Bjorngaard JH, et al. – A positive association between cigarette and coffee consumption in smokers has been reported already. Cigarette smoke increases metabolism of caffeine, so this may represent a causal effect of smoking on caffeine intake. In this current study, it was shown that higher cigarette consumption causally increases coffee intake. Researchers reported that this was consistent with faster metabolism of caffeine by smokers, but could also reflect a behavioural impact of smoking on coffee drinking.

Methods

• Researchers performed Mendelian randomization analyses in the UK Biobank (N = 114 029), the Norwegian HUNT study (N = 56 664) and the Copenhagen General Population Study (CGPS) (N = 78 650).
• They used the rs16969968 genetic variant as a proxy for smoking heaviness in all studies and rs4410790 and rs2472297 as proxies for coffee consumption in UK Biobank and CGPS.
• They also conducted analyses using linear regression and meta-analysed across studies.

Results

• Findings demonstrated that each additional cigarette per day consumed by current smokers was associated with higher coffee consumption (0.10 cups per day, 95% CI: 0.03, 0.17).
• Researchers found a weak evidence for an increase in tea consumption per additional cigarette smoked per day (0.04 cups per day, 95% CI: -0.002, 0.07).
• Data also revealed that there was strong evidence that each additional copy of the minor allele of rs16969968 (which increases daily cigarette consumption) in current smokers was associated with higher coffee consumption (0.16 cups per day, 95% CI: 0.11, 0.20), but only weak evidence for an association with tea consumption (0.04 cups per day, 95% CI: -0.01, 0.09).
• In addition, researchers found that there was no clear evidence that rs16969968 was associated with coffee or tea consumption in never or former smokers or that the coffee-related variants were associated with cigarette consumption.