Investigating genetic correlations and causal effects between caffeine consumption and sleep behaviours

Jorien L. Treur*, Mark Gibson, Amy E. Taylor, Peter J. Rogers, Marcus R. Munafò

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

13 Citations (Scopus)
461 Downloads (Pure)


Observationally, higher caffeine consumption is associated with poorer sleep and insomnia. We investigated whether these associations are a result of shared genetic risk factors and/or (possibly bidirectional) causal effects. Summary-level data were available from genome-wide association studies on caffeine intake (n = 91 462), plasma caffeine and caffeine metabolic rate (n = 9876), sleep duration and chronotype (being a “morning” versus an “evening” person) (n = 128 266), and insomnia complaints (n = 113 006). First, genetic correlations were calculated, reflecting the extent to which genetic variants influencing caffeine consumption and those influencing sleep overlap. Next, causal effects were estimated with bidirectional, two-sample Mendelian randomization. This approach utilizes the genetic variants most robustly associated with an exposure variable as an “instrument” to test causal effects. Estimates from individual variants were combined using inverse-variance weighted meta-analysis, weighted median regression and MR-Egger regression. We found no clear evidence for a genetic correlation between caffeine intake and sleep duration (rg = 0.000, p =.998), chronotype (rg = 0.086, p =.192) or insomnia complaints (rg = −0.034, p =.700). For plasma caffeine and caffeine metabolic rate, genetic correlations could not be calculated because of the small sample size. Mendelian randomization did not support causal effects of caffeine intake on sleep, or vice versa. There was weak evidence that higher plasma caffeine levels causally decrease the odds of being a morning person. Although caffeine may acutely affect sleep when taken shortly before bedtime, our findings suggest that a sustained pattern of high caffeine consumption is more likely to be associated with poorer sleep through shared environmental factors. Future research should identify such environments, which could aid the development of interventions to improve sleep.

Original languageEnglish
Article numbere12695
Number of pages9
JournalJournal of Sleep Research
Issue number5
Early online date22 Apr 2018
Publication statusPublished - 1 Oct 2018

Structured keywords

  • Brain and Behaviour
  • Nutrition and Behaviour
  • Physical and Mental Health


  • 1,3,7-Trimethylxanthine
  • duration of sleep
  • genetic overlap
  • instrumental variable analysis
  • sleeplessness
  • ‘morningness’


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