disease.
Hearing loss, vision loss, diabetes, hypertension, and cerebrovascular disease are widely prevalent diseases and conditions worldwide. As significant risk factors for developing Alzheimer’s-related dementia and other causes of dementia, individuals with these diseases must receive early and frequent neurocognitive testing. Early and frequent testing allows for the earliest possible identification of cognitive impairment, enabling early intervention and providing the ability to develop detailed, personalized care plans for those living with Alzheimer’s disease.
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