Light is one of the most powerful cues that regulate the body’s circadian rhythm, the internal clock that governs when we feel awake and when we feel sleepy. While many people fall asleep with a lamp on, the television glowing in the background, or streetlights seeping in through the window, research suggests that too much light during sleep is far from harmless. Studies now indicate that sleeping in light-polluted environments may increase health risks ranging from poor sleep quality to metabolic and cardiovascular issues.
Exposure to light at night directly interferes with melatonin, the hormone that signals to the body it is time to rest. The Journal of Clinical Endocrinology & Metabolism reports that even low levels of light during sleep can suppress melatonin production, leading to shallower sleep cycles and frequent awakenings. Melatonin is not just critical for regulating sleep but also plays a role in immune function and protection against oxidative stress, meaning long-term disruption may affect more than just rest.
Research has also connected nighttime light exposure to metabolic and cardiovascular health. A study from Northwestern University published in PNAS found that participants exposed to moderate light during sleep had elevated heart rates and impaired glucose tolerance compared to those who slept in darkness. These changes are linked to an increased risk of diabetes and heart disease over time. The researchers noted that even brief exposure to indoor light during sleep could activate the sympathetic nervous system, the part of the body responsible for the “fight or flight” response, which should be at rest during nighttime hours.
In addition to physical health risks, light at night may contribute to weight gain and obesity. The American Journal of Epidemiology observed that individuals who regularly slept with a television or light on were more likely to experience long-term weight gain, possibly due to disrupted circadian regulation of metabolism and appetite hormones like leptin and ghrelin. This highlights how environmental light can extend its impact beyond sleep into broader aspects of health.
Blue light emitted from electronic devices poses a particular concern. Blue wavelengths are especially potent at delaying melatonin release, according to the National Institute of General Medical Sciences. Falling asleep near a smartphone, tablet, or television can trick the brain into perceiving it is still daytime, pushing back the body’s natural sleep-wake cycle and leading to less restorative rest.
The evidence is clear that minimizing light exposure during sleep can help protect both sleep quality and long-term health. Simple solutions such as blackout curtains, eye masks, dimming or turning off electronics, and avoiding bright screens before bedtime can create a healthier sleep environment. These steps not only support better rest but may also reduce the risk of developing chronic conditions associated with disrupted circadian rhythms.
Disclaimer: This article is for informational purposes only and does not provide medical advice. If you are experiencing persistent sleep disturbances or related health concerns, consult a healthcare professional for proper evaluation and treatment.
References:
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Cho, Y., Ryu, S. H., Lee, B. R., Kim, K. H., Lee, E., & Choi, J. (2015). Effects of artificial light at night on human health: A literature review of observational and experimental studies applied to exposure assessment. Chronobiology International, 32(9), 1294–1310.
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Obayashi, K., Saeki, K., & Kurumatani, N. (2014). Bedroom light exposure at night and the incidence of depressive symptoms: A longitudinal study. Journal of Clinical Endocrinology & Metabolism, 99(9), 3316–3321.
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Zhang, N., et al. (2022). Light exposure during sleep impairs cardiometabolic function. Proceedings of the National Academy of Sciences (PNAS), 119(12), e2113290119.
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Park, Y. M., White, A. J., Jackson, C. L., Weinberg, C. R., Sandler, D. P. (2019). Artificial light at night and obesity in a large U.S. cohort of women. American Journal of Epidemiology, 188(3), 569–577.
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National Institute of General Medical Sciences. (2020). Circadian rhythms fact sheet. Retrieved from https://www.nigms.nih.gov