The Associations Between Coffee Consumption and Metabolic Syndrome (MetS) Biomarkers Among Adults: A Systematic Review of Epidemiological Evidence

Objective To synthesize epidemiological evidence for a systematic review on the association between coffee consumption and Metabolic Syndrome (MetS)-related biomarkers, as defined by the used diagnostic framework(s), in human adult populations. This study proposes future directions for MetS-related biomarkers and coffee consumption. Methods A comprehensive search was conducted in PubMed, supplemented by manual searching, using predefined inclusion and exclusion criteria (n = 343). 13 observational studies were included in the final review. Extracted eligible studies were analyzed for adjustments, diagnostic frameworks, outcomes, and measurements. All included studies were assessed for bias using the Risk Of Bias In Non-randomized Studies – of Interventions, Version 2 (ROBINS-I V2) tool. Results Though considerable heterogeneity and modification were observed with the diagnostic framework, a majority implemented the criteria set by the National Cholesterol Education Program's Adult Treatment Panel III (NCEP ATP-III) or the International Diabetes Federation (IDF). Other variations included coffee exposure definitions, country of study, and the stratification of results by binary sex. The given evidence suggests that greater coffee consumption is associated with lower odds of elevated blood pressure (BP), increased waist circumference (WC), reduced high-density lipoprotein cholesterol (HDL-C), and elevated triglycerides (TG). From the adjusted sex-stratified results, increased coffee consumption was frequently associated with lower odds of elevated TG and increased WC in men, and elevated BP and reduced HDL-C in women. Conclusions Frequent inverse associations between coffee consumption and specific MetS components – TG and HDL-C – indicate a strong association with lipid-based metabolic outcomes. There were relatively fewer, yet still favorable, statistically significant, lower odds of elevated FBG with higher coffee consumption. Applying broader and additional measurements, such as secondary biomarkers, to assess individual biomarker levels can contribute to the principal standardization of the present heterogeneity. Limitations on additives, coffee preparation methods, and coffee quantity were observed, validating concerns from previous studies.