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We often think of a good night’s sleep in terms of duration—the coveted seven to nine hours. While getting enough sleep is crucial, a growing body of research is illuminating another critical factor: the darkness, or lack thereof, in our sleep environment.

For many of us, falling short on sleep is a common reality. In fact, more than one-third of American adults report not getting enough sleep on a regular basis [1]. But beyond just feeling tired, the quality of our sleep environment itself could be sending subtle stress signals to our bodies, even while we are unconscious.

Emerging science suggests that even a small amount of light in your bedroom at night—from a stray streetlight, a television, or a glowing alarm clock—may have measurable effects on your cardiovascular and metabolic health.

What the Research Shows

A compelling 2022 study published in JAMA Internal Medicine explored the connection between light exposure during sleep and health risks. In this observational study involving older adults, researchers found that any light exposure during sleep was associated with a higher prevalence of obesity, high blood pressure, and diabetes compared to sleeping in a room with no light [2]. While this type of study shows a strong association, it does not prove direct causation.

The proposed mechanism centers on our body’s master internal clock, the circadian rhythm. This 24-hour cycle governs nearly all of our physiological processes, including sleep-wake patterns, hormone release, and metabolism [3]. Light is the single most powerful environmental cue for synchronizing this internal clock.

When light enters our eyes, it signals to a part of our brain that it is daytime. This process suppresses the release of melatonin, a key hormone that tells the body it’s time to sleep [4]. Exposure to light at night, therefore, can confuse our internal clock. The researchers in the JAMA study noted that sleeping with even moderate ambient light may result in an increased heart rate during the night and higher insulin resistance the following morning [2].

Insulin resistance is a condition where cells in your muscles, fat, and liver don’t respond well to insulin and can’t easily take up glucose from your blood. Over time, this can increase your risk for developing type 2 diabetes. The findings suggest that light at night may act as a form of physiological stress, activating the sympathetic nervous system (“fight-or-flight” response) when the body should be in a state of rest and repair [5].

What This Means for Everyday Wellness

This research doesn’t suggest we need to live in a cave, but it does highlight the power of creating a truly dark sleep sanctuary. It’s a simple, non-pharmacological way to support your body’s natural rhythms. Here are a few ways to apply this insight:

Audit Your Bedroom for Light: Take a moment tonight to stand in your bedroom with the lights off. Notice the small sources of light you may have overlooked—the power indicator on your TV, the glow from a phone charger, or the digital display on your alarm clock. Cover these with tape or turn them off if possible.

Embrace True Darkness: The most effective way to block external light is with blackout curtains or blinds. If that’s not an option, a comfortable sleep mask can create a personal pocket of darkness and is an excellent tool for travel as well.

Manage Your Evening Light Diet: The two to three hours before bed are crucial for priming your body for sleep. Dim the lights throughout your home. Avoid tablets, smartphones, and laptops, or use their built-in “night mode” settings to shift the screen color to warmer, less-disruptive tones [4].

Rethink the Nightlight: If you need a light for safety, opt for one that is very dim and uses a red or amber wavelength, as these are less disruptive to melatonin production than blue or white light [5]. Place it low to the ground so the light is not directly in your line of sight if you wake up.

A Gentle Reminder

Cultivating a better sleep environment is an act of deep self-care. Small, intentional changes to your nightly routine can help align your body with its natural, restorative rhythms, supporting your wellness from the inside out.

Sources and Resources

1. [1] CDC. 1 in 3 adults don’t get enough sleep (2022-05-18). https://www.cdc.gov/media/releases/2016/p0215-enough-sleep.html
2. [2] JAMA Network. Light Exposure During Sleep and Cardiometabolic Risk in Adults (2022-06-01). https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/2790159
3. [3] National Institute on Aging. Circadian Rhythms (2020-11-03). https://www.nia.nih.gov/health/circadian-rhythms
4. [4] Harvard Health Publishing. Blue light has a dark side (2020-07-07). https://www.health.harvard.edu/staying-healthy/blue-light-has-a-dark-side
5. [5] New England Journal of Medicine. Illuminating the Role of Light in Human Health (2022-07-28). https://www.nejm.org/doi/full/10.1056/NEJMra2201949

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Educational disclaimer: This article is for general wellness education only. It is not medical advice and does not diagnose, treat, cure, or prevent any condition. It is not a substitute for consultation with a qualified healthcare professional. Always speak with your clinician before starting or changing any medication, supplement, or wellness routine, especially if you are pregnant, nursing, taking medication, or managing a health condition.

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