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EnLightening Treatments: Light and Our Circadian Rhythms

By Rose Cytryn

In its preamble, the World Health Organization defines health as a “… state of complete physical, mental, and social well-being and not merely the absence of disease or infirmity”1. In defining health in this way, the treatment of patients is evolving from curing a patient’s physical disease, to acknowledging the psychological and emotional weight caused by an illness and the potential ramifications of this. An increasing number of art and music therapy programs are being put into use in an attempt to treat the non-physical well-being of patients. Studies look to light as a critical aspect of the human existence to understand more about the way patient’s experiences are influenced by outside factors. Natural light, bright light therapy or exposure, as it is referred to in many studies, is related not only to sleep related illnesses, but depressive disorders as well as cancer symptoms. The change in, and duration of light exposure, naturally in night and day and unnaturally in a hospital room, serves to regulate our circadian rhythms and in turn, our sleep schedules, hormone levels, and bodily temperature.

Humans are dependent on light especially as it helps to moderate our circadian rhythms, a biological clock of sorts upon which many processes in our lives are based. An approximately 24-hour long cycle, it exists in humans as well as plants and animals cyclical sleeping and feeding patterns. Controlled by the suprachiasmatic nucleus in the hypothalamus, our circadian rhythm, as well as environmental factors, dictates the rise and fall of hormones, sleep cycles, and body temperature. Light, especially, regulates this cycle as informational markers of day and night enter the eye and are relayed to this center where photosensitive retinal ganglion cells regulate this rhythm. Manipulating the body’s exposure to light directly affects these cycles.

The circadian rhythm is a 24-hour cycle based on light exposure that causes melatonin levels in the body to fluctuate. Melatonin is secreted by the pineal gland and rises and falls as the body decreases exposure and increases exposure to natural light, respectively. A study conducted in Antarctica showed the direct effect of natural light. The study observed the rhythm of melatonin following a night shift at work. This readaptation was observed as more rapid in the summer when the exposure to natural sunlight is greater, than the winter. The presence of bright light assisted the readaptation of the melatonin rhythm. It is melatonin’s soporific effect that makes it such an integral part of all processes related to sleep and the sleep cycle as well as treatment specifically targeting sleep related illnesses. Manipulations of the levels of melatonin in the body can aid in inducing sleep at specific desired times in an attempt to readjust circadian rhythms or when sleep drive is insufficient.

The body’s desire for and dependency on natural light is seen in recognized disorders such as Seasonal Affective Disorder (SAD). This major depressive disorder that often presents with depression, decreased mood and motivation, irregular sleep patterns, and issues with metabolism and weight gain. Over the course of the year, the composition and wavelength of the light we perceive changes. The photoreception system the body uses to receive light is highly sensitive to blue light, of which there is less during the winter. This study observed that exposure to blue light activated associations of emotional stimuli in the hypothalamus and amygdala. The lack of blue light, and by extension the lack of stimulation in these parts of the brain during the winter when there is less exposure to blue light, is manifested in the depression and mood swings that accompany SAD.

Patients undergoing cancer treatment are susceptible to a variety of symptoms, one of the most common of which is cancer-related fatigue (CRF). “A distressing, persistent, subjective sense of physical, emotional, and cognitive tiredness or exhaustion related to cancer or cancer treatment that is not proportional to recent activity”3, CRF is often unresponsive to pharmacological treatments and, as a result, researchers at Mount Sinai Hospital in New York, NY have been experimenting with the potential effect of bright white light treatment on cancer patients with CRF. The circadian rhythm is greatly disrupted in patients with cancer and the lack of exposure to sunlight and bright white light due to constant hospitalization furthers this desynchrony. This study observed patients three years post chemotherapy or radiation for breast cancer under bright white light treatment or dim red light (DRL) treatment for their cancer-related fatigue. After four weeks 55% of patients receiving DRL treatment still experienced fatigue whereas no patient receiving BWL experienced fatigue. This study postulated that the BWL which most closely mimics a spectrum of sunlight had a stronger effect on the circadian rhythm of cancer patients. The biological clock we all have is less sensitive to DRL and as such was less affected by it as a means of treatment for CRF. These means of light therapy overall, both acted as valid treatments of cancer related fatigue.

Fifty years ago, treatment of disorders in this manner, relying heavily on exposure to light or art or music would have been written off as a waste of time. Patients could have expected purely physical treatments and would have experienced little to no regard for their mental health. This is not just an evolution of treatment, but a maturation of understanding what it means to be sick and that treatment cures beyond physical pain and illness. As a result of studies like these, what it means to be a doctor and care for someone’s health is also changing and moving forward.

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