Caffeine is a bitter-tasting compound classified as a stimulant drug. It is psychoactive, meaning that is has the ability to cross the selectively penetrable blood-brain barrier and affect chemical reactions in your brain. Caffeine is present in a number of foods and beverages, including chocolate, kola nuts, tea, coffee, soft drinks and energy drinks.
Adenosine Receptors
Caffeine works by affecting the chemical receptors in your brain associated with the sleep-wake cycle. Subsequently, adenosine is one affected brain chemical, and it is involved with signaling feelings of tiredness within the brain. Caffeine is an antagonist, or something that works against adenosine, according to a study published in October 2008 in "Science Magazine." Since caffeine looks like adenosine, the adenosine receptors in the brain take in caffeine instead of adenosine. Adenosine is not detected at its receptors in the presence of caffeine.
Endothelial Health
The endothelium is the inner lining of your blood vessels. Caffeine may offer support to your endothelial function, according to evidence from animal research. A study published in August 2008 in "Arteriosclerosis, Thrombosis, and Vascular Biology" found that caffeine facilitated the renewal of endothelial cells in mice. Therefore, caffeine may help lower one of the risk factors for heart disease.
Bone Risk
Previous studies have linked caffeine to the risk of bone mineral density loss, according to the authors of a study published in July 2009 in "Medical Hypothesis." Based on the findings of their study, they propose that caffeine interferes with bone metabolism by turning on the protein kinase A pathway. Protein kinase A is an enzyme, or something that speeds up chemical reactions, with the ability to change the structure and function of proteins involved with bone metabolism, according to the authors.
Stress
Caffeine may increase your chances of feeling stressed out because it can lead to excess cortisol production. Caffeine was found to increase cortisol in a group of men and women after exercise in a study published in March 2006 in "Pharmacology Biochemistry and Behavior." Participants had 250 mg of caffeine three times spread out across the day. Based on their findings, caffeine affected cortisol in men and women differently. In women, the cortisol response to a meal after exercise was the largest factor. In men, mental stress was a bigger contributor to cortisol increase. However, with repeated doses of caffeine, the effects of gender disappeared, as men and women showed similar cortisol responses to both exercise and mental stress.
References
- "Science Magazine"; The 2.6 Angstrom Crystal Structure of a Human A2A Adenosine Receptor Bound to an Antagonist; Veli-Pekka Jaakola, et al.; 2010
- "Arteriosclerosis, Thrombosis, and Vascular Biology"; Caffeine Enhances Endothelial Repair by an AMPK-Dependent Mechanism; Ioakim Spyridopoulos, et al.; 2008
- "Medical Hypothesis"; Reciprocal Roles Between Caffeine and Estrogen on Bone Via Differently Regulating CAMP/PKA Pathway: The Possible Mechanism for Caffeine-Induced Osteoporosis in Women and Estrogen's Antagonistic Effects; Yi Zhou, et al.; July 2009
- "Pharmacology Biochemistry and Behavior"; Cortisol Responses to Mental Stress, Exercise, and Meals Following Caffeine Intake in Men and Women; William R. Lovallo, et al.; March 2006
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