Don't have caffeine after 2 p.m.

Cost

Free. If you are used to afternoon coffee, holding off takes a little willpower.

What you get

With a pill containing 400 mg of caffeine taken 6 hours before bed (counting 107 mg for a 250 mL cup, about three or four cups of coffee), total sleep time measured by instruments was 1.1 to 1.2 hours less than with a placebo pill. A placebo pill looks the same but contains no caffeine. But the sleep diaries the subjects wrote themselves did not report a difference; they could not tell. Pooling several studies (a meta-analysis): caffeine reduced total sleep time by an average of 45 minutes. The share of time in bed actually spent asleep (sleep efficiency) fell by 7%. A 250 mL cup of coffee (107 mg) has to be finished more than 8.8 hours before bed to avoid affecting sleep.

Notes

The Drake study was done in only one lab, and its 400 mg dose is on the large side, equal to a whole day's limit taken at once; for the limit, see §2.26 (three to four cups of coffee). For people who metabolize caffeine slowly, the cutoff is even earlier. What you get back by cutting caffeine is sleep time, which adds to §3.3 (sleep 7 to 8 hours a night).

Evidence grade

A : Specific numbers from meta-analyses, large cohorts or randomized trials; for law and policy, the statute or official text.

Sources

1. Drake, Roehrs, Shambroom & Roth (2013). Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed. Journal of Clinical Sleep Medicine. https://doi.org/10.5664/jcsm.3170
2. Gardiner et al. (2023). The effect of caffeine on subsequent sleep: A systematic review and meta-analysis. Sleep Medicine Reviews. https://doi.org/10.1016/j.smrv.2023.101764

Translated from the Chinese original. Original book, section 3, tip 4. Content may be out of date and rules differ by place. When you actually deal with an agency, a doctor or a court, follow what local officials, doctors and lawyers tell you. Disclaimer