A groundbreaking study1 by Chinese scientists has revealed that sleep acts as a vital clean-up mechanism for the brain, clearing out harmful free radicals that accumulate during wakefulness. The findings shed new light on why sleep is essential and open doors to potential therapies for sleep disorders, especially among the elderly.
Published in Cell Metabolism on May 15, the study details how hydrogen peroxide (H₂O₂)—a reactive oxygen by-product—acts as a molecular signal that triggers the brain to enter “repair mode.” This discovery confirms a long-standing theory: the brain uses sleep to eliminate oxidative waste and restore internal balance.
The research team, led by Liu Danqian from the Centre for Excellence in Brain Science and Intelligence Technology in Shanghai (affiliated with the Chinese Academy of Sciences), demonstrated that rising levels of H₂O₂ in sleep-regulating neurons prompt the onset of sleep. This response is part of the brain’s instinctive “homeostatic regulation” mechanism—its way of maintaining internal stability.
When someone stays awake for a long time, changes build up in the brain, Our study explored how the brain perceives these changes and uses them to trigger sleep and restore equilibrium
Liu Danqian
The research builds on a theory first proposed in 1994 by pathologist E. Reimund2 of Texas Tech Medical School. Reimund suggested that free radicals—unstable, oxygen-derived molecules—accumulate during wakefulness and that sleep helps eliminate them. Although supported by early research in fruit flies, his theory couldn’t be tested in mammals until now due to technological limitations.
Using advanced monitoring techniques in mice, Liu’s team spent five years verifying Reimund’s hypothesis. They found that increasing H₂O₂ levels in sleep neurons triggered sleep, while lowering the molecule reduced sleep pressure. However, excessive levels of H₂O₂ led to fragmented sleep and brain inflammation, indicating that a balanced range is crucial for healthy rest.
Free radicals are by-products of normal metabolism but can also result from pollution, smoking, and other environmental factors. They are known to damage DNA and contribute to various diseases and signs of aging.
Now that free radicals have been shown to directly influence sleep, the findings point to antioxidant therapies as a possible treatment for age-related sleep disorders and neurodegenerative diseases like Alzheimer’s.
Too many free radicals disrupt sleep,That could explain why sleep issues are so common in older adults.
Liu Danqian
Indeed, a 2011 study3 by Harvard Medical School found that up to 50% of older people struggle with sleep, a problem linked to higher risks of illness and death.
This discovery not only deepens our understanding of the biological role of sleep but also paves the way for new strategies to address sleep disorders—particularly those tied to aging and brain health.
- Tian, Y., Kang, L., Ha, N. T., Deng, J., & Liu, D. (2025). Hydrogen peroxide in midbrain sleep neurons regulates sleep homeostasis. Cell Metabolism. https://doi.org/10.1016/j.cmet.2025.04.016 ↩︎
- Reimund, E. (1994). The free radical flux theory of sleep. Medical Hypotheses, 43(4), 231–233. https://doi.org/10.1016/0306-9877(94)90071-x ↩︎
- Crowley K. Sleep and sleep disorders in older adults. Neuropsychol Rev. 2011 Mar;21(1):41-53. doi: 10.1007/s11065-010-9154-6. Epub 2011 Jan 12. PMID: 21225347. ↩︎
