It’s important to know that caffeine is an addictive drug. Among its many actions, it operates using the same mechanisms that amphetamines, cocaine, and heroin use to stimulate the brain. Relatively speaking, caffeine’s effects are milder than amphetamines, cocaine and heroin, but it is manipulating the same channels in the brain, and that is one of the things that gives caffeine its addictive qualities.
As adenosine is created in the brain, it binds to adenosine receptors. The binding of adenosine causes drowsiness by slowing down nerve cell activity. In the brain, adenosine binding also causes blood vessels to dilate, most likely to let more oxygen in during sleep.
To a nerve cell, caffeine looks like adenosine. Caffeine therefore binds to the adenosine receptor. However, it doesn’t slow down the cell’s activity like adenosine would. As a result, the cell can no longer identify adenosine because caffeine is taking up all the receptors that adenosine would normally bind to. Instead of slowing down because of the adenosine’s effect, the nerve cells speed up. Caffeine also causes the brain’s blood vessels to constrict, because it blocks adenosine’s ability to open them up. This effect is why some headache medicines like Anacin contain caffeine — if you have a vascular headache, the caffeine will close down the blood vessels and relieve it.
So, now you have increased neuron firing in the brain. The pituitary gland sees all of this activity and thinks some sort of emergency must be occurring, so it releases hormones that tell the adrenal glands to produce adrenaline (epinephrine). Adrenaline is the “fight or flight” hormone, and it has a number of effects on your body:
- Your pupils dilate.
- Your breathing tubes open up (this is why people suffering from severe asthma attacks are sometimes injected with epinephrine).
- Your heart beats faster.
- Blood vessels on the surface constrict to slow blood flow from cuts and also to increase blood flow to muscles.
- Blood pressure rises.
- Blood flow to the stomach slows.
- The liver releases sugar into the bloodstream for extra energy.
- Muscles tighten up, ready for action.
This explains why, after consuming a big cup of coffee, your hands get cold, your muscles tense up, you feel excited and you can feel your heart beat increasing.
Caffeine also increases dopamine levels in the same way that amphetamines do. Dopamine is a neurotransmitter that activates pleasure centers in certain parts of the brain. Heroin and cocaine also manipulate dopamine levels by slowing down the rate of dopamine reabsorption. Obviously, caffeine’s effect is much lower than heroin’s, but it is the same mechanism. It is suspected that the dopamine connection contributes to caffeine addiction.
The problem with caffeine is the longer-term effects, which tend to spiral. For example, once the adrenaline wears off, you face fatigue and depression. So what are you going to do? You consume more caffeine to get the adrenaline going again. As you might imagine, having your body in a state of emergency all day long isn’t very healthy, and it also makes you jumpy and irritable.
The most important long-term problem is the effect that caffeine has on sleep. Adenosine reception is important to sleep, and especially to deep sleep. The half-life of caffeine in your body is about six hours. That means that if you consume a big cup of coffee with 200 mg of caffeine in it at 3:00 p.m., by 9:00 p.m. about 100 mg of that caffeine is still in your system. You may be able to fall asleep, but your body will probably miss out on the benefits of deep sleep. That deficit adds up fast. The next day you feel worse, so you need caffeine as soon as you get out of bed. The cycle continues day after day.
Coffee is the most popular beverage in the world, with more than 400 billion cups consumed each year. More than 450 million cups of coffee are consumed in the United States every day.
- About half of the people in the United States over the age of 18 (that’s 107 million) drink coffee every day. On average, each coffee drinker consumes three and a half cups each day.
- As early as the ninth century, people in the Ethiopian highlands were making a stout drink from ground coffee beans boiled in water.
- Coffee is grown in more than 50 countries in South America, Central America, Asia, Africa, and the Caribbean.
- In 1971, a group of Seattle-based entrepreneurs opened a coffee shop called Starbucks. Today there are more than 6,000 Starbucks outlets in the United States. The chain also operates stores in 36 other countries.
- Nearly 25 million farmers worldwide depend on coffee crops for their economic livelihood.
- Coffee contains caffeine, the stimulant that gives you that “lift.” Caffeine is the most popular drug in the world, and 90 percent of people in the United States consume it in some form every day.
- Despite what you may believe, dark-roast coffee has less caffeine than coffee that’s been lightly roasted.
- Scandinavia boasts the highest per-capita coffee consumption in the world. On average, people in Finland drink more than four cups of coffee a day.
- After oil, coffee is the world’s second-most-valuable commodity exported by developing countries. The global coffee industry earns an estimated $60 billion annually.
The most serious impact of coffee cultivation continues to be the conversion of natural forest areas to plant coffee. The large, monocrop plantations typical of full-sun plantations cause the greatest reductions in biodiversity. Studies in Colombia and Mexico indicate that full-sun coffee plantations support 90% fewer bird species than shade-grown coffee.
Even with shade coffee the number of tree species can be reduced by 80% or more. Mammals and reptiles show declines in populations and species diversity relative to natural forests.
– from howstuffworks, health.howstuffworks