Caffeine is a most widely consumed physiological stimulant worldwide, which is consumed via natural sources, such as coffee and tea, and now marketed sources such as energy drinks and other dietary supplements. This wide use has led to concerns regarding the safety of caffeine and its proposed beneficial role in alertness, performance and energy expenditure and side effects in the cardiovascular system. The question remains "Which dose is safe?", as the population does not appear to adhere to the strict guidelines listed on caffeine consumption. Studies in humans and animal models yield controversial results, which can be explained by population, type and dose of caffeine and low statistical power. This review will focus on comprehensive and critical review of the current literature and provide an avenue for further study.

2nd Department of Internal Medicine St Anne's University Hospital and Masaryk University Brno Czech Republic

Bogomolets National Medical University Kiev Ukraine

Cardiology Center Medika St Petersburg Russia

Centre for Chronic Disease College of Health and Biomedicine Victoria University Melbourne VIC Australia

Department of Medical Biology Jessenius Faculty of Medicine Comenius University in Bratislava Martin Slovakia

Department of Pharmacology and Toxicology Faculty of Pharmacy Comenius University Odborarov 10 832 32 Bratislava Slovak Republic

Department of Physiology Masaryk University Brno Czech Republic

Division of Clinical Nutrition Faculty of Home Economics Kyoritsu Women's University Tokyo Japan

Euro Mediterranean Institute of Science and Technology Palermo Italy

Faculty of Military Health Sciences University of Defence Hradec Kralove Czech Republic

Human Anatomy Section Department of Experimental Biomedicine and Clinical Neurosciences University of Palermo Palermo Italy

Laboratory of Structural Biology and Proteomics Faculty of Pharmacy University of Veterinary and Pharmaceutical Sciences Palackeho tr 1 1946 Brno 612 42 Czech Republic

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