Oh caffeine, the sweet elixir of life!

Caffeine occurs naturally in over 60 plant species and is present in so many popular drinks that it is very likely the most widely consumed of behaviorally active substances/drugs.  And as my students know from personal observations, it is extremely rare to see me without my coffee mug in hand.  So count me among the caffeine indoctrinated.  What we know is that caffeine has many pharmacological targets throughout the human body.  However when it comes to our brains, the normal consumption levels of caffeine seem to primarily block adenosine receptors A1 and A2A and/or interact directly with ion channels that are responsible for regulating calcium levels and various inhibitory neurotransmitters (i.e. GABA and glycine).   Caffeine has many potentially beneficial and/or negative effects on brain function that includes sleep, memory, cognition, mood, performance, and more.  It also has specific effects on Parkinson’s disease, seizures, ischemia, stress levels, and brain development.  Caffeine can also improve the effectiveness of aspirin or acetaminophen, and when used with a drug called ergotamine can be effective at treating cluster and migraine headaches.

Many of us use caffeine to combat tiredness, yet research in the area of sleep is somewhat divergent and contradictory.  From research data, caffeine is currently viewed more as an agent to regulate sleep quality than as a substance that disturbs sleep and counters sleepiness.  In fact concerning sleep quality, caffeine seems to have very few negative effects.  As for behavioral arousal, caffeine has been shown to decrease reaction times and improve performance on tasks (i.e. selective attention). This suggests strongly that caffeine increases alertness, physiological arousal, and in low doses positive moods/affect.  However, as with any drug, high doses can have considerable negative effects.  Yet what constitutes a high dosage has considerable individual variability based on genetic predispositions and prior experience with caffeine consumption.  Caffeinism is the term given to “intoxication” or dependence upon caffeine, which has the potential to exacerbate anxiety disorders.  Moreover, it can affect depression, schizophrenia, eating disorders, ADHD, and restless legs syndrome.

Perhaps one of the more interesting results from caffeine

research is that the data thus far suggest it provides protective effects for dopaminergic neurons, which may in fact help in preventing the onset of Parkinson’s disease (PD).    In Parkinson’s disease, the dopamine producing neurons (seen on the right) deteriorate and can no longer send signals to skeletal muscles. What results is the characteristic symptoms of tremors, difficultly walking (i.e. gait alterations), slow movements and coordination issues.  Recent epidemiological studies have shown the common consumption of coffee or other caffeinated beverages reduces one’s risk of developing PD later in life.  The thought is that caffeine provides the protective  effect by binding to that adenosine A2A receptor mentioned previously.  The antagonistic effect results in protection of dopaminergic neurons and others from degeneration and death.

When caffeine is consumed at reasonable levels it should not be a concern for human health.  However caffeine is not all rainbows and sunshine especially when administered at high acute dosages.  At high doses it could lead to aggravation of neuronal damage from conditions such as a stroke or even extend the life of a seizure.  Outside of the brain, it can increase blood pressure by causing vasoconstriction, so those at risk of heart disease or with hypertension should be cautious of their caffeine use.  With this said though, an overdose on caffeine is estimated to be around 150 to 200 milligrams per kilogram, or more relative to something we recognize is that  it would be the consumption of roughly 80 to 100 cups of coffee a day.  Now I love my coffee, but not even on the best of days could I dream of approaching those numbers.  The average cup of coffee contains around 100-250 mg/L of caffeine, but with the increasing popularity of energy drinks the high dose numbers become attainable.  For example, 5-hour Energy drinks have a caffeine content upwards of 2000 mg/L (or 200mg/bottle).   And as many countries are beginning to recognize, these drinks have health risks at the higher dosages and have begun to increase regulations upon them to protect children and adolescents.  So as with anything in our diets, ingest caffeine in moderation.