People have been concerned about the health effects of caffeine for some time. In 1911, for example, US agents seized 40 kegs and 20 barrels of Coca-Cola syrup under the banner of the newly established FDA. The group believed that the amount of caffeine in Coca-Cola was a public health hazard. These concerns by the federal government led to years of litigation, which was finally dropped when Coca-Cola reduced the caffeine content in the beverage.
Caffeine is a mild stimulant, and many consider this to be a beneficial side effect of the drug. It is the most commonly consumed psychoactive drug globally, and can be found in soft drinks, coffee, cocoa, tea, chocolate, energy drinks, and numerous prescription and over-the-counter drugs.
Most recently, the FDA has turned an eye to the caffeine content found in energy drinks. In 2012, the FDA opened an investigation into energy drinks after numerous reports of death in otherwise healthy individuals who consumed these products. (The lethal dose of caffeine for an average adult is considered to be about 10 g consumed at one time.) The FDA voiced concern that caffeine obfuscated “some of the sensory cues individuals might normally rely on to determine their level of intoxication.” Moreover, physicians have been cautioned to ask their patients—in particular, young men—about excessive consumption of energy drinks.
How does caffeine work?
Caffeine is absorbed via the digestive tract and permeates all body tissues. It can also cross the placental barrier between mother and fetus. Caffeine inhibits cyclic nucleotide phosphodiesterases, mildly raises norepinephrine and dopamine levels, and heightens neural activity in various brain areas. Caffeine’s effects are hypothesized to transpire due to competitive antagonism at adenosine receptors. Adenosine is a neuromodulator that is structurally similar to caffeine. Caffeine counteracts the mild sedating effects of adenosine.
Caffeine, like many other drugs, is metabolized by the cytochrome P450 1A2 (CYP1A2) pathway. Various drugs, however, can interfere with the metabolism of caffeine. Tobacco, for instance, dampens the effects of caffeine, whereas oral contraceptives increase its effects. In fact, the presence of multiple drugs in people who have died from caffeine poisoning has been attributed to the effects of these various drugs on the CYP1A2 pathway.
What are the effects of caffeine?
Drinking 4-7 cups of coffee or 7-9 cups of tea (> 500-600 mg) daily is considered a health risk and may result in caffeinism—a syndrome characterized by anxiety, restlessness, irritability, agitation, muscle tremor, insomnia, headache, sensory disturbances (eg, tinnitus), diuresis, heart symptoms (eg, tachycardia and arrhythmia), and gastrointestinal disturbances (eg, nausea, vomiting, and diarrhea). Excessive consumption of caffeine (> 400 mg/day) in women may also lead to bladder instability.
Furthermore, caffeine can interfere with calcium balance and bone metabolism, particularly in women who drink more than the caffeine equivalent of four cups of coffee per day over the course of a lifetime.
Although moderate consumption of caffeine by adults has not been linked to mood disturbance, ingesting higher levels of caffeine has been linked to anxiety—especially in people with anxiety disorders.
On the other hand, caffeine can increase alertness, vigilance, and memory, which are generally considered positive side effects of the drug. In addition, daily consumption of 2-3 cups of coffee in men has been linked to a reduction in the risk of prevalent erectile dysfunction—even among men who are overweight and obese, but not among men with diabetes.
Tolerance to caffeine’s stimulatory effects occurs quickly in those who abuse the drug. Even those who drink only 1-2 cups of coffee per day can experience fatigue and sedation upon abrupt withdrawal. Moreover, in people who drink more than this amount of coffee, headaches and nausea have been noted with cessation.