Caffeine short and long-term effects can be both pozitive and negative as the studies reveals. Considerations that have to be taken into account when consuming foods with caffeine quantity ingested per body weight, period of time, age, sex and personal habits.

Caffeine (1,3,7-trimethylxanthine) is a natural plant alkaloid that is widely consumed for its stimulatory effects on the central nervous system. This psychoactive compound often associated with coffee, is also an important ingredient of tea, as is theophylline, and is even found in chocolate, as a source of theobromine, kola nut, guarana seeds and yerba mate. Besides the natural sources, caffeine is found in commercial sources where it is commonly added to beverages as soft drinks, energy drinks, energy shots and caffeinated alcoholic beverages and foods like dairy products, various snacks, gums and mints, sweets and baked products. Caffeine is used also in some drugs and weight loss supplements, or it is commercialized as caffeine pill products.

 Metabolism of caffeine

After ingestion, caffeine is rapidly and completely absorbed from the gastrointestinal tract into the blood stream. The amount of time of achieving the peak plasma levels of caffeine is different from individual to individual and can vary between 15 and 120 minutes, but majority of them are reaching the high point after 30-60 minutes. Liver is the active site where caffeine is broken down into three metabolites, paraxanthine, theobromine, and theophylline. The structure of caffeine molecule is similar with the structure of adenosine molecule. In addition, caffeine binds to active sites of adenosine receptors, acting as a competitive inhibitor for adenosine; adenosine decreases the neuronal activity, inhibiting synaptic transmission and the release of neurotransmitters (promotes drowsiness, dilates blood vessels, lowers heart rate, reduces the contraction in the stomach and intestines) whereas caffeine has reverse effects.

Caffeine short-term effects

Increased blood pressure

Some studies reveal that daily consumption of coffee (250mg caffeine-3 cups of coffee) have significant changes in blood pressure and heart rate in response to caffeine in normotensive persons regarding age and gender, but no greater than hypertensive and hypertension-prone subjects.

Attention and cognition

Another short-term effect of caffeine is on the cognition and mental alertness. High levels of caffeine (200 mg and 400 mg) is improving the capacity to take advantage of alerting cues but it is causing reduction of orientating network function and decreasing the ability of using spatially-determinate cues. It is unclear the reason why caffeine is negatively acting on orientation network function and it is possible that to happen because in case of high doses of caffeine intake, individuals tend to focus more on global rather than local elements of visual scenes. 

Caffeine long-term effects

As long-term effects of caffeine can be listed: the impact on immune system, increased blood pressure and stroke and the impact in energy expenditure.

There is no clear evidence of caffeine effect on the immune system because there are not clinical test on humans due safety reasons of consumers/subjects. Anyway, scientists confirm that the caffeine-immune system relation is strongly related with the amount of caffeine intake per body weight. 

In long term, caffeine may have beneficial effect on women without history of stroke or heart diseases, who drank moderate to high amount of coffee, coffee consumption was associated with lower risk of stroke among non-smokers. As concerning energy expenditure, caffeine alone determine an increase in lipolysis and fat oxidation, and is reducing the breakdown of glycogen. As an effect caffeine potentiate the effect of ephedrine, sympathomimetic agent that is able to increase energy expenditure. Caffeine intake in low amount should be safe.

There are many considerations to take into account in terms of caffeine adverse reactions in the human body, many of them being related to the quantity ingested per body weight, period of time, age, sex, beverages/food content, and personal habits. Moreover, caffeine can be considered a safe thermogenic agent for losing weight. Most of the energy drinks have caffeine levels between 75 to 174 mg per serving, whereas higher caffeine energy drinks have levels of caffeine greater than 500 mg per serving in which case can cause insomnia, nervousness, headache, and tachycardia. The short-term lethal dose of caffeine for adults is estimated to be around 5-10 g per day (75 cups of coffee, 125 cups of tea, 200 cola beverages) while long-term moderated dose of caffeine have minor adverse effects on human health.