Ever fallen asleep with the lights on or scrolled through your phone right before bed? You’re not alone. But did you know that something as simple as room lighting at night could be silently sabotaging your health?
We’ve all heard the usual advice—“Turn off the lights before bed,” “Avoid screens at night”—but there’s more science behind it than just helping you fall asleep faster. Recent research shows that sleeping with lights on can mess with your blood sugar levels and your heart health—even after just one night.
What the Science Says
A study published in 2022 in the Proceedings of the National Academy of Sciences sheds light (pun intended) on this issue. The researchers wanted to understand how light exposure during sleep affects glucose (blood sugar) regulation. In other words, can a simple thing like having the bedroom light on make it harder for your body to handle sugar the next morning?
Turns out, the answer is yes.
The study involved 20 healthy young adults divided into two groups. One group slept in dim light for two nights. The other group spent the first night in dim light, and the second in brighter room lighting—equivalent to a softly lit room, not a spotlight.
The next morning, the researchers measured their blood sugar and other vital signs. Those who slept under brighter lighting showed signs of increased insulin resistance, which means their bodies weren’t using insulin as effectively to manage sugar in the blood. This is a red flag, because insulin resistance is linked to prediabetes, type 2 diabetes, and other metabolic issues.
Why Is Light at Night a Problem?
So how exactly does a light bulb disrupt your metabolism?
It comes down to your nervous system, sleep quality, and melatonin—the hormone that helps regulate your sleep-wake cycle.
Here’s what the researchers observed in people who slept with the lights on:
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Poorer sleep quality: Less time in deep and REM (rapid eye movement) sleep.
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Increased heart rate: A sign that the body wasn’t fully relaxed.
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Higher nervous system activity: Especially the sympathetic nervous system (the “fight or flight” system), which should be low during restful sleep.
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Lower melatonin levels: Light suppresses melatonin, which not only controls sleep but is also connected to insulin sensitivity and metabolism.
In simple terms, sleeping with the lights on keeps your body in a state of alertness—even while you’re asleep. And that internal stress can lead to poor blood sugar control.
Why It Matters
The takeaway from this research is important: even one night of light exposure while sleeping can negatively affect your metabolic health. Over time, if this becomes a regular habit, it could contribute to long-term issues like:
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Type 2 diabetes
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Heart disease
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Poor sleep quality
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Weight gain
And you don’t need to be glued to your phone for this to happen. A bedside lamp, hallway light, or TV glow is enough to disrupt your natural sleep and metabolic processes.
How to Improve Your Sleep—and Your Health
Luckily, there are simple steps you can take to improve your sleep hygiene and protect your long-term health. Here’s what experts suggest:
1. Stick to a Sleep Schedule
Try to go to bed and wake up at the same time every day—even on weekends. This helps regulate your internal body clock, making it easier to fall asleep and wake up naturally.
2. Create a Relaxing Bedtime Routine
Avoid screens (phones, tablets, TVs) at least an hour before bed. The blue light from these devices can block melatonin production. Instead, unwind with reading, journaling, or meditation.
3. Make Your Room Sleep-Friendly
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Keep it dark: Use blackout curtains or a sleep mask if needed.
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Stay cool: A cooler room temperature (around 65°F or 18°C) is ideal for most people.
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Minimize noise: Use earplugs or white noise if outside sounds keep you up.
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Ditch night lights: If you need one, use a red or amber night light, as these colors are less disruptive to melatonin.
4. Be Smart About Light
Try to limit artificial lighting in the evening. Dim the lights an hour before bed to help signal to your brain that it’s time to wind down.
If you use your phone or computer at night, turn on “night mode” or use blue light blocking glasses.
5. Invest in Comfort
A good mattress and pillow can significantly improve your sleep posture and depth of sleep. Your bed should support your body without causing aches or stiffness.
The Bottom Line
This study is a powerful reminder that even small changes in our environment—like lighting—can have a big impact on our health. The light that seems harmless at night might be working against your body while you sleep, disrupting your hormones, your rest, and even your blood sugar levels.
So the next time you think about falling asleep with the TV on or skipping your wind-down routine, think again. Dim the lights, put away your phone, and give your body the restful, healing sleep it needs.
After all, good sleep isn’t just about feeling rested—it’s about staying healthy, now and in the long run.
