"The most obvious influence on hormones is insomnia,” says Dr Carmine Pariante, reader in biological psychiatry at the Institute of Psychiatry, King’s College, London.
- Lack of sleep increases levels of cortisol and cytokines, the immune system’s “fight or flight” stress-response hormones.
- Cytokines tell cells to protect us from infection. However, an elevated level of cytokines is also linked to depression – possibly because they can reduce levels of tryptophan, a substance from which we produce serotonin, the brain chemical that influences our mood.
- Meanwhile, the highest levels of cortisol are naturally released in the morning to wake up the body, but if its rhythms are upset this can cause tiredness, low energy, sleep disturbances and irritability.