Is Light at Night Making Us Sick? A Global Study Links Artificial Light to Cancer Risk
Most of us take artificial lighting for granted. From bedroom lamps to glowing phones and city streetlights, we’re exposed to artificial light at night (ALAN) more than ever before.
But what if this modern convenience is quietly raising our cancer risk?
A large international study examined light pollution across 158 countries — and found a strong link between nighttime light exposure and several types of cancer, including breast, colorectal, lung, and prostate cancer.
Let’s break it down.
What the Study Looked At
Researchers used two global indicators to measure light pollution:
PALI (Protected Area Light Pollution Indicator): measures direct exposure to artificial light in natural protected areas
PAHI (Protected Area Human Influence Indicator): measures how much human activity and lighting surrounds those areas
They compared these indicators to cancer rates in 158 countries, while accounting for other factors like population size, electricity use, air pollution, and forest coverage.
What They Found
Both PALI and PAHI were positively associated with:
All cancers combined
Breast cancer
Lung cancer
Colorectal cancer
Prostate cancer
The association was strongest with PAHI — showing that even indirect human-made light exposure can have biological consequences.
After adjusting for other variables, PAHI alone explained up to 35.5% of the variation in colorectal cancer rates and 34.1% in breast cancer rates across different countries.
(Al-Naggar & Anil, 2016)
How Can Light at Night Cause Cancer?
The main suspect? Melatonin suppression.
Melatonin is your brain’s natural “sleep hormone” — it’s released in the dark and tells your body it’s time to rest. But when you’re exposed to light at night (especially blue light from screens and LEDs), melatonin production drops.
Reduced melatonin can:
Disrupt your circadian rhythm
Interfere with DNA repair
Influence hormone-sensitive cancers like breast and prostate cancer
This effect isn’t just theoretical. Prior studies of night-shift workers have shown increased cancer risk too, likely due to long-term melatonin disruption.
What You Can Do About It
The good news? You don’t have to live in the dark — but a few smart choices can protect your health:
Dim your lights 1–2 hours before bed
Avoid screens close to bedtime, or use blue-light filters
Use warm/red night lights instead of bright overheads
Get natural sunlight in the morning to reset your rhythm
Consider blackout curtains or a sleep mask if light leaks into your bedroom
These small steps can help preserve melatonin production and support long-term wellness.
What This Means for Sleep & Health
As sleep providers, we know that better sleep means better health. But we also know that modern habits — including overexposure to light at night — can quietly undermine your body’s natural rhythms.
If you're struggling with sleep, fatigue, or hormonal issues, it's worth examining not just your bedtime, but your lighting environment.
TL;DR
Artificial light at night is linked to higher rates of cancer, especially breast, colorectal, and lung cancer
The likely cause: melatonin suppression and circadian rhythm disruption
Small changes in your light habits can support better sleep and potentially reduce long-term health risks
Source:
Al-Naggar, R.A., & Anil, S. (2016). Artificial Light at Night and Cancer: Global Study. Asian Pac J Cancer Prev, 17(10), 4661–4664.
https://doi.org/10.22034/APJCP.2016.17.10.4661