Since ancient times, humans have followed the rhythm of working during the day and resting at night. With the invention and popularization of electric lights, this pattern has gradually been broken; night is no longer pitch black but illuminated by various light sources.

However, this change is not without cost. Recently, a study published in the renowned academic journal Nature revealed a startling fact: incorrect lighting, especially excessively strong light at night, may be the "original sin" that accelerates aging and triggers diseases. This finding has attracted widespread attention, and it has led people to reconsider the potential impact of nightlights and other nighttime light sources on health.

Increased risk of heart disease:This study, which included nearly 90,000 middle-aged and elderly people aged 55-70, found a significant association between nighttime light intensity and the risk of heart disease. Compared with respondents in the 0% to 50% nighttime light intensity range, the risk of death from heart disease increased by 20% to 26% in the 70% to 90% range, and by 33% to 46% in the brightest 90% to 100% range.

Trigger other age-related diseases:In addition to cardiovascular diseases, excessively strong light at night may increase the incidence of a series of age-related diseases by 13% to 30%, including obesity, cancer (such as breast cancer), mental illness, sleep disorders, hypertension, and diabetes.

In stark contrast to the dangers of nighttime light exposure, bright daytime light has many benefits for human health. Studies have found that daytime light can reduce the risk of death and disease. Specifically, brighter daytime light can offset 9% to 39% of the increased mortality risk due to excessive nighttime light. This shows that appropriate daytime light is crucial for maintaining human health.

After in-depth research, scientists published their research findings in the top biological journal Nature, revealing the physiological basis of light's impact on health.

They found that the intrinsically photosensitive retinal ganglion cells (ipRGCs) in the eyes play a key role in light perception. These cells can convert light energy into nerve signals and transmit them to key areas such as the suprachiasmatic nucleus, the paraventricular nucleus, and the preoptic area of the hypothalamus, affecting the secretion of melatonin (sleep-related) and corticotropin-releasing hormone (stress-related), thereby regulating physiological processes such as sleep, metabolism, body temperature, and mood. When external light is disrupted, these physiological processes will also be affected, leading to a series of health problems.

Various neural activities and physiological processes regulated by light

In addition, the study also found that even with eyes closed, light can penetrate the scalp and skull to directly activate deep brain tissue. At the same time, there are substances in the human peripheral tissues and organs that can "see" light—non-visual photoproteins. When these substances sense light, they can play a role in regulating vasodilation, lipolysis, heat production, and energy consumption. These findings further reveal the complex mechanisms of light's impact on human health.

Nighttime light sources may bring us convenience and a sense of security, but they may also be "invisible killers" that accelerate aging and trigger diseases. Therefore, we should pay more attention to the impact of light on health, reasonably arrange our work and rest time, and choose suitable light sources and lighting methods. Only in this way can we maintain a healthy body and a pleasant mood while enjoying the convenience brought by technology.

References:

[1] D.P. Windred, A.C. Burns, Brighter nights and darker days predict higher mortality risk: A prospective analysis of personal light exposure in >88,000 individuals, Proc. Natl. Acad. Sci. U.S.A.121 (43) e2405924121,DOI: 10.1073/pnas.2405924121.

[2] Rao, F., Xue, T. Circadian-independent light regulation of mammalian metabolism. Nat Metab 6, 1000–1007 (2024). DOI: 10.1038/s42255-024-01051-6.