What does sleep deprivation do to your immune system?

Sleep deprivation weakens the immune system on several fronts at once. Both the fast, innate part of the immune system (which responds immediately to invaders) and the slower, adaptive part (which produces targeted antibodies) function less well when you structurally or acutely get too little sleep. The result is a demonstrably higher risk of infections and a weaker response to vaccinations. This is one of the most consistently demonstrated effects on the immune system, supported by multiple human studies.

Beyond a weakened defence against pathogens, chronic sleep deprivation also triggers an overactive side: a smouldering, body-wide inflammation. That may sound contradictory, but the immune system becomes dysregulated in a sense: less capable of fighting infections, yet simultaneously in a state of permanent low-level 'smouldering'. Elevated levels of pro-inflammatory signalling molecules (cytokines) have been measured in multiple sleep deprivation studies. Over the longer term, this low-grade inflammation contributes to conditions such as type 2 diabetes, atherosclerosis, and possibly also brain diseases.

An association has also been found with a process called 'trained immunity': sleep deprivation may activate a kind of overactive immune memory in bone marrow stem cells that contributes to the development of atherosclerosis. This evidence is for now associative, not proven causal, and warrants further research in humans.

For people who exercise or perform physically demanding work, sleep plays an additional role. Sleep deprivation slows the recovery from muscle damage after exertion, partly because the local immune regulation around damaged muscles becomes disrupted. Growth hormone signals (such as IGF-I) that help repair muscle tissue are also negatively affected.

The reverse reasoning has been investigated as well: sufficient sleep actively supports the immune defence. People who sleep well respond better to vaccinations and recover more quickly from infections. This makes sleep relevant not only as something that prevents damage, but also as a positive lever for better immune function. Sleep problems such as chronic insomnia are furthermore associated with accelerated cellular ageing through that same smouldering inflammation, although this link is largely associative.