A study published in the Proceedings of the National Academy of Sciences (PNAS) found that exposure to high levels of light at night can increase death risk by up to 34 percent. Conversely, exposure to high levels of light during the day can reduce death risk by up to 34 percent. The wrong timing and amount of light exposure disrupts circadian rhythms, which leads to heart disease, diabetes, mental health conditions, and obesity, thus increasing the risk of death.

“These new insights into the potential adverse impact of light have shown us just how important personal light exposure patterns are for your health,” senior author and sleep expert professor Sean Cain from Flinders University said in a statement.

Given how light affects health, it is beneficial to optimize exposure.

Light Exposure Matters

The study also investigated how exposure affects death from cardiometabolic risk factors, which include those affecting the heart, blood, and blood vessels, such as obesity, high blood pressure, unhealthy cholesterol, and high blood sugar.

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. They also 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.

Participants with brighter daylight exposure had 17 percent to 34 percent lower death rates. The effects were dose-dependent, with the greater the light exposure, the lower the death risk, according to the statement. Those with brighter night light exposure had 21 percent to 34 percent higher death rates—the greater the exposure, the higher the risk. Heightened death risk involved all causes, as well as cardiometabolic disease, specifically. While “all-cause” includes deaths from cardiometabolic disease, it also includes deaths from any other illness, such as cancer and neurodegenerative disease.

“Minimizing night light, maximizing day light, and keeping regular light–dark patterns that enhance circadian rhythms may promote cardiometabolic health and longevity,” the researchers in the study said.

Disrupted Circadian Rhythms

The study highlights that circadian rhythms are the primary factor underlying the effects of light exposure on health. The rhythms are set by circadian clock genes, and a brain structure called the master clock coordinates them to work together. When something happens to put a rhythm out of synch, such as light exposure before bedtime, it becomes disrupted, which increases the risk of poor health.

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.

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.

The researchers noted that earlier studies associate all-cause death risk with sleep issues. However, they determined that short sleep is only partially responsible for the higher death risk linked to night light exposure, as effects on circadian rhythm can predict death risk regardless of sleep quality.

Corroborating Evidence

Earlier studies involving night owls and shift workers provide some corroborating evidence for the study’s findings.

Night Owls

A cohort study published in Chronobiology International investigated the link between death risk and people with a later preference for sleep, known as evening types and commonly called night owls. (A cohort study follows a group of people over a period of time.)

The study analyzed UK Biobank data on 433,268 adults aged 38 to 73 and followed up for an average of 6.5 years. Results show that night owls had a higher risk of death from all causes. The researchers suggested that this may stem from the effects on circadian rhythms.

Shift Workers

A cohort study published in the American Journal of Preventive Medicine assessed the effects of shift work on death risk. It involved 74,862 registered nurses from the Nurses’ Health Study.

Compared with women who never worked night shifts, those with five or more years of rotating shift work had a modest increase in death risk from heart disease and all causes. Women who worked at least 15 years of rotating shift work had a modest increase in death risk from lung cancer. The Centers for Disease Control and Prevention has stated that shift work can disrupt circadian rhythms.

Light Exposure Tips

Bjorn Ekeberg, co-founder and CEO of Recharge Health, creator of FlexBeam and international speaker on the nature of light, provided tips to The Epoch Times in an email.

• Get 15 to 30 minutes of sunlight exposure early in the day to improve general health, as it helps set circadian rhythms.
• If getting enough sunlight exposure is not possible, a daytime 10-minute session of red-light therapy, which is exposure to red and near-infrared light, may help. It is best to do it early in the day because the sun is naturally richer in these wavelengths during this time. Red light therapy does not have any blue light wavelengths that disrupt sleep and can be safely used.
• Later in the evening, after dark, limit sources of artificial light. This is especially the case one to two hours before bedtime, as bluer light sources, such as screens from TVs, computers, and cellphones, can stimulate the eyes and the brain and prevent melatonin production before bed. Melatonin is a hormone that promotes sleep.
• Avoid exposure to overhead LED lights in the evening. These wavelengths are distorted and unnatural, and the body responds more strongly to light from above than below.
• To ease into bedtime mode, dim direct light sources in your eyes—such as screens and lamps—avoid ceiling floodlights and choose warm-tone lighting.

Outdoor Versus Indoor Light

“Everything in the world depends on sunlight,” Ekeberg said. “Humans need the energy from the sun as much as plants do.”

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.”