The half life of caffeine determines how long the stimulant remains in the body. It varies from person to person, but it can take several hours for caffeine to be eliminated. That can be good or bad, depending on when you take it. If you have more than your usual dose late in the day, it can lead to a night of tossing, turning and no sleep.
It’s impossible to tell coffee’s exact half-life because it differs so much from person to person. A half-life is the time it takes for one-half of the amount of a substance to be eliminated from the body. For example, if you consume 200 mg of caffeine, the half-life is the amount of time until you have just 100 mg left in you.
An interesting article titled Caffeine Pharmacology on http://www.news-medical.net says:
The half-life of caffeine … varies widely between people, depending on factors such as age, body weight, pregnancy status, medication intake and liver health. In healthy adults, the half-life is approximately 5 to 6 hours. Heavy cigarette smoking can decrease the half-life of caffeine by up to a half, and in pregnancy the half-life may be increased by as much as 15 hours.
Caffeine’s stimulating properties start as soon as 15 minutes after taking it and can last up to six hours. It reaches its peak concentration in the blood about 15 to 120 minutes after ingestion. Taken in moderate amounts, caffeine increases alertness and decreases sleepiness, the article says.
The article points out caffeine’s other benefits, including
Many people stop taking caffeine, whether in beverages, medicines, candy or supplements, well before bedtime. And it takes up to 12 hours to clear it from the body. James Lane, an emeritus professor at Duke University School of Medicine in North Carolina, told Live Science that the timing makes it more likely that people will develop a dependency on caffeine because they want to drink it the next day when they wake up. The article states:
The reason people who regularly drink caffeine wake up feeling groggy, confused or with a headache is that they are experiencing withdrawal symptoms from yesterday’s coffee, Lane said. These withdrawal symptoms are relieved when they get their morning fix of caffeine.
The University of Rochester’s University Health Service publishes a health topics PDF titled simply Caffeine that states:
Caffeine’s strongest effects are felt for about an hour after taking it, but some effects last 4 to 6 hours. Caffeine causes increased neuron firing in the brain, which the pituitary gland perceives as an emergency and therefore causes the adrenal glands to release adrenaline. Caffeine also increases dopamine levels, the neurotransmitter that is affected by drugs like amphetamines and heroin. Obviously, it does this on a much lower level than those drugs, but this may be the source of caffeine’s addictive quality. While caffeine is mildly addictive, it has not been shown to have a direct link with any serious health risks.
When we talk about the “half life” of a substance, people might be nervous because the term is closely associated with poisons and nuclear radiation. But half life is a medical term too, and even the most benign or beneficial substances have half lives.
Caffeine is considered safe when taken in moderation. What is considered a moderate dose? The European Food Safety Authority in 2015 said caffeine intake of up to 400 mg a day, or single doses of 200 mg, is safe for adults.
The professional journal Coffee & Health states:
EFSA also advised that single doses of 100 mg of caffeine may increase sleep latency and reduce sleep duration in some adult individuals, particularly when consumed close to bedtime.
To determine how much caffeine the products you consume contain, consult this table from the University of Rochester:
Please note that some other products, including energy drinks, supplements, candies and some medications, contain caffeine. Read the label of the product you are about to consume carefully.
Medical experts caution pregnant women to limit caffeine intake to 200 mg per day to avoid lower birth weights and risk of miscarriage.
Coffee & Health also advises all people to take moderate amounts of caffeine to avoid unpleasant side effects. The article states:
As with many elements of our daily diet, over-consumption may in some people lead to unwanted side effects. Most people consume a level of food or drink that they are comfortable with and therefore would not experience such effects. However, those who do not self-moderate their intakes of caffeine, may experience feelings of anxiety, hyper-activity, nervousness and sleep disturbance.
Whatever the half life, people do build up a tolerance for caffeine that reduces the stimulating and invigorating effects of the world’s most popular mood-altering substance.
Caffeine Informer has an excellent article on caffeine tolerance.It says a first-time user or someone who has been off of caffeine for a long time has zero tolerance. These people get the maximum effects of euphoria, alertness, good mood and increased energy and motivation.
To reset the tolerance to zero, the article says a person should do a caffeine cleanse by not ingesting it for between two weeks to two months. Then, don’t let caffeine dependence develop again by not consuming it too regularly.
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U.S. National Public Radio published a February 2016 story titled "Caffeine for Sale: The Hidden Trade of the World's Favorite Stimulant" about how caffeine is removed from coffee beans and then where it goes after the decaf coffee is made.
Now there is a huge, worldwide trade in caffeine extracted from coffee beans. It is used in soda, energy drinks, medications and candies that have no natural caffeine content. And people wonder if synthetic caffeine is more dangerous than caffeine from natural sources. Scientists say there is no difference between the two.