Caffeine, Neurotransmitters, and Your Health
How Caffeine Affects Your Brain Chemistry and Well-Being
Aug 24, 2009
The caffeine molecule resembles one of the brain's neurotransmitters called adenosine. Adenosine is produced as a by-product when cells use energy, and, when it comes in contact with an adenosine receptor, dampens activity in nearby cells. Therefore, it acts as a kind of thermostat: as more adenosine is produced, more slow-down messages are received. Conversely, after an area of the brain slows down, it produces less adenosine, and receives fewer slow-down messages.
Caffeine acts in the brain by filling the same receptor spots that adenosine would occupy, but not triggering a slow-down. It does not directly stimulate the brain, but it does prevent a slowing down of brain activity. This means that while it can help you maintain performance, it probably won't make you more lively than you already are. It also means that increased doses do not result in further stimulation: caffeine is only effective in moderate doses, or doses within a person's usual tolerance. Finally, it is nearly impossible to overdose on caffeine, making it a comparatively safe stimulant.
Caffeine in High Doses
Adenosine is not the brain's only "brake", however. Because caffeine acts very precisely on a single type of neurotransmitter receptor, it does not interfere with these other aspects of our complicated brain activity. Indeed, in high doses, caffeine has been found to have the opposite of its stimulating effect in lower amounts. It is also nearly impossibly to overdose on caffeine: a lethal dose for an adult would be the equivalent of forty cups of strong coffee consumed in a short period of time -- an amount that would induce vomiting long before death.
High doses of caffeine may also improve athletic performance in some elite athletes. Caffeine appears to assist in breaking down fatty acids stored in fat cells and making them available as fuel. This effect may account for the belief that caffeine can help people lose weight. It is important to note, however, that while the process may make energy available in the body, caffeine does not actually burn any calories. Coffee-drinkers who do not exercise will find that this energy is simply re-stored as fat, resulting in little, if any, net gain.
Caffeine, Pregnancy, and Breast-Feeding
Even in adults, caffeine can take a comparatively long time to leave the body. Caffeine is broken down in the liver, and the body must dispose not only of the caffeine itself, but also the by-products of this breakdown. It takes, on average, five to six hours for half a dose of caffeine to be eliminated, though this time varies from person to person. Oral contraceptives may significantly increase this time, and it may also change during different phases of a woman's menstrual cycle. Cigarette smoking may decrease this time.
Because infants have not yet developed the liver enzymes necessary to process caffeine, it can take as long as eighty hours for a dose to leave their systems. Caffeine can be passed to an infant through breast milk, and for this reason, it recommended that women who are breast-feeding not consume caffeine.
Caffeine may also pass from a pregnant woman to the fetus, and may be associated with lower birth rates and increased risk of miscarriage or stillbirth. There may also be some link to developmental problems, and so most health care professionals advise women not to consume caffeine while pregnant or attempting to become pregnant.
Further Reading
Stephen Braun, Buzz: The Science and Lore of Alcohol and Caffeine (Oxford University Press, 1996).
