Buying time: a rationale for examining the use of circadian rhythm and sleep interventions to delay progression of mild cognitive impairment to Alzheimer's disease

Abstract

As of 2010, the worldwide economic impact of dementia was estimated at $604 billion USD; and without discovery of a cure or effective interventions to delay disease progression, dementia's annual global economic impact is expected to surpass $1 trillion USD as early as 2030. Alzheimer's disease (AD) is the leading cause of dementia accounting for over 75% of all cases. Toxic accumulation of amyloid beta (Aβ), either by overproduction or some clearance failure, is thought to be an underlying mechanism of the neuronal cell death characteristic of AD-though this amyloid hypothesis has been increasingly challenged in recent years. A compelling alternative hypothesis points to chronic neuroinflammation as a common root in late-life degenerative diseases including AD. Apolipoprotein-E (APOE) genotype is the strongest genetic risk factor for AD: APOE-ε4 is proinflammatory and individuals with this genotype accumulate more Aβ, are at high risk of developing AD, and almost half of all AD patients have at least one ε4 allele. Recent studies suggest a bidirectional relationship exists between sleep and AD pathology. Sleep may play an important role in Aβ clearance, and getting good quality sleep vs. poor quality sleep might reduce the AD risk associated with neuroinflammation and the ε4 allele. Taken together, these findings are particularly important given the sleep disruptions commonly associated with AD and the increased burden disrupted sleep poses for AD caregivers. The current review aims to: (1) identify individuals at high risk for dementia who may benefit most from sleep interventions; (2) explore the role poor sleep quality plays in exacerbating AD type dementia; (3) examine the science of sleep interventions to date; and (4) provide a road map in pursuit of comprehensive sleep interventions, specifically targeted to promote cognitive function and delay progression of dementia.

Keywords: Alzheimer’s; aging; bright light therapy; chronotherapy; circadian; dementia; mild cognitive impairment; sleep.

Figure 1

A simplified schematic of the proposed pathways associated with AD pathogenesis. The red arrows indicate possible pathways whereby circadian dysregulation and poor sleep might promote AD pathogenesis through proinflammatory mechanisms and increased accumulation and deposition of Aβ. According to this model, bidirectional relationships exist between circadian dysregulation and poor sleep; inflammation and Aβ deposition; and AD pathogenesis and circadiandysregulation.

Figure 2

A simplified schematic of the proposed interventions that may have potential to delay AD pathogenesis. The green arrows indicate pathways for improved circadian regulation and sleep quality, ultimately delaying AD pathogenesis. According to this model, chronobiotics (i.e., bright light therapy (BLT); melatonin; exercise; and food restriction) and good sleep hygiene could be used individually—but preferably in combination—to improve circadian regulation and sleep quality, decrease inflammation and Aβ deposition, and thereby delay AD pathogenesis.