Dim the evening

Do this

• After sunset, switch from overhead lights to a few low lamps.
• Dim your screens. On a phone, set up the colour filter shortcut for a red screen.
• No screens in the last 30 minutes before sleep.
• Still wired after a late workout? A hot shower helps your core temperature drop.

Why it works

Evening light delays and shortens the night's melatonin. He adds that it also raises cortisol at the hour when it should be lowest, and that this affects blood sugar and the next morning's cortisol rise.

What the research says

Well supported. Ordinary room light before bed is enough to suppress melatonin, and reading on a light-emitting screen delays sleep and the body clock.

• Gooley et al., Journal of Clinical Endocrinology & Metabolism, 2011Exposure to room light before bedtime suppresses melatonin onset and shortens melatonin duration in humansRoom light in the hours before bed delayed melatonin and shortened its duration by about 90 minutes compared with dim light.
• Chang et al., PNAS, 2015Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertnessReading on a light-emitting e-reader before bed delayed the body clock, reduced evening sleepiness and lowered alertness the next morning, compared with a printed book.