Caffeine, alcohol and sleep

Caffeine can disturb sleep even 6 hours before bed, and alcohol tends to break up the second half of the night. The NHS advises no alcohol, tea or coffee for at least 6 hours before bed. A diary shows whether it's true for you.

Caffeine

In a 2013 study, people took 400 mg of caffeine, a large dose, at bedtime, 3 hours before or 6 hours before. All three disturbed sleep compared with a placebo. Even at 6 hours, caffeine cut measured sleep by more than an hour. The authors concluded it supports avoiding substantial caffeine for at least 6 hours before bed.

The study doesn't tell you what one afternoon cup does to you, and the authors note that how quickly people clear caffeine varies a lot, so advice on when to stop ranges from 4 to 11 hours before bed. Tea and cola contain caffeine too.

Alcohol

A 2013 review of all known studies of alcohol and sleep in healthy volunteers found the same pattern at all doses: people fell asleep faster and slept less brokenly in the first half of the night, then had more disturbed sleep in the second half. If a drink helps you drop off but you wake at 03:00 or 04:00, that fits the pattern.

Testing it on your own nights

General advice is a starting point. Your diary can show whether late caffeine or a drink goes with your bad nights:

1. For two weeks, write down cups of coffee, tea or cola, the time of the last one, and alcoholic drinks, alongside each night.
2. Compare the nights with and without each one: sleep quality, time to fall asleep, time awake and sleep efficiency.
3. Then change one thing, such as no caffeine after 14:00, for another two weeks and compare again.

A handful of nights can mislead, so look at how many nights each comparison is based on before deciding.

The American Academy of Sleep Medicine's insomnia guideline lists caffeine and alcohol among the things a sleep log can record, so they're worth taking to a doctor too.

This guide isn't medical advice. If poor sleep has gone on for months or makes the day hard to cope with, see your doctor.