To start with the bad news: yes, being chronically sleep deprived is pretty bad for us. One sobering and relatively recent discovery is the glymphatic system, a waste-clearance mechanism that flushes “misfolded” proteins like beta-amyloids (found in the brains of people with Alzheimer’s disease) from the brain during rest. Foster points to data showing that poor sleep during the middle years is a risk factor for dementia in later years, because the brain loses its ability to effectively clear these toxins. “There’s increasing evidence surrounding a lack of sleep’s association with cognitive decline later in life,” says Prof Guy Leschziner, a consultant neurologist who specialises in sleep disorders. “But it’s also associated with increased risk of cardiovascular disease and stroke. We also know that it impacts a range of other physiological processes, like your immune system, your respiratory system and so on. It even influences how your brain processes pain signals, and makes you more vulnerable to them. Every single system is influenced by sleep in some way.”