Journal of Sleep Disorders: Treatment and CareISSN: 2325-9639

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Editorial, J Sleep Disor Treat Care Vol: 5 Issue: 1

Lighting the Way to Better Sleep and Health

Killgore WDS*
Department of Psychiatry, University of Arizona, Social, Cognitive, and Affective Neuroscience Laboratory, USA
Corresponding author : Killgore WDS, PhD
Department of Psychiatry, University of Arizona, Social, Cognitive, and Affective Neuroscience Lab, McLean Hospital, Harvard Medical School, 115 Mill Street, Belmont, MA 02478, USA
Tel: (617) 855-3166; Fax: (617) 855-2770
E-mail: [email protected] mclean.harvard.edu
Received: March 05, 2016 Accepted: March 05, 2016 Published: March 10, 2016
Citation: Killgore WDS (2016) Lighting the Way to Better Sleep and Health. J Sleep Disor: Treat Care 5:1. doi:10.4172/2325-9639.1000e104

Abstract

Few of us would say we routinely get enough sleep. Typical sleep duration has reportedly declined over the past half-century or so, probably due to the myriad changes in work and lifestyle that have emerged with our increased reliance on electronic technology. This is problematic, as sleep is critical to so many of our cognitive functions and health. Sleep facilitates memory consolidation, emotional regulation, decision-making and judgment and maintains normal levels of alertness and focus throughout the day. In addition to its effects on cognitive functions, sleep is important for many aspects of physical health and brain repair. During sleep, the brain rids itself of neurotoxins increases the number of brain repairing oligodendrocytes and replenishes depleted energy reserves. Without adequate sleep, people are prone to a host of health related problems, including inflammation, weight gain, and high blood pressure. But while it is easy to point out the problems associated with disrupted or curtailed sleep, it is much less clear how to intervene to improve people’s sleep-wake cycles. Can anything be done to get us back on track?

Keywords: Better Sleep; sleep duration; sleep-wake cycles

Few of us would say we routinely get enough sleep. Typical sleep duration has reportedly declined over the past half-century or so, probably due to the myriad changes in work and lifestyle that have emerged with our increased reliance on electronic technology. This is problematic, as sleep is critical to so many of our cognitive functions and health. Sleep facilitates memory consolidation [1], emotional regulation [2], decision-making and judgment [3,4], and maintains normal levels of alertness and focus throughout the day [5]. In addition to its effects on cognitive functions, sleep is important for many aspects of physical health and brain repair. During sleep, the brain rids itself of neurotoxins [6], increases the number of brain repairing oligodendrocytes [7], and replenishes depleted energy reserves [8]. Without adequate sleep, people are prone to a host of health related problems, including inflammation [9], weight gain [10], and high blood pressure [11]. But while it is easy to point out the problems associated with disrupted or curtailed sleep, it is much less clear how to intervene to improve people’s sleep-wake cycles. Can anything be done to get us back on track?
While there are many pharmacologic and behavioral treatments that can have an impact on sleep, emerging evidence suggests that one natural and particularly powerful method for influencing sleep and wakefulness is by regulating light exposure. The 24-hour lightdark cycle is remarkably ingrained within our biology, and efforts to resist its influence are often met with reduced cognitive performance, emotional disruption, and deleterious health related consequences [12]. In particular, exposure to the blue wavelengths of light has a powerful effect on the circulating plasma levels of melatonin, a hormone secreted by the pineal gland and which plays a major role in regulating the sleep-wake cycle [13]. Melatonin levels are normally depressed during daylight hours, but increase dramatically during the evening as blue light levels fade with the setting of the sun. This natural rhythm, however, is being increasingly disrupted by our routine exposure to artificial light sources that emit blue wavelength light at times that are out of phase with our normal circadian rhythms, potentially affecting sleep and health [14]. A recent study showed that even the blue light emitted from a standard eBook reader before bedtime was enough to suppress evening melatonin onset, reduce feelings of sleepiness, and make it harder to fall asleep, disrupt sleep architecture, and lead to reduced alertness the following day [15]. The problem is not that blue light is, in and of itself, bad or somehow inherently unhealthy. Rather, the problem is the timing of the light exposure. In fact, recent research suggests that blue light exposure— when applied at the right points in the circadian phase—can enhance cognitive functioning and improve sleep [16]. The timing of the light exposure is what is most critical. Morning exposure to blue light appears to phase advance the circadian rhythm through its influence on the melanopsin photosensitive cells of the retina, which project to the suprachiasmiatic nucleus of the hypothalamus, the brain’s primary clock system. This suppression of melatonin leads to greater alertness during the day and an earlier onset of sleep in the evening, whereas exposure to the same levels of blue light in the evening can delay the normal rhythmic onset of sleep [16]. Interestingly, getting more blue light in the daytime can actually protect individuals from the adverse phase shifting effects of blue light on sleep in the evening [17]. Timing can be controlled in simple ways, such as getting some sunlight in the morning, the use of artificial light boxes, strategic donning of blue blocking glasses in the evening [18] and perhaps through the use of other spectrum shifting technologies or shields for electronic screens. With guidance from empirical data, we are now at the forefront of being able to use light to regulate our sleep and perhaps even enhance performance.
Although promising, research on the effects of light on sleep and wakefulness is still in its infancy. This remains a vast unexplored research frontier and many questions have yet to be examined— yet few investigators are working on the problem. Recent evidence suggests that light may prove to be a particularly well-accepted and cost effective method for influencing sleep and alertness, and one that could be smartly designed into environmental systems. Interestingly, recent research now suggests that there may be additional effects of light on cognition that are exclusive of its effects on melatonin. For instance, even a single brief half-hour exposure to blue light may affect working memory and emotion regulation systems in the brain [19]. The effects of light beyond the circadian system remain to be clarified and this is destined to be a fruitful area of research. Additionally, light may have beneficial therapeutic effects on a variety of health-related problems, such as in the recovery process from concussion. Recent findings suggest that a 4-week exposure to blue wavelength light for 45 minutes each day was able to reduce fatigue and daytime sleepiness in people recovering from mild traumatic brain injury [20]. Given that sleep enhances the proliferation of myelin forming oligodendrocytes, could the improved sleep from light therapy lead to more rapid recovery from injury? Similarly, while light exposure has been used to help people with seasonal affective depression, virtually nothing is known about how similar light treatment regimens might affect other emotional conditions such as post-traumatic stress disorder (PTSD). Even less is known about how other wavelengths of light, such as red, amber, green, or violet might affect normal and pathological brain functioning, but preliminary findings raise intriguing possibilities that light may affect many more brain systems than just those involved in melatonin regulation [21]. Many questions remain to be answered: Who is most responsive to light exposure and why? Which wavelengths of light are most effective and for what aspects of sleep, wakefulness, cognition, and health? What brain systems are affected by particular wavelengths? What are the optimal timings and dosages for light? To what extent do light exposure effects rely upon the suppression of melatonin versus activation of more immediate neural systems? Is the effect of light exposure cumulative and can it be banked to permit later resistance to sleep loss? Can light exposure during sleep be used to fine tune sleep architecture? It will be critical to determine the answers to these questions in the coming years. There appears to be great potential for the use of light therapy in treating problems associated with sleep and wakefulness, and perhaps even brain repair and trauma recovery, but intensive research is necessary. The field of “light and sleep” is particularly ripe for deeper scientific exploration.

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