Guides

What caffeine, alcohol, supplements and meal timing do to your sleep and energy, from the research, with every number cited.

• Does caffeine affect deep sleep?Yes. Pooled across studies, caffeine cut total sleep by about 45 minutes and deep sleep by about 11 minutes, and to avoid losing total sleep, a regular coffee should be finished at least 8.8 hours before bed.
• Does alcohol affect your sleep?Yes, in two directions. Alcohol helps you fall asleep faster and deepens the first half of the night, but in most studies at moderate and higher doses it cuts REM sleep, and it delays your first REM period.
• Does magnesium help you sleep?Maybe, a little. In the few small trials, magnesium helped older adults with insomnia fall asleep about 17 minutes faster, but the evidence is low quality and showed no statistically significant gain in total sleep.
• Does eating late affect your sleep?It might, but the research hasn’t settled it. Observational studies link eating close to bedtime with worse sleep quality, while controlled trials have mixed results, so your own nights are the best evidence.