Caffeine comes from coffee beans, but it can also be synthesized in a laboratory. It has the same structure whether it’s in coffee, energy drinks, tea or pills.

Caffeine is a powerful stimulant, and it can be used to improve physical strength and endurance. It is classified as a nootropic because it sensitizes neurons and provides mental stimulation.

Habitual caffeine use is also associated with a reduced risk of Alzheimer's, cirrhosis, and liver cancer.

Caffeine’s main mechanism concerns antagonizing adenosine receptors. Adenosine causes sedation and relaxation when it acts upon its receptors, located in the brain. Caffeine prevents this action and causes alertness and wakefulness. This inhibition of adenosine can influence the dopamine, serotonin, acetylcholine, and adrenaline systems.

Habitual caffeine use leads to tolerance. This means the effects of caffeine will be diminished, often to the point where the only benefit a user experiences is caffeine’s anti-sleep effect. This is an ‘insurmountable’ tolerance, which means more caffeine will not overcome it. A month-long break from caffeine will reduce tolerance.

To evaluate the associations between coffee and caffeine consumption and various health outcomes, the annual reviews association performed an umbrella review of the evidence from meta-analyses of observational studies and randomized controlled trials (RCTs).

Of the 59 unique outcomes examined in the selected 112 meta-analyses of observational studies, coffee was associated with a probable decreased risk of breast, colorectal, colon, endometrial, and prostate cancers; cardiovascular disease and mortality; Parkinson's disease; and type-2 diabetes.

Of the 14 unique outcomes examined in the 20 selected meta-analyses of observational studies, caffeine was associated with a probable decreased risk of Parkinson's disease and type-2 diabetes and an increased risk of pregnancy loss.

Of the 12 unique acute outcomes examined in the selected 9 meta-analyses of RCTs, coffee was associated with a rise in serum lipids, but this result was affected by significant heterogeneity, and caffeine was associated with a rise in blood pressure.

Given the spectrum of conditions studied and the robustness of many of the results, these findings indicate that coffee can be part of a healthful diet.

The Human Effect Matrix from summarises human studies to tell you what effects Caffeine has on your body, how much evidence there is, and how strong these effects are.

Anaerobic cardiovascular exercise: Caffeine appears to benefit anaerobic cardiovascular exercise, perhaps due to combination antifatigue effects and increasing power output.

Power output: There appears to be a reliable and significant increase in power output (both weight lifting as well as cycle ergometer measurements) in both trained and sedentary persons with doses of caffeine exceeding 5 mg/kg, assuming the subject is not caffeine tolerant. Tolerance, or lower doses of caffeine, are not as effective.

Wakefulness: Caffeine is reliable and effective in increasing the state of wakefulness and suppressing sedation.

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