Light exposure during sleep associated with cardiometabolic effects and impaired sleep physiology
| Citation | Mason IC, Grimaldi D, Reid KJ, et al. Light exposure during sleep impairs cardiometabolic function. PNAS. 2022;119(12):e2113290119. |
|---|---|
| Study type | Randomized trial |
| Population | Healthy young adults in a laboratory sleep setting |
| Sample | 20 participants |
| Primary source | https://doi.org/10.1073/pnas.2113290119 |
Headline finding
One night of sleeping in moderate room light (100 lux) versus dim light (<3 lux) increased nighttime heart rate, decreased heart-rate variability, and increased next-morning insulin resistance.
Limitations
- Small laboratory study of healthy young adults over a single night — long-term real-world effects are extrapolation.
- 100 lux is brighter than many bedrooms; effects at lower light levels are less clear.
Why this evidence label
A controlled human experiment with physiological endpoints, consistent with larger observational literature on light at night — but small and short.
Editorial note
A tidy controlled demonstration that the sleeping body registers room light: autonomic arousal during sleep and measurably worse glucose handling the next morning, after a single night.
Why we cite it: it’s the experimental backbone of the “darkness is the cheapest win” ranking in our sleep environment guide.
Reviewed by Sonic Vitality Editorial on July 12, 2026 . See our methodology and corrections policy.