#circadianrhythms — Public Fediverse posts

DATE: August 19, 2026 at 04:00PM
SOURCE: PSYPOST.ORG

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TITLE: Morning sunlight exposure is linked to earlier sleep schedules

URL: https://www.psypost.org/morning-sunlight-exposure-is-linked-to-earlier-sleep-schedules/

Exposure to natural sunlight early in the day is associated with earlier sleep schedules and better overall rest. Researchers found that adults who spent more time in the morning sun had a more aligned internal biological clock, which can promote healthier sleep patterns. The study was published in the journal BMC Public Health.

The human body relies on an internal biological clock, known as the circadian rhythm, to manage sleep and wake cycles. This rhythm is governed by a tiny region in the brain called the suprachiasmatic nucleus. When light enters the eyes, signals travel to this brain region, which then guides the release of various chemical messengers.

One major messenger is melatonin, a hormone that promotes sleepiness. When darkness falls, the body produces more melatonin. When the eyes detect bright light, melatonin production drops, promoting wakefulness.

Modern lifestyles limit how much natural light people receive. Many adults work indoors or spend their leisure time looking at screens. During the COVID-19 pandemic, lockdowns and remote work dramatically reduced the amount of time people spent outside.

Extended periods spent indoors can disrupt the biological clock. When a person’s biological time falls out of sync with their daily obligations, such as waking up early for work despite not feeling rested, they can experience chronic exhaustion. This misalignment is sometimes called social jetlag.

Lead researcher Luiz Antônio Alves de Menezes-Júnior, a public health and nutrition researcher at the Federal University of Ouro Preto in Brazil, and his colleagues wanted to understand how sunlight at different times of the day affects specific elements of sleep. The researchers focused heavily on a metric called the midpoint of sleep, which is the exact halfway mark between the time a person falls asleep and the time they wake up. An earlier midpoint indicates a sleep cycle that is well-synchronized with the natural progression of day and night. A delayed midpoint can mean the internal clock is out of sync with typical social and work schedules.

The researchers conducted a cross-sectional survey of 1,762 adults living in the Iron Quadrilateral region of Brazil between October and December 2020. Interviewers visited homes in two mid-sized cities, using protective measures to prevent the spread of the coronavirus. They randomly selected households from census data, aiming to capture a representative sample across various socioeconomic groups. The participants answered detailed questions about their general health, socioeconomic status, and daily habits.

To evaluate sleep, the participants completed the Pittsburgh Sleep Quality Index, which is a validated questionnaire used to measure different dimensions of rest over the previous month. This tool helped the researchers calculate each person’s total sleep time, the amount of time it took them to fall asleep, and their sleep efficiency. Sleep efficiency is the percentage of time a person spends actually sleeping while in bed. The questionnaire also provided the data needed to calculate each participant’s midpoint of sleep and their overall sleep quality score.

Overall, the participants reported an average total sleep time of just over seven hours per night. The average sleep midpoint was around 5:18 a.m., meaning the typical participant fell asleep shortly before midnight and woke up just after 7:00 a.m.

To track light exposure, the researchers asked the participants to estimate how many days a week they spent time in the sun. The participants then estimated how many minutes they spent in the sun on those days across three specific time windows. These windows were before 10 a.m., between 10 a.m. and 3 p.m., and after 3 p.m.

The research team used statistical models to look for relationships between the timing of sunlight exposure and the various sleep metrics. To analyze the results, they used a directed acyclic graph, which is a theoretical model that maps out how different variables might influence one another. This helped them select the correct factors to adjust for in their models, avoiding false associations. They factored in variables such as age, gender, education level, chronic health conditions, and levels of physical activity.

The researchers found that morning sunlight exposure had the strongest relationship with the midpoint of sleep. For every additional 30 minutes a participant spent in the sun before 10 a.m., their sleep midpoint shifted earlier by an average of 23 minutes. The findings suggest that morning light serves as a primary signal to help reset the biological clock.

Afternoon sunlight exposure also showed a relationship with the sleep midpoint, though the effect was smaller. Every 30 minutes of sun exposure after 3 p.m. was associated with a 19-minute earlier sleep midpoint. The researchers noted that afternoon sunlight might signal the approaching evening, or it might coincide with outdoor physical activity that generally aids sleep.

Sunlight exposure in the middle of the day, between 10 a.m. and 3 p.m., had no statistically significant association with the midpoint of sleep. The lack of an association between midday light and sleep timing suggests that the biological clock is most responsive to light at the extremes of the day.

Beyond the sleep midpoint, morning sunlight was the only time window associated with a better overall sleep quality score on the questionnaire. People who spent more time outside before 10 a.m. reported generally better rest.

Conversely, sunlight exposure at any time of day showed no statistically significant association with total sleep time. Light exposure also had no statistically significant association with how quickly participants fell asleep or their sleep efficiency.

The study relies on observational data, meaning it can only identify patterns rather than prove that sunlight exposure directly causes sleep changes. The participants estimated their own sun exposure and sleep habits, which can introduce memory errors or biases compared to using objective tracking devices.

The researchers calculated a single average sleep midpoint for each participant for the entire week. They did not separate sleep data for workdays versus weekends. People often sleep in on their days off to catch up on rest. A broader weekly average might mask the specific effects of varying daily schedules and weekend sleep habits.

The analysis did not track exposure to artificial light or the amount of time participants spent looking at screens in the evening. Late-day screen light is known to influence sleep onset and biological rhythms, which could skew the interpreted effects of natural sunlight. Additionally, the sleep efficiency data was based entirely on self-reports. Measuring true sleep efficiency generally requires clinical tools like movement-tracking wristbands or formal sleep studies in a laboratory setting.

The data collection took place during the first year of the COVID-19 pandemic, a period marked by high social isolation, anxiety, and altered work routines. These unique societal conditions likely influenced the participants’ stress levels and sleep patterns in ways that are difficult to separate from their light exposure. Future research could use wearable technology to measure outdoor light exposure and sleep patterns precisely, helping clarify exactly how natural light guides the human biological clock under normal daily conditions.

The study, “The role of sunlight in sleep regulation: analysis of morning, evening and late exposure,” was authored by Luiz Antônio Alves de Menezes-Júnior, Thais da Silva Sabião, Júlia Cristina Cardoso Carraro, George Luiz Lins Machado-Coelho, and Adriana Lúcia Meireles.

URL: https://www.psypost.org/morning-sunlight-exposure-is-linked-to-earlier-sleep-schedules/

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#psychology #counseling #socialwork #psychotherapy @psychotherapist @psychotherapists @psychology @socialpsych @socialwork @psychiatry #mentalhealth #psychiatry #healthcare #depression #psychotherapist #MorningSunlight #CircadianRhythms #SleepHealth #EarlyWakeTime #SunlightAndSleep #BiologicalClock #SleepQuality #MorningExposure #NaturalLightBenefits #SleepMidpoint

Why #LightPollution is a solvable #environmental crisis

Excessive #OutdoorLighting is deadly to #animals and takes a toll on #HumanHealth and wellbeing, too. But when it comes to large-scale environmental problems, this one may be a relatively easy fix.

By Alissa Greenberg
Friday, April 1, 2022

"In recent decades, lightbulbs made with #LEDs arrived, a revolution in energy efficiency with seemingly little downside. After all, an #LED bulb converts some 90% of the electricity it uses into light, whereas a conventional incandescent bulb only converts about 10%. And LED bulbs are touted as lasting up to 25 times longer.

"But the physics of LEDs make them fundamentally different from incandescents. While those traditional bulbs put out warm white light made of all colors mixed together, LEDs filter blue-rich light through a specialized phosphor material, producing light that appears white to the human eye but is still more blue-intense than incandescents’ light.

"But #BlueLight is also the most disruptive to our #nighttime environment because it mimics daylight, disrupting the hormone production and sleep cycles of both animals and humans.

"#Melatonin, one of those hormones, helps the immune system destroy renegade cells dividing out of control. That can lead to other health issues, including heightened rates of #cancer. And, 'we’re not the only ones who produce melatonin,' says Mario Motta, a cardiologist and trustee of the American Medical Association. Even amoebae produce melatonin'—meaning even amoebae might be vulnerable to light at night.

"The impacts of light pollution are evident everywhere from human health to astronomy research, but they come into particular focus in the recent phenomenon of global species #dieoffs. Between 100 million and a billion birds die every year due to light pollution, according to Massachusetts IDA chapter president James Lowenthal. New York City recently dealt with a huge die-off, 'with flocks of #MigratoryBirds slamming into buildings,' says Sarah Bois, an ecologist at the island’s Linda Loring Nature Foundation and a member of Nantucket Lights. 'They’re attracted to light.' A 2015 study at New York’s 9/11 'Tribute in Light'' installation showed an increase from 500 birds within half a kilometer of the light beams before they were turned on to 15,700 just minutes after.

"The issue is a double whammy for birds because they rely on #insects for food—and those populations are plummeting, with light pollution contributing significantly to the so-called "#InsectApocalypse.” By some estimates, one third of insects attracted to light sources at night die before morning, either due to exhaustion or because they get eaten. And according to a study in Germany, the number of insects in that country alone that die after being attracted to lights can number 100 billion or more in a single summer.

"Some starve to death searching for food that should appear bluer at twilight but is lit up amber under streetlights, says insect conservationist Avalon Owens, a doctoral candidate at Tufts University. Some are thrown off by light just the way we are, because of their #CircadianRhythms. #Pollinators whose schedules are altered by artificial light miss the #flowers they’re evolutionarily paired with, if the flowers naturally close and open with the warmth of the sun. And insects that rely on circadian rhythms for their yearly development don’t hibernate in time for winter and freeze to death.

"On #Nantucket, these phenomena are of particular concern because the island is home to a remarkably healthy population of northern long-eared #bats, which are endangered. Like many birds, the bats rely on insects for food and are easily dazzled by light, putting them in increasing jeopardy. Jack Dubinsky, director of the Maria Mitchell Aquarium on Nantucket, says he’s concerned that adding increasingly lit-up nights to the challenges of #ClimateChange, water quality, and #ecosystem collapse could put huge pressure on some already struggling species. 'The more curveballs we throw, the less likely they’ll be able to find their way,' he says.

Read more:
https://www.pbs.org/wgbh/nova/article/light-pollution-led-nantucket-solutions/

#DarkSkies #Extinction #StreetLights