Insufficient exposure to daylight and excessive exposure to light at night can disrupt circadian rhythms, leading to adverse health effects and an increased risk of death.
Given the impact of light on health, optimizing exposure is crucial.
Significance of Light Exposure
The study also explored the relationship between light exposure and death from cardiometabolic risk factors, which affect the heart, blood, and blood vessels, such as obesity, high blood pressure, unhealthy cholesterol levels, and elevated blood sugar levels.
Researchers analyzed data from light sensors worn for a week, totaling 13 million hours and representing around 89,000 participants. They compared this light data with death records from the National Health Service over an approximately eight-year period. Additionally, they estimated sleep duration and efficiency from motion data.
The results indicated that light exposure can either strengthen or disrupt circadian rhythms depending on the timing of exposure. Circadian rhythms are the natural fluctuations that occur in the body over a 24-hour period and influence various bodily functions like sleep, digestion, hormone release, and body temperature.
Participants with higher exposure to daylight had death rates that were 17–34 percent lower. The effects were dose-dependent, meaning the more light exposure, the lower the risk of death. Conversely, those with greater exposure to light at night had death rates that were 21–34 percent higher. Again, the risk increased with greater exposure. This heightened risk of death applied to all causes, including cardiometabolic diseases specifically. While “all-cause” mortality encompasses deaths from cardiometabolic diseases, it also includes deaths from other conditions like cancer and neurodegenerative diseases.
“Minimizing exposure to light at night, maximizing exposure to light during the day, and maintaining regular light-dark patterns that support circadian rhythms may enhance cardiometabolic health and longevity,” concluded the researchers in the study.
Impact of Disrupted Circadian Rhythms
The study underscored that circadian rhythms play a crucial role in how light exposure affects health. These rhythms are regulated by circadian clock genes, with a brain structure known as the master clock coordinating their functions. When disruptions occur, such as exposure to light before bedtime, circadian rhythms can be thrown off balance, increasing the risk of health issues.
The researchers noted that previous studies have linked disrupted circadian rhythms to the development of conditions like obesity, diabetes, and metabolic syndrome—a group of conditions that heighten the risk of heart disease and diabetes.
Conversely, strengthened circadian rhythms may explain the association between higher light exposure during the day and a reduced risk of death. Strengthening circadian rhythms could also offer protection against the negative effects of disrupted rhythms.
The researchers also found that while previous studies have linked an increased risk of death to sleep disturbances, the effects of night light exposure on circadian rhythms can predict the risk of death independently of sleep quality.
Supporting Evidence
Previous studies focusing on night owls and shift workers provide additional support for the findings of this study.
Night Owls
A cohort study published in Chronobiology International examined the connection between death risk and individuals with a preference for later sleep schedules, commonly known as night owls. The study analyzed data from the UK Biobank on 433,268 adults aged 38–73, with follow-up averaging 6.5 years. Results indicated that night owls had a higher risk of death from all causes, possibly due to the effects on circadian rhythms.
Shift Workers
A cohort study published in the American Journal of Preventive Medicine assessed the impact of shift work on mortality. The study involved 74,862 registered nurses from the Nurses’ Health Study. Compared to women who never worked night shifts, those with five or more years of rotating shift work had a slight increase in death risk from heart disease and all causes. Women with at least 15 years of rotating shift work saw a modest rise in death risk from lung cancer. The U.S. Centers for Disease Control and Prevention have noted that shift work can disrupt circadian rhythms.
Tips for Light Exposure
Bjørn Ekeberg, co-founder and CEO of Recharge Health and creator of FlexBeam, shared light exposure tips with The Epoch Times via email.
- Get 15–30 minutes of sunlight exposure early in the day to enhance overall health and support circadian rhythms.
- If adequate sunlight exposure is not feasible, consider a 10-minute session of red-light therapy during the day. Red-light therapy, involving exposure to red and near-infrared light, can be beneficial when done early as it lacks blue light wavelengths that disrupt sleep.
- In the evening, reduce exposure to artificial sources of light, especially 1–2 hours before bedtime. Blue light from screens like TVs, computers, and phones can stimulate the brain and hinder melatonin production, affecting sleep.
- Avoid overhead LED lights in the evening as they emit unnatural wavelengths that can disturb circadian rhythms.
- To prepare for bedtime, dim direct light sources, such as screens and lamps, and opt for warm-tone lighting over bright ceiling lights.
Natural vs. Artificial Light
Ekeberg emphasized the importance of sunlight, stating that humans require the sun’s energy just like plants do. Sunlight not only provides direct energy that the body can convert through skin exposure but also plays a vital role in regulating circadian rhythms and sleep-wake cycles.
According to Ekeberg, sunlight encompasses a full spectrum of electromagnetic energy, from ultraviolet rays to visible light wavelengths like blue, green, and red, all the way to infrared wavelengths. Exposure to sunlight ensures a comprehensive range of beneficial light wavelengths, particularly red and near-infrared.
In contrast, indoor lighting, particularly LED lights, typically consists of visible light only, with high levels of blue light that can disrupt circadian rhythms when used at night. While indoor lighting enables visibility, it does not replicate the health benefits of natural sunlight. Excessive exposure to indoor lighting can even have detrimental effects on health.
