Do not touch caffeine after 2 p.m.

Taking 400 mg of caffeine 6 hours before bed, about three or four cups of coffee, showed up on instruments as more than 1 hour less sleep that night. A sleep diary you write yourself shows no difference at all. A 250 mL cup of coffee (107 mg) has to be finished more than 8.8 hours before bed if it is not to affect sleep. For someone who goes to bed at 11, 2 p.m. is the line.

Cost

No money. People used to afternoon coffee have to hold off; that takes a little willpower.

Benefit

Taking a tablet with 400 mg of caffeine 6 hours before bed, total sleep time measured by instruments was 1.1 to 1.2 hours less than with a placebo tablet. Counting a 250 mL cup at 107 mg, 400 mg is about three or four cups of coffee. The placebo tablet looked the same and contained no caffeine. The sleep diaries participants wrote themselves reported no difference; they could not tell. Pooling several studies: caffeine cut total sleep time by 45 minutes on average. The share of time in bed that was actually sleep (sleep efficiency) fell by 7%. A 250 mL cup of coffee (107 mg) has to be finished more than 8.8 hours before bed if it is not to affect sleep.

Notes

The Drake study was done in only one laboratory. The 400 mg it used is on the high side; it equals drinking a whole day’s ceiling at once. The ceiling is in Section 2, Item 26 (three to four cups of coffee). People who metabolize caffeine slowly need an earlier cutoff. What you get back from less caffeine is time asleep, and it stacks with item 3 (7 to 8 hours a night).

Sources · 2

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. 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. doi.org/10.1016/j.smrv.2023.101764