The circadian rhythm, also known as the “biological clock”, is strongly influenced by external light. Normally, various functions within the body are maintained by adjusting this clock through a bright day and dark night environment; However, if we are exposed to bright light at night or spend long hours in a dark environment during the day, our circadian rhythms are disrupted. A new study published in the journal Proceedings of the National Academy of Sciences of the United States of America (PNAS) found that constant exposure to light is associated with an increased risk of premature death.
“Disruptions in circadian rhythms have been shown to cause a variety of health problems, including diabetes, obesity, cardiovascular and mental illness, as well as an increased risk of death,” says Sean W. Cain, sleep expert and author of study from Flinders University, in Australia.
What does the study indicate?
Cain and his colleagues studied approximately 89,000 people aged 40 to 69 registered with the UK Biobank, a research organization that tracks the effects of genetic predisposition and living environment on long-term diseases. The patients wore a light sensor on their wrist, so the team was able to record exposure day and night daily for eight years. After extensive monitoring, found that people exposed to bright light at night had a 21% to 34% increased risk of death. In contrast, those who received sufficient light exposure during the day had between 17 and 34% lower risk of death.
Specialists detail that exposure to bright light at night throws off the signals that control circadian rhythms throughout the body. This suppresses the amplitude of the signal and disrupts the biological clock. On the other hand, exposure to bright light during the day reduces the body’s sensitivity to light at night. As a result, the rhythm is stabilized and health hazards are reduced.
Negative effects of alteration of the biological clock
They also examined mortality risk by analyzing the phase and amplitude of the circadian rhythm, based on information about the light to which the subjects were exposed. The study confirms that the risk of premature death increases in people whose rhythm amplitude is small, or whose phase is extremely advanced or delayed, that is, those patients with a large discrepancy between real time and their biological clock. They also ruled that these organisms appeared to have a high risk of death from cardiovascular disease and metabolic disorders. The negative effects of exposure to bright light at night had already been proven in animal experiments: When the biological clock is altered, the suprachiasmatic nucleus, which is the central part of the brain, is affected, the same happens with hormonal secretion, the regulation of body temperature, blood pressure, etc. This can cause metabolic problems such as increased blood sugar and reduced insulin sensitivity.
The study results suggest that improving the light environment in daily life may be an effective means of prolonging healthy lifespan. To maintain good long-term health, Cain’s team recommends exposure to bright light during the day and staying in dark environments at night.
Article originally published in WIRED Japan. Adapted by Alondra Flores.
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