Temperature, meals, alcohol, caffeine, exercise

1. Temperature

Falling asleep requires a drop in core temperature of about one degree Celsius. Anything that prevents that drop delays sleep.

Bedroom: 17 to 19 °C, or 63 to 66 °F. That is colder than most people run their bedrooms, and it is one of the most effective settings there is.

The paradoxical hot shower. A hot shower or bath sixty to ninety minutes before bed speeds up falling asleep. The mechanism: the heat causes peripheral vasodilation, and the heat loss that follows drops core temperature faster than it would have fallen on its own.

Extremities. Sticking your feet out from under the duvet helps heat escape. Conversely, cold feet prevent sleep onset: thin socks, counter-intuitively, work for a lot of people.

2. Meals

Last meal two and a half to three hours before bed. Digestion raises core temperature and engages the nervous system.

Evening composition: complex carbohydrates and light protein. A very fatty or very heavy meal degrades deep sleep.