Spending too much time indoors may affect your body in ways you don’t realize
Your body can tell the difference between a bright day outside and a day spent under office lights—even when you can’t.
Modern life has moved overwhelmingly indoors. We work inside, eat inside, exercise inside and often relax at night by staring at brightly lit screens. But humans evolved with a dramatically different pattern: bright light during the day and darkness at night.
Scientists are increasingly interested in what that mismatch may mean for sleep, alertness, mood and the internal clock that helps regulate much of our physiology.
Your brain uses light to tell time
Light doesn’t simply help you see. Specialized cells in the retina detect light and send information to the brain’s master circadian clock, helping the body determine when it should be awake and when it should prepare for sleep.
Daytime light is one of the strongest environmental signals your brain receives for keeping your internal clock synchronized with the 24-hour day.
An international group of researchers who developed recommendations for healthy daily light exposure concluded that people should generally get substantially brighter light during the daytime while reducing light exposure in the evening and keeping the sleeping environment as dark as possible.
The problem is that indoor lighting can be dramatically dimmer than daylight outside. A room that seems perfectly bright to us may still provide a relatively weak signal to the circadian system.
More outdoor light has been linked to better sleep
One particularly large study examined data from more than 400,000 UK Biobank participants and found that greater daytime outdoor light exposure was associated with several favorable outcomes, including easier waking, less tiredness and fewer insomnia symptoms.
The study also found associations between greater daytime light exposure and mood-related outcomes.
There is an important caveat. Much of this research is observational. People who spend more time outdoors may also exercise more, socialize more or differ in other ways from people who remain indoors.
Researchers can identify an association between daytime light and better sleep or mood without proving that simply going outside caused the improvement.
Still, the biological mechanism connecting light and circadian rhythms is well established, making daytime light exposure considerably more than a lifestyle fad.
You may be interested in reading: How Sleep Reboots Your Brain—And What Happens When You Skip It
Your internal clock does much more than control sleep
Circadian rhythms help coordinate changes throughout the body across approximately 24 hours. Sleep and wakefulness are the obvious examples, but body temperature, hormone release, metabolism and other physiological processes also follow daily patterns.
Research reviewed by the National Heart, Lung, and Blood Institute has explored how mistimed light exposure can disrupt this system.
The issue isn’t simply getting “enough light.” Your body responds differently depending on when that light arrives.
Bright light early in the day generally helps reinforce daytime alertness and synchronize the circadian clock. Bright light late at night can send the opposite message, potentially delaying the body’s preparation for sleep.
That creates one of the peculiar contradictions of modern life: many people spend their days in relatively dim indoor environments and their evenings surrounded by electric lights, televisions, tablets and phones.
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From the perspective of the circadian system, we’ve made our days darker and our nights brighter.
You may want to read: IBS and Shift Work: How to Support Your Gut Despite an Irregular Routine
Going outside offers something most rooms can’t
Opening the blinds is worthwhile, and sitting near a window can increase daytime light exposure. But outdoor daylight generally reaches intensities that are difficult to reproduce with ordinary residential or office lighting.
That doesn’t mean you need to spend hours hiking through the woods.
Even building more outdoor time into an ordinary day may substantially increase the amount of bright daytime light reaching your eyes.
Morning coffee on the porch, walking the dog, eating lunch outdoors or taking a short afternoon walk can all change the light environment you’re exposed to.
And there’s no requirement that you stare toward the sun—in fact, you shouldn’t. Ordinary outdoor exposure provides plenty of light.
Don’t confuse the light effect with the “nature effect”
There is also research linking green spaces and time in nature with various measures of well-being. That’s interesting, but it’s a somewhat different question.
When scientists study outdoor light, they are examining a specific biological signal received through the eyes. You can therefore receive an important dose of daylight while walking down a city sidewalk, sitting on a patio or standing in your driveway.
You don’t necessarily need wilderness to give your circadian system the contrast between day and night that it expects.
That distinction matters because it makes the idea practical for people who don’t live near parks or have the ability to spend long periods outdoors.
Final word
We have engineered an indoor world that’s comfortable enough to make us forget how dramatically different it is from the environment in which human biology developed.
That doesn’t mean indoor life is inherently unhealthy, nor does current research prove that a specific number of minutes outside will prevent disease. But the evidence that light regulates human circadian biology is strong, and observational research increasingly suggests that greater daytime light exposure is associated with better sleep, alertness and mood.
The practical lesson is remarkably simple: bright days and dark nights appear to be signals the human body still expects.
You don’t have to overhaul your life to provide them. Going outside in the morning, taking a daylight walk, opening the blinds during the day and dimming your environment as bedtime approaches may help restore some of the contrast modern life has erased.
