Occurring naturally in more than 60 plants, caffeine is a bitter substance that when consumed has stimulant properties. According to neurologist Dr. R. E. Shapiro of the University of Vermont, caffeine is the most widely consumed stimulant drug in the world. Caffeine induces feelings of alertness and increased energy as a result of its interactions with adenosine receptors in the brain. Caffeine is also commonly added to pain relief medication because of the role of adenosine in headaches and migraines.
A chemical in the central nervous system, adenosine regulates your cycles of sleeping and waking. When you are awake, adenosine accumulates in the brain and eventually causes drowsiness by attaching to cells in the basal forebrain and inhibiting their activity. Adenosine stimulates signals that tell your body it is time to rest, and activates the responses necessary to engage in full and sustained sleep.
Caffeine and Adenosine
Caffeine's effects of increasing energy and making you feel more alert are due to its interaction with adenosine receptors in the brain. Both caffeine and adenosine are neurotransmitters belonging to a chemical group known as xanthine. In your brain, caffeine appears as adenosine to nerve cells and is able to bind to adenosine receptor sites. As a result, your brain does not detect adenosine, and nerve activity does not slow down. Instead, caffeine increases brain activity, making you feel more energetic and less sensitive to your body's natural rhythms of wakefulness and sleep.
Caffeine and the Central Nervous System
Your body responds to blocked adenosine by increasing neural activity, which in turn stimulates the pituitary gland. The pituitary gland transmits signals to prepare your body for increased activity and also activates the release of adrenaline from the adrenal gland. Adrenaline induces a number of responses throughout your body that make you feel more awake and alert. The liver releases greater amounts of sugar into the bloodstream to increase energy, your pupils dilate, your heart rate accelerates and your breathing tube opens in order to take in more oxygen. While limited periods of heightened adrenaline are natural and serve important protective purposes in your body, sustained high levels can be damaging to your physical and emotional health.
Caffeine, Adenosine and Pain
Caffeine is a common ingredient in acetaminophen-based pain relievers because it constricts blood vessels at the adenosine receptor site. In his August 2008 review article on the relationship between caffeine and pain, Dr. Shapiro indicates that adenosine is an important factor in headaches and migraines, but its exact role is poorly understood; however, while caffeine can help relieve pain, it can also have the opposite effect. With regular consumption, your central nervous system develops a dependency on the substance that can produce painful experiences of withdrawal. Like a headache or migraine, caffeine withdrawal symptoms can include dizziness, sharp head pains, sensitivity to noise, anxiety and irritability. Excessive caffeine intake can also disrupt sleep patterns, heart rate and mood.