Caffeine - Not just a stimulant (Review)

Journal Title (Medline/Pubmed accepted abbreviation): Nutrition.
Year: 2010
Volume: 26
Page numbers: 932-938
doi (if applicable): 10.1016/j.nut.2010.08.004

Summary of Background and Research Design

Hypothesis/Research Question:Based on current literature, what are the effects of caffeine on whole body physiology and performance? What are the safety issues surrounding caffeine?

Summary of article:
This article reviews the effects of caffeine on a number of different physiological and human performance endpoints. The safety of caffeine was also evaluated. In general, the author came to these conclusions regarding moderate intakes of caffeine: 1) increased energy availability; 2) increased daily energy expenditure; 3) decreased fatigue; 4) decreased sense of effort associated with physical activity; 5) enhanced physical performance; 6) enhanced motor performance; 7) enhanced cognitive performance; 8) increased alertness, wakefulness, and feelings of “energy”; 9) decreased mental fatigue; 10) quickened reactions; 11) increased accuracy of reactions; 12) increased ability to concentrate and focus attention; 13) enhanced short-term memory; 14) increased ability to solve problems requiring reasoning; 15) increased ability to make correct decisions; 16) enhanced cognitive function capabilities and neuromuscular coordination; and 17) caffeine is safe in otherwise healthy, nonpregnant adults.

Interpretation of findings/Key practice applications:

Moderate caffeine intake was never really defined in this article. However most of the studies of performance-enhancing benefits that were reviewed had employed doses of caffeine that were <= 600 mg. In concordance with this, other review articles on this topic have supported the ergogenic effects in a number of sports associated with doses of 3-6 mg/kg body weight (210-420 mg for a 70 kg person), with no additional benefits above this level.

Limitations of the research:

The studies discussed in this article, in general, were those showing a positive effect of caffeine. As such, some might question the comprehensiveness and/or objectivity of this review. There were a number of issues that were briefly mentioned that could have been addressed or addressed more fully, including: 1) the effects of adaption to habitual caffeine use and the effects of a brief period of abstention followed by resumption of caffeine use; 2) the effects of caffeine on overall fluid balance in exercising athletes; 3) potential safety issues associated with the interaction of caffeine and other dietary supplements; and 4) potential safety concerns with caffeine in persons with heart arrhythmias, which are typically episodic in nature and may be undiagnosed. A further point of interest is that the author addressed caffeine as a phytonutrient, although many nutritionists might question whether caffeine is, in fact, a phytonutrient. There is no known physiologic system that is dependent on either caffeine or one of its metabolites and persons can maintain complete health indefinitely without a source of caffeine.
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