Light therapy associated with improved sleep and psychobehavioural symptoms in Alzheimer’s disease

A meta-analysis of 15 randomized controlled trials (RCTs) finds that light therapy significantly improves sleep efficiency, alleviates depression and reduces agitation in patients with Alzheimer’s disease (AD), as well as lessens caregiver burden.

Patients with AD may experience less light input compared with unaffected individuals due to limited outdoor exposure and poor light sensitivity owing to neuropathic damage as well as age-related eye defects (eg, macular degeneration and cataracts), which can lead to decreased circadian rhythm stability and ultimately, sleep disorders. [Cochrane Database Syst Rev;2014:CD003946; Br J Ophthalmol;2008:1439-1444] Disturbed sleep is reported in approximately 70 percent of AD patients and is associated with considerable caregiver burden. [Geriatr Nurs 2018;39:60-65]

Photobiomodulation (PBM) is a nonpharmacological therapy that uses light energy to stimulate suprachiasmatic nucleus (SCN), an area of the brain responsible for sleep regulation. [Mol Neurodegener 2022;17:35] Earlier studies have also indicated that PBM can improve cognitive function, enhance quality of life and reduce caregiver burden in patients with AD by reducing neuronal damage and inflammatory response. [Photobiomodul Photomed Laser Surg 2019;37:159-167; Alzheimers Res Ther 2022;14:84]

The present meta-analysis included 15 RCTs in older adults (n=598; age range, 65–80 years) with AD who had undergone light therapy or received usual care and were not regular users of antidepressants or sleeping pills. [PLoS One 2023;18:e0293977]

“While cognitive decline represents the most prominent clinical manifestation of AD, it is often accompanied by sleep disturbances and varied psychobehavioural symptoms, including apathy and depression as well as agitated behaviour characterized by exaggerated motor activity and verbal and/or physical aggression,” wrote the researchers. [Curr Psychiatry Rep 2019;21:66; Front Neurol 2021;12:644317]

Sleep efficiency (SE), defined as total sleep time divided by average time spent in bed, which translates into sleep quality, was included as an outcome measure of nine RCTs used in the meta-analysis. Pooled results of these studies indicated that light therapy had a significantly greater effect in terms of improving SE vs usual care (p<0.00001).

Cornell Scale for Depression in Dementia scores were reported in three of the studies. Meta-analysis findings revealed that light therapy could alleviate depressive symptoms in patients with AD to a greater degree than usual care (p<0.00001).

According to Cohen-Mansfield Agitation Inventory scores, which were reported in four of the RCTs, light therapy was more beneficial than usual care for improving agitated behaviour in patients with AD (p<0.00001).

Analysis of Zarit Caregiver Burden Interview scores, which measure adverse health outcomes experienced by caregivers of individuals with debilitating conditions and were employed in three of the studies, indicated that light therapy significantly reduced caregiver burden compared with usual care (p<0.00001).

“Overall, our current systematic review suggests that light therapy is more effective at improving sleep and psychobehavioural symptoms in patients with AD compared with usual care. However, most included studies involved small sample sizes, with varying degrees of light intensity and therapy duration. Thus, larger multicentre RCTs are required to determine optimal light therapy protocol for AD patients,” concluded the researchers.