A light box eased daytime sleepiness in Parkinson’s disease
STUDY: Li HX et al, Nat Sci Sleep 2026
STUDY TYPE: Randomized, crossover pilot trial
FUNDING: Chinese government and academic research grants
Background
Parkinson’s disease disrupts sleep in 75% of patients, causing insomnia, restless legs, fragmentation, daytime fatigue, and even REM sleep behavior disorder (acting out dreams). Morning light sets the circadian clock, supports energy production through the mitochondria, and may enhance dopamine signalling.
Past studies show benefits for sleep and possibly movement in Parkinson’s, and this small one adds to the picture.
The Study
- 27 adults with Parkinson’s disease and sleep complaints (Hoehn and Yahr stage 1 to 3).
- Randomized crossover: bright light (10,000 lux) vs. dim light (200 lux, control), 30 days each, with a 30-day washout.
- Light was delivered twice daily for one hour each session (between 8:00-11:00 AM, and 5:00-7:00 PM)
- Sleep was assessed with clinical scales, overnight sleep studies, and brain MRI.
Results
Bright light reduced the Epworth Sleepiness Scale scores more than dim light (difference -2.65 points, p=0.012), a moderate-to-large effect. Other sleep questionnaires didn’t differ between conditions.
On overnight sleep studies, bright light reduced tonic REM sleep without atonia, a marker for REM sleep behavior disorder (-4.22%, p=0.002). Sleep stages were unchanged, and brain scans showed no differences after correction for multiple comparisons.
Side Effects
One patient had transient itching during dim light that resolved on its own; no other adverse events occurred.
Limitations
Small, cross-over design.
Practice Implications
- Light therapy is a reasonable, low-risk add-on for daytime sleepiness in Parkinson’s disease. It may also improve motor symptoms, though the studies on this are not conclusive.
- With all these auxiliary benefits, consider light therapy for depression in Parkinson’s. Here are clinically tested boxes.
—Chris Aiken, MD
Director, Psych Partners
Editor in Chief, Carlat Psychiatry Report
