Coffee is one of the greatest widely and frequently drunk beverages globally. Epidemiological trends suggest that consumption is progressively rising due to the emergence of research indicating its varied health benefits and greater awareness of such information among laypersons. This literature review aimed to explore the relationship between coffee and health and disease, particularly whether consumption can improve blood glucose metabolism and the risk or control of diabetes mellitus. A systematic search for evidence was performed using the databases of MEDLINE and Web of Science in March 2021 using key search terms. Evidence deemed pertinent to the review was considered for inclusion. Overall, most studies found that coffee consumption with caffeine doses approaching 400 mg per day positively affected blood glucose metabolism via varied insulin-dependent and insulin-independent mechanisms. In turn, studies showed that habitual and more frequent intake of cups per day (4-6) significantly lowered the risk of type 2 diabetes than lower or absent intake. Notably, the evidence also revealed that the intake of decaffeinated coffee resulted in comparable effects on blood glucose handling, which suggests that the favorable metabolic effects of coffee are not entirely attributed to caffeine but also chemicals and minerals within coffee beans. Finally, coffee consumption with caffeine doses <400mg or <2.5mg/kg was found to be safe for children, adults, and pregnant women, with other evidence showing that adverse effects and toxicity tend to only occur with doses exceeding 2-5g caffeine.
