We spend a third of our lives asleep, and science still does not really know why. A new theory, published in September 2026, puts mitochondria at the heart of the answer: sleep would be, in part, the time when our energy plants do the cleaning.
A question still open
We know what lack of sleep does: flagging attention, less reliable memory, more fragile mood. We know less about what, in the brain, calls for sleep. An international team proposes in the journal Frontiers in Psychiatry a "mitochondrial theory of sleep", which brings together results obtained in humans, in animals, and in large genetic databases.
Their starting point is simple. Neurons use a huge amount of energy while we are awake. This intense work produces waste, in particular oxidising molecules, and upsets the calcium balance in cells. And these three elements, energy, oxidising waste and calcium, are precisely what mitochondria manage.
Nine genes where sleep and energy meet
By cross-referencing several databases, the authors identified nine mitochondrial genes linked at once to energy production, to the functioning of connections between neurons and to sleep characteristics. According to their model, lack of sleep goes along with disrupted energy production and a build-up of these oxidising molecules. Sleep would give mitochondria the time to restore the balance.
A study published in July 2026 in the journal PNAS points the same way, in the fruit fly: sleep deprivation there triggers, via the mitochondria of certain immune cells, a wave of oxidative stress that eventually reaches the brain. In these flies, blocking this mechanism extends survival under chronic sleep loss.
What to make of it
The authors say so themselves: most of the data are correlations, and their theory is a framework to be tested, not an established truth. The fly study, for its part, remains far from humans. But this lead has the merit of connecting scattered observations, and of reminding us that sleep is not wasted time: it is a time of repair, down to the level of the cell.
Key points
- While awake, the brain uses a lot of energy and accumulates oxidising waste.
- A new theory proposes that sleep lets mitochondria put things back in order.
- The evidence remains mostly indirect or from animal studies.
- Sleep increasingly appears as an active time of repair.
Sources
- Pandi-Perumal SR, Paul S, Saravanan KM et al. The mitochondrial theory of sleep: an integrative framework for understanding sleep-wake regulation. Frontiers in Psychiatry, 2026. https://doi.org/10.3389/fpsyt.2026.1922556
- Zhang Y, Lee JH, Yu Z et al. Dopamine-driven mitochondrial reverse electron transport in immune cells mediates gut-brain ROS signaling during sleep deprivation. PNAS, 2026. https://doi.org/10.1073/pnas.2530907123
