Exposure to sunlight may be the key to better sleep: Research shows offices workers without windows sleep worse

Many people think improving insomnia relies only on relaxing before bed or going to sleep earlier. However, family medicine physician Dr. Chan Yan-mei cites research showing that daytime light exposure is actually the key to regulating sleep. If people chronically lack natural light, their circadian rhythms can easily become disrupted, making it difficult to sleep well even if they go to bed early. Research shows that camping and moderate sun exposure help adjust sleep cycles – a simple, free sleep aid.

The Day-Night Hormonal Handover Mechanism

Chan explains that while most people think of melatonin for sleep, there is also cortisol, commonly known as the "stress hormone." She describes cortisol as the body's "day-shift doctor." It surges to its daily peak 30-45 minutes after waking, then slowly declines throughout the day, reaching its lowest point late at night. Melatonin is the opposite – the body's "night-shift doctor." It stays very low during the day, starts rising around 9 PM, and peaks between 2-4 AM.

Chan states that when this day-night hormonal handover goes smoothly, the body naturally produces sleepiness. If this rhythm is disrupted, you may toss and turn even when it's time to sleep. Therefore, insomnia is often not just a nighttime problem but the result of a full-day circadian rhythm imbalance.

Office Workers with Windows Have Better Sleep Quality

In modern lifestyles, many office workers spend all day indoors, assuming the bright environment is sufficient. However, indoor light levels differ vastly from outdoor natural light. Typical office lighting is about 300-500 lux – roughly 0.5% of a sunny day's 50,000-100,000 lux. Many people think they work in a "bright place," but their body's internal clock isn't receiving strong enough light signals.

Chan cites a 2014 study from the University of Illinois and Northwestern University published in the Journal of Clinical Sleep Medicine. The controlled study of 49 office workers showed that those in offices with windows had significantly longer sleep duration and better overall sleep quality, while the windowless group showed the opposite.

Chan explains that the body's circadian rhythm needs light to calibrate. If daytime light exposure is insufficient, the brain may not correctly distinguish day from night, affecting melatonin secretion and sleep quality.

A 30-Minute Walk Outdoors: Natural Light Regulates Sleep

So how can office workers improve their sleep? Chan further cites a 2013 study from the University of Colorado published in Current Biology. In this experiment, participants went mountain camping for one week, exposed only to natural daylight during the day and no artificial light at night. After just one week, participants' "desired sleep time" shifted a full 2 hours earlier. Someone who normally felt sleepy at 11 PM began yawning at 9 PM. In 2017, the research team followed up on a more practical question: most people can't take a week off to camp. They found that even camping only during weekends (Saturday and Sunday) achieved 69% of the effect of a full week of camping.

Chan notes that for office workers, this means avoiding sleeping in and scrolling on your phone on weekend mornings. Instead, stepping outside for a 30-minute walk can shift your entire week's "desired sleep time" earlier. You don't truly need to camp – a "mini version" of the method yields most of the benefits.

Many think improving insomnia requires medication or supplements, but morning light exposure has been proven to enhance sleep quality. Chan cites a 2016 systematic review from the University of Amsterdam. The review analyzed 53 studies with 1,154 participants and found that morning light therapy helps shorten the time to fall asleep and improves insomnia. The stronger the light intensity, the more pronounced the effect.

Additionally, a 2022 double-blind study from Inha University in Korea, published in Psychosomatic Medicine, experimented on 56 post-stroke insomnia patients. Using a 10,000 lux light therapy lamp for 30 minutes each morning for just 2 weeks significantly shortened their sleep onset latency and improved sleep efficiency.

Simple Anti-Insomnia Habit: Open the Curtains When You Wake Up

Chan also shares that she personally struggled with insomnia as a resident physician. Now, the first thing she does upon waking every day is open the curtains to let natural light in, helping her body quickly start up its circadian clock. She suggests that if you chronically have sleep problems, try starting with 10-30 minutes of morning sunlight. It might bring unexpected improvements to your sleep.

Chan reminds that many people habitually sleep in until noon on weekends to catch up on rest, but this can further disrupt the circadian rhythm. She points out that rather than blindly extending sleep time, it's better to maintain a regular schedule and increase daytime sunlight exposure. Ideally, receiving natural light exposure daily is the simplest and most practical way to adjust your sleep cycle.

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