If you have difficulty falling asleep before midnight, even when you feel very tired, or if you often feel like your sleep quality is poor, regardless of how long you sleep, it is likely that excessive nocturnal cortisol is interfering with your slumber. Cortisol, a kind of stress hormone, impairs brain cells’ utilization of glucose, the main fuel for the cells. When the brain’s fuel supply is interrupted by high cortisol levels, impairment of learning, memory, and mood can result. What’s more, this reduction in energy supply to brain cells weakens them, which may cause or aggravate dementia, and deteriorates the hunger centre in your brain, which can make you eat more than necessary.