Coffee intake, cardiovascular disease and all-cause mortality: observational and Mendelian randomization analyses in 95 000–223 000 individuals

International Journal of Epidemiology, 2016, 1938–1952 doi: 10.1093/ije/dyw325 Advance Access Publication Date: 29 December 2016 Original article Mendelian randomisation and instrumental variable analysis Coffee intake, cardiovascular disease and allcause mortality: observational and Mendelian randomization analyses in 95 000–223 000 individuals Ask Tybjærg Nordestgaard1,2 and Børge Grønne Nordestgaard1,2,3* 1 Department of Clinical Biochemistry and the Copenhagen General Population Study, Herlev and Gentofte Hospital, Copenhagen University Hospital, Herlev, Denmark, 2Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark and 3Copenhagen City Heart Study, Frederiksberg Hospital, Copenhagen University Hospital, Frederiksberg, Denmark *Corresponding author. Department of Clinical Biochemistry, Herlev and Gentofte Hospital, Copenhagen University Hospital, Herlev Ringvej 75, DK-2730 Herlev, Denmark. E-mail: Accepted 17 October 2016 Abstract Background: Coffee has been associated with modestly lower risk of cardiovascular disease and all-cause mortality in meta-analyses; however, it is unclear whether these are causal associations. We tested first whether coffee intake is associated with cardiovascular disease and all-cause mortality observationally; second, whether genetic variations previously associated with caffeine intake are associated with coffee intake; and third, whether the genetic variations are associated with cardiovascular disease and all-cause mortality. Methods: First, we used multivariable adjusted Cox proportional hazard regression models evaluated with restricted cubic splines to examine observational associations in 95 366 White Danes. Second, we estimated mean coffee intake according to five genetic variations near the AHR (rs4410790; rs6968865) and CYP1A1/2 genes (rs2470893; rs2472297; rs2472299). Third, we used sex- and age adjusted Cox proportional hazard regression models to examine genetic associations with cardiovascular disease and all-cause mortality in 112 509 Danes. Finally, we used sex and age-adjusted logistic regression models to examine genetic associations with ischaemic heart disease including the Cardiogram and C4D consortia in a total of up to 223 414 individuals. We applied similar analyses to ApoE genotypes associated with plasma cholesterol levels, as a positive control. Results: In observational analyses, we observed U-shaped associations between coffee intake and cardiovascular disease and all-cause mortality; lowest risks were observed in individuals with medium coffee intake. Caffeine intake allele score (rs4410790 þ rs2470893) was associated with a 42% higher coffee intake. Hazard ratios per caffeine intake allele were 1.02 (95% confidence interval: 1.00–1.03) for ischaemic heart disease, C The Author 2016; all rights reserved. Published by Oxford University Press on behalf of the International Epidemiological Association V 1938 International Journal of Epidemiology, 2016, Vol. 45, No. 6 1939 1.02 (0.99–1.02) for ischaemic stroke, 1.02 (1.00–1.03) for ischaemic vascular disease, 1.02 (0.99–1.06) for cardiovascular mortality and 1.01 (0.99–1.03) for all-cause mortality. Including international consortia, odds ratios per caffeine intake allele for ischaemic heart disease were 1.00 (0.98–1.02) for rs4410790, 1.01 (0.99–1.03) for rs6968865, 1.02 (1.00– 1.04) for rs2470893, 1.02 (1.00–1.04) for rs2472297 and 1.03 (0.99–1.06) for rs2472299. Conversely, 5% lower cholesterol level caused by ApoE genotype had a corresponding odds ratio for ischaemic heart disease of 0.93 (0.89–0.97). Conclusions: Observationally, coffee intake was associated with U-shaped lower risk of cardiovascular disease and all-cause mortality; however, genetically caffeine intake was not associated with risk of cardiovascular disease or all-cause mortality. Key words: Genetics, lifestyle, death, stroke, ischaemic heart disease, nutrition • In 95 000–223 000 individuals, coffee intake was associated with U-shaped low risk of cardiovascular disease and all- cause mortality in observational analyses, but not in genetic analyses. • Two studies from Copenhagen as well as Cardiogram and C4D international consortia were included in the genetic analyses. • Thus, genetic analyses do not support the hypothesis that coffee intake influences risk of cardiovascular disease or all-cause mortality. Introduction Coffee is one of the most widely consumed beverages in the world. Multiple observational studies including large metaanalyses have reported associations between high coffee intake and low risk of cardiovascular disease (CVD) and of all-cause mortality.1–8 However, as observational studies are often influenced by reverse causation and confounding, it is unclear whether these represent causal associations. We tested the hypothesis that high coffee intake is associated with low risk of CVD and all-cause mortality using a Mendelian randomization study design. In this design, genetic variations are used as instruments for the exposure variable, and associations between the genetic variations and the outcome variables are thus used to examine associations between the exposure variable and the outcome variables. Since genetic variations are inherited randomly at conception, reverse causation and most confounding are avoided, exactly as in a randomized, double-blind controlled trial.9 The design is based on several assumptions, including: (i) that the genetic variations are robustly associated with the exposure variable; (ii) that the genetic variations are not associated with possible confounding variables; and (iii) that the genetic variations are only related to the outcomes through the association with the exposure variable.10 Specifically, we used five genetic variations near the AHR and CYP1A1/2 genes involved in caffeine metabolism; these genetic variations have previously been associated with high caffeine intake in genome-wide association studies,11–14 and since coffee intake is the major source of caffeine consumption in Denmark, we have previously used them to examine potential effects of coffee intake on type 2 diabetes, obesity, metabolic syndrome and components thereof.15 Using 95 366 to 112 509 individuals from three Danish cohorts, we tested first whether coffee intake is associated with CVD and all-cause mortality observationally; second, whether the five genetic variations near AHR and CYP1A1/2 genes are associated with coffee intake; and third, whether the five genetic variations are associated with CVD and allcause mortality indicating causal relationships; for ischaemic heart disease (IHD), we additionally included the Cardiogram and C4D consortia in a total of up to 223 414 individuals. To test our methods, we examined associations between IHD and ApoE genotype groups using similar analytical strategies, since ApoE genotypes are associated with plasma cholesterol levels and thus would be expected to be causal (...truncated)