Obstructive Sleep Apnoea (OSA) and Dementia: A Summary

Author: Professor Ram Dhillon

An Apnoea is essentially a nocturnal strangulation, due to blockage of the upper breathing passages, for a minimum of 10 seconds, but it could be more: 15, 20, 30, or 40+ seconds. If an individual has 5 or more of these episodes per hour during sleep, the disorder Obstructive Sleep Apnoea is present. Mild OSA is 5-15 apnoeas per hour; Moderate OSA is 15-30 apnoeas per hour and severe is 30+ apnoeas per hour. This is called the AHI score/index and is a grading system of severity.

Obstructive Sleep Apnoea is associated with obesity, diabetes (type 2), heart disease, and dementia, amongst many other disorders. These associations are due to the metabolic and physiological consequences of the strangulation/apnoea, and, in many individuals, the low blood oxygen levels that can accompany each episode.

Obstructive Sleep Apnoea affects ~ 4-8% of the population. In the UK between 2.4-4.8 million, India: is mainly confined to the upper and middle classes with an estimated 35 million affected, and in the USA about 30 million. In the Middle East, Emirates, the local population risk is about 22% of the population. In China, the prevalence is about 12%, so 140 million people are affected, and generally the Chinese exhibit a lower BMI score.

Individuals with established OSA should be managed with proper medical assessment (a sleep study) and management, which would be lifestyle changes (which are hard to implement and maintain) but also consider interventions such as Mandibular Advancement Devices (MADs) and CPAP (Continuous Positive Airway Pressure).

Over the past few decades, growing evidence has suggested a link between Obstructive Sleep Apnoea and various cognitive impairments, including dementia.

In the UK there are ~ 1 million individuals with diagnosed dementia. It is estimated that ~33% have OSA.

In the UK if an individual falls into a category of dementia, moderate/severe, then the estimated health and social care costs are ~ £35K per annum. Hence preventing/delaying this need, for those with associated OSA, say for 3000 individuals with dementia for 2 years would save ~£52.5 million each year. The ongoing cost of the key management, CPAP (continuous positive airway pressure), is ~£1500 per annum so and overall saving per year of £48 million per year.

Well over a decade ago, Yaffe et al (2011) established that OSA is associated with an increased risk of cognitive decline and dementia. This study followed 298 older women for up to five years. The study found that women with sleep-disordered breathing, characterized by frequent apnoeas and hypopneas, were more likely to develop mild cognitive impairment or dementia compared to those without sleep-disordered breathing.

The mechanism of OSA contributing to dementia is intermittent hypoxia (low oxygen). The oxygen levels in the blood can plummet during repeated episodes of airway obstruction/apnoea/strangulation. Chronic intermittent hypoxia has been shown to cause oxidative stress and inflammation, leading to neuronal injury and brain tissue damage. A study by Lim et al. (2013) published in the journal “Sleep” demonstrated that patients with severe OSA had higher levels of inflammatory markers, such as C-reactive protein and interleukin-6, compared to those without OSA. These inflammatory processes are believed to contribute to the development of neurodegenerative diseases, including Alzheimer’s disease/dementia.

Fragmented sleep, where the required durations of the levels of sleep are disrupted, is also implicated in the relationship between OSA and dementia. The sleep fragmentation and subsequent non-refreshing sleep undermine the G lymphatic system of the brain leading to an impairment of the brain’s ability to clear amyloid-beta, a protein that accumulates in the brains of individuals with Alzheimer’s disease.

In addition to the pathological mechanisms linking OSA and dementia, several studies have highlighted the impact of OSA treatment on cognitive function. Continuous positive airway pressure (CPAP) therapy, the gold standard treatment for OSA, has been shown to improve cognitive outcomes in individuals with OSA. A randomized controlled trial by Ancoli-Israel et al. (2008) published in the American Journal of Respiratory and Critical Care Medicine investigated the effects of CPAP treatment on cognitive function in patients with Alzheimer’s disease and OSA. The study found that CPAP therapy significantly improved attention, verbal learning, and memory in these patients, suggesting that effective treatment of OSA can mitigate cognitive decline.

Worryingly, emerging research has indicated that the relationship between OSA and dementia may be bidirectional. Not only does OSA increase the risk of cognitive impairment, but cognitive decline and dementia may also exacerbate OSA symptoms. A study by Osorio et al. (2015) published in Neurology found that individuals with Alzheimer’s disease exhibited more severe OSA compared to cognitively normal older adults. The researchers hypothesized that neurodegenerative changes in brain regions regulating sleep and respiration could worsen OSA severity, creating a vicious cycle of cognitive decline and sleep-disordered breathing.

In summary, there is substantial evidence supporting the relationship between obstructive sleep apnoea (OSA) and dementia. Intermittent hypoxia, sleep fragmentation, and inflammation are key mechanisms through which OSA may contribute to cognitive impairment and the development of neurodegenerative diseases. Treatment of OSA with CPAP therapy has shown promise in improving cognitive function, highlighting the importance of early diagnosis and management of OSA in individuals at risk of dementia.

Additionally, the bidirectional nature of this relationship underscores the need for comprehensive care that addresses both sleep and cognitive health in older adults. As research continues to unravel the complexities of this relationship, it is crucial to raise awareness about the impact of OSA on cognitive function and to promote strategies for its effective management to enhance the quality of life for individuals affected by both conditions.

Some stark statistics

Individuals, over 65 years of age, are diagnosed with dementia. With an ageing population, this is expected to grow rapidly:
UK: 1 million
USA: 6.7 million
India: 8.8 million
Saudi Arabia: 1.8 million

WHO: worldwide ~55 million (2020) projected to rise to 78 million by 2030.

In the one-third of individuals with dementia who have OSA, the latter diagnosis and management will significantly enhance personal/family quality of life AND reduce the financial burden.

FINALLY: Do you have Sleep Apnoea? Use the attached “Modified STOP BANG” triage questionnaire

LISTEN TO THIS PODCAST: The Hidden Dangers of Untreated Sleep Apnoea with Professor Ram Dhillon

For more information on Obstructive Sleep Apnoea and Snoring, visit ENT London.