The Role of Photobiomodulation in Managing Sleep Disorders and Psychobehavioral Symptoms in Alzheimer’s Disease


Alzheimer’s disease (AD) is a progressive neurodegenerative disorder characterized by cognitive decline, psychobehavioral symptoms, and sleep disturbances [1]. Approximately 90% of AD patients develop psychobehavioral symptoms, contributing to increased caregiver burden and reduced patient quality of life [4,5].

Sleep disorders are also prevalent, affecting 70% of patients in the early stages of AD [7]. This article explores the potential of photobiomodulation (PBM) as a non-pharmacological therapy for managing sleep disorders and psychobehavioral symptoms in AD, backed by a comprehensive meta-analysis.

Sleep Disorders in Alzheimer’s Disease

The suprachiasmatic nucleus (SCN), a key regulator in the hypothalamus, plays a crucial role in synchronizing circadian rhythms [8]. In AD patients, neuropathic damage and reduced outdoor exposure contribute to decreased circadian rhythm stability [10]. Age-related eye defects further impact light transmission, exacerbating circadian rhythm and sleep disorders [11]. Sleep disruption in AD patients is a common occurrence, affecting 70% of individuals in the early stages [7].

Current Treatment Landscape for Alzheimer’s Disease

Pharmacological therapies, such as cholinesterase inhibitors, NMDA receptor antagonists, Aβ inhibitors, and intestinal flora modulators, are the primary treatments for AD [12]. While these medications may alleviate cognitive and memory impairments, they cannot halt disease progression or provide a cure.

Additionally, medication-related side effects, such as poor appetite and hallucinations, may occur in some patients [13–15]. The search for a highly efficacious treatment with minimal side effects remains a significant research challenge.

Photobiomodulation: A Deep Dive

Photobiomodulation (PBM), also known as low-level laser therapy (LLLT), is a non-invasive therapeutic modality that utilizes light within the red and near-infrared spectrum (600-1000 nm) to stimulate cellular processes and induce therapeutic effects. This light interacts with cellular structures, triggering a cascade of biochemical and physiological changes that promote healing, pain relief, and tissue regeneration.

Here’s a comprehensive breakdown of photobiomodulation:

What it does:

  • Enhances cellular energy production: PBM stimulates the production of adenosine triphosphate (ATP), the primary energy source for cells, leading to increased cellular activity and function.
  • Reduces inflammation: PBM modulates the inflammatory response by suppressing the production of inflammatory cytokines and promoting the production of anti-inflammatory mediators.
  • Promotes tissue repair and regeneration: PBM stimulates the proliferation and differentiation of stem cells, promotes angiogenesis (new blood vessel formation), and enhances collagen synthesis, all of which are essential for tissue repair and regeneration.
  • Reduces pain: PBM modulates pain perception by acting on pain receptors and pathways, leading to pain relief.

How it works:

  • Light absorption: When PBM light is applied to the skin, it is absorbed by chromophores within the cells, such as cytochrome c oxidase and mitochondrial cytochromes.
  • Photochemical reactions: The absorbed light energy triggers photochemical reactions within the cells, leading to the production of reactive oxygen species (ROS) and nitric oxide (NO).
  • Cellular signaling: ROS and NO act as signaling molecules, triggering various intracellular signaling pathways that ultimately lead to the therapeutic effects of PBM.

Clinical applications:

PBM is a versatile therapeutic modality with a wide range of clinical applications, including:

  • Pain management: PBM is effective in treating acute and chronic pain conditions, including musculoskeletal pain, neuropathic pain, and post-surgical pain.
  • Wound healing: PBM promotes wound healing by accelerating cell proliferation and tissue regeneration. It is used to treat various types of wounds, including diabetic foot ulcers, pressure ulcers, and burns.
  • Sports injuries: PBM can help athletes recover from injuries faster by reducing pain, inflammation, and muscle spasms.
  • Neurological disorders: PBM has shown promise in treating neurological disorders such as stroke, Parkinson’s disease, and Alzheimer’s disease.
  • Skin conditions: PBM is used to treat various skin conditions, including acne, psoriasis, and eczema.

Benefits of PBM:

  • Non-invasive and painless: PBM is a safe and gentle treatment modality with minimal side effects.
  • Effective for a variety of conditions: PBM can be used to treat a wide range of acute and chronic conditions.
  • Drug-free: PBM provides a drug-free alternative for pain relief and tissue repair.
  • Accelerated healing: PBM can help to accelerate the healing process for wounds and injuries.
  • Improved quality of life: PBM can improve the quality of life for individuals suffering from chronic pain or debilitating conditions.

Limitations of PBM:

  • Limited depth of penetration: PBM light only penetrates a few centimeters into the tissue, which limits its effectiveness for deep-seated conditions.
  • Variable efficacy: The effectiveness of PBM can vary depending on the specific condition being treated and the treatment parameters used.
  • Lack of standardization: There is a lack of standardization in PBM treatment protocols, which can make it difficult to compare results from different studies.

Future directions:

PBM is a rapidly evolving field with significant potential for future development. Research is ongoing to explore new applications for PBM, optimize treatment protocols, and develop new PBM devices.

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Photobiomodulation as a Non-Pharmacological Therapy

Photobiomodulation (PBM) emerges as a promising non-pharmacological intervention, utilizing light energy to modulate biological functions and promote therapeutic effects. PBM stimulates the SCN, regulating melatonin secretion and facilitating communication between the hypothalamus and cortex [16]. Recent studies have highlighted the potential of PBM in neurology, particularly in the treatment and regulation of neurodegenerative diseases [19]. PBM has shown promise in improving cognitive function, enhancing quality of life, and reducing caregiver burden by mitigating neuronal damage and inflammatory responses in AD patients [20].

The Need for a Comprehensive Meta-Analysis

Despite the growing interest in light therapy for AD, a systematic evaluation of its efficacy and safety is lacking. To address this gap, a comprehensive systematic review and meta-analysis are necessary to rigorously evaluate the effectiveness of light therapy in alleviating sleep disorders and psychobehavioral symptoms in AD patients.

Meta-Analysis Findings

A meta-analysis conducted by Van Maanen et al. [21] included studies with broad inclusion criteria, demonstrating the effectiveness of light therapy in treating sleep problems among AD patients. Roccaro et al. [22] conducted a systematic review specifically focusing on the impact of light therapy on circadian rhythm disturbances and sleep efficiency in AD patients, concluding that light therapy was effective in ameliorating these issues.

Moreover, prior studies have suggested that light therapy can reduce cognitive decompensation and depressive behavior in AD patients [23,24]. However, additional research is warranted to strengthen the limited evidence on its effectiveness. In comparison to earlier meta-analyses, our meta-analysis encompasses a larger number of articles and outcome metrics, expanding the sample size and exclusively including randomized controlled trials (RCTs) to reduce sampling error. Consequently, our meta-analysis aims to contribute robust evidence on the effectiveness of light therapy in treating sleep disorders and psychobehavioral symptoms in AD patients.


Alzheimer’s disease (AD) remains a formidable challenge in public health due to its progressive nature, irreversible brain injury, and significant impact on both patients and caregivers. As the fourth leading cause of mortality among older adults, AD necessitates urgent resolution [43].

Despite extensive research in pharmacological treatments, current interventions only offer limited relief from clinical symptoms and are incapable of halting or reversing the pathological process [45,46]. Moreover, the associated side effects, including diarrhea, muscle cramps, weakness, nausea, vomiting, and insomnia, contribute to reduced patient compliance, highlighting the need for alternative, more patient-friendly interventions [45,46].

The search for effective, safe, and well-tolerated interventions has led to the exploration of non-pharmacological treatments. Photobiomodulation (PBM) emerges as a promising candidate, offering a non-invasive treatment mechanism with minimal side effects. This chapter delves into the discussion surrounding the potential of PBM as an adjunct or preventive physiotherapy intervention for AD, as revealed through a systematic review and meta-analysis of 15 randomized controlled trials (RCTs).

The Advantages of Photobiomodulation

One of the primary advantages of PBM lies in its non-invasive nature, making it a favorable option for patients seeking alternatives to traditional pharmacological treatments. With its relative safety, low cost, and minimal side effects, PBM stands out as a modality that could enhance patient compliance and overall well-being.

Addressing Sleep Disorders and Psychobehavioral Symptoms

The meta-analysis of the 15 RCTs included in this study focused on evaluating the impact of PBM on sleep disorders and psychobehavioral symptoms in AD patients. The results demonstrated a positive effect of light therapy on sleep efficiency (SE), sleep quality, depressed mood, caregiver burden, and agitated behavior. These findings align with the growing body of evidence supporting the efficacy of PBM in neurodegenerative diseases, particularly in enhancing cognitive function and reducing inflammatory responses [20].

Significance of the Subgroup Analysis

To further explore the potential sources of heterogeneity in the results, a subgroup analysis was conducted. Notably, environmental factors, the degree of dementia, and the frequency of PBM sessions were considered as potential contributors to heterogeneity. Surprisingly, the analysis did not identify these factors as sources of variation, suggesting that the observed heterogeneity may be attributed to the limited number of included studies. This emphasizes the need for ongoing research efforts to expand the sample size and conduct multi-center clinical studies. Robust evidence derived from larger and more diverse cohorts will provide valuable insights into the specific conditions under which PBM is most effective.

Implications for Future Research and Clinical Practice

The promising results of this meta-analysis suggest that PBM could play a significant role in ameliorating sleep disorders and psychobehavioral symptoms in AD patients. However, it is crucial to acknowledge the limitations of the current body of evidence, including the relatively small sample size and potential publication bias. Future research endeavors should prioritize expanding the sample size, conducting multi-center trials, and addressing any publication bias to enhance the reliability and generalizability of the findings.


In conclusion, the discussion underscores the urgent need for effective and well-tolerated interventions for Alzheimer’s disease. The limitations of current pharmacological treatments, coupled with the adverse effects that compromise patient compliance, highlight the importance of exploring alternative approaches.

Photobiomodulation (PBM) emerges as a promising non-pharmacological intervention, offering relative safety, low cost, and minimal side effects. The meta-analysis of 15 randomized controlled trials provides encouraging evidence of PBM’s positive impact on sleep disorders and psychobehavioral symptoms in AD patients. However, the observed heterogeneity underscores the necessity for future research to expand the sample size and conduct multi-center studies, ensuring the robustness and generalizability of the findings. The implications of this discussion extend to both the research community and clinical practitioners, urging continued exploration of PBM’s potential in enhancing the quality of life for individuals affected by Alzheimer’s disease.

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