Before the invention of the electric light, people tended to go to bed when the sun went down and rise when the sun came up.

Nights were dark, and days were bright, a cycle conducive to sleep. This natural cycle, known as the circadian rhythm, is a 24-hour internal clock that regulates the sleep-wake cycle and other bodily functions.

Today, things are different. Light bombards every part of our lives at night, from lamps to computers, e-readers and mobile phones. Those devices emit blue light, considered an endocrine disrupter, that impacts the secretion of melatonin (the sleep hormone) and estrogens.

Then, we spend most of our daytime hours indoors, away from the warm, bright sunlight.

This hasn’t been good for our health…

Exposure to light at night can raise risks for breast cancer, obesity, type 2 diabetes and depression. It’s even been linked to high blood pressure and heart disease.

Now, there’s more bad news for those of us who experience brighter nights and darker days…

Light exposure and death risk

An international team of researchers conducted a study that revealed the crucial relationship of personal light exposure with all-cause and cardiometabolic mortality risk in 89,000 UK Biobank participants between the ages of 40 and 69. The following data was gathered:

• The participants wore light sensors on their wrists to measure exposure.
• Sleep duration and efficiency and midsleep were estimated from motion data.
• Mortality data was captured by the National Health Service across a follow-up period of about eight years. Cardiometabolic death was defined as any cause of death corresponding to diseases of the circulatory system or endocrine and metabolic diseases.

Results showed that light exposure makes a night and day difference in lifespan…

Those who were exposed to high levels of light at night had a 21 to 34 percent increased risk of death.

In comparison, those exposed to high levels of daylight had a 17 to 34 percent reduction in their death risk.

“Exposure to brighter nights and darker days can disrupt our circadian rhythms, a disruption that is known to lead to various health issues including diabetes, obesity, cardiovascular disease, mental health issues and increase the risk of death,” says senior author and sleep expert Sean Cain, a professor at Flinders University in Australia.

“These new insights into the potential adverse impact of light have shown us just how important personal light exposure patterns are for your health,” Cain adds.

According to co-senior author Andrew Phillips, a professor at Flinders, light exposure at night disrupts circadian rhythms by shifting the timing and weakening the signal of the body’s central “pacemaker,” which directs circadian rhythms throughout the body.

“Disruption to the body’s circadian rhythms is linked to the development of metabolic syndrome, diabetes and obesity and is also strongly implicated in the development of cardiometabolic diseases including myocardial infarction, stroke and hypertension,” Phillips says.

The study also demonstrated a disrupted circadian rhythm predicted a higher death risk.

“Our findings clearly show that avoiding night light and seeking daylight may promote optimal health and longevity, and this recommendation is easy, accessible and cost-effective,” Phillips says.

Keeping your circadian clock in sync

According to lead author Dr. Daniel Windred, these findings show the importance of enhancing our circadian rhythms by seeking bright light during the day and maintaining a dark environment across the late night and early morning hours, when the circadian “pacemaker” is most sensitive to light.

“Protection of lighting environments may be especially important in those at risk for both circadian disruption and mortality, such as in intensive care or aged-care settings,” Windred says.

“Across the general population, avoiding night light and seeking daylight may lead to reduction in disease burden, especially cardiometabolic diseases, and may increase longevity,” he adds.

Some tips for reducing your light exposure at night include:

• Invest in blackout curtains for the bedroom. This is especially necessary if you live in an urban environment where streetlights shine into your bedroom window.
• Turn off all light-emitting devices in the bedroom. This includes night lights and alarm clocks.
• Leave your electronics outside the bedroom. Don’t bring your e-reader, mobile phone or computer into the bedroom, especially right before you go to sleep. If you use your phone for your alarm, make sure the screen isn’t lit up when you go to bed.
• Use red-light night lights in the hallway and bathroom. These types of night lights don’t emit blue light, which keeps you awake. They also keep you from turning on bright overhead lights if you need to use the bathroom in the middle of the night.

As for daylight exposure, try to spend some time outdoors every day, especially in the winter when the days are short. If you’re too busy to get outside, make sure you’re at least spending time in a room with windows that let in plenty of natural sunlight.

Sources:

Brighter nights and darker days could lead to an early grave — ScienceDaily

Brighter nights and darker days predict higher mortality risk: A prospective analysis of personal light exposure in >88,000 individuals — PNAS