Brighter Nights and Darker Days May Lead to Early Death

Researchers analyzed 13 million hours of data—representing approximately 89,000 participants—from light sensors worn for one week. They compared the light data with death records from the National Health Service that occurred over approximately eight years. Additionally, they estimated sleep duration and sleep efficiency from motion data.
The results indicated that light either strengthens or disrupts circadian rhythms, depending on the time of exposure. Circadian rhythms are the changes a person experiences over 24 hours that influence many bodily functions, such as sleep patterns, digestion, hormone release, and temperature.
Researchers in the study noted that earlier studies associated circadian rhythm disruption with the development of obesity, diabetes, and metabolic syndrome—a cluster of abnormalities that increase the risk of heart disease and diabetes.
In contrast, strengthened circadian rhythms may underlie the link between brighter light exposure in the day and lower death risk. Strengthened circadian rhythms may also help provide protection from the harmful effects of disrupted circadian rhythms.
Sunlight provides a direct source of energy that the body can convert from skin exposure, he said. It also directly enhances circadian rhythm and helps regulate wake-sleep cycles.
According to Ekeberg, sunlight contains the full spectrum of electromagnetic energy, from ultraviolet rays through the visible spectrum of light—such as blue, green, and red—to infrared wavelengths. When we receive sunlight exposure, we get a complete range of light, including wavelengths shown to be particularly beneficial, which are red and near-infrared.
“In contrast, indoor lighting, and especially LED lights, are compressed for visible light only and are typically high in blue light wavelengths that can be disruptive to circadian rhythms when it’s dark outside,” Ekeberg said.
“Indoor lighting is made so we can see, but it is no replacement for natural sunlight. The sun brings health benefits while excessive indoor lighting can be detrimental to health.”