How much caffeine in a cup of coffee?
Brewed: 107.5 milligrams
Decaf Brewed: 5.6 milligrams
Decaf Instant: 2.5 milligrams
Drip: 145 milligrams
Espresso: 77 milligrams
Instant: 57 milligrams
It’s usually presumed that a regular cup of coffee contains 100mg of caffeine but it may range between 40 and 176 mg and the mean is closer to 85mg. There’s probably less caffeine in a cup of tea – one study showed a median of 27mg per cup with a range of 8 to 91 mg. An ounce of sweet chocolate may contain between 75 and 150mg of combined methylxanthines and a cup of chocolate or chocolate milk may contain 150-300mg.
The principal dietary sources of caffeine are overwhelmingly coffee and tea. Coffee accounts for some 54 per cent of ingested caffeine, while tea accounts for some 43 per cent. The remaining 3% consists mostly of caffeine ingested in the form of cocoa and chocolate products, various fabricated soft drinks and mate (a tea drunk especially in South America).
In Australia a 375ml can of Coca Cola and Pepsi Cola contains about 40mg of caffeine. Regulations allow a maximum of 145mg of caffeine per kilogram of cola-type drink (54.5mg per 375ml can). “Jolt” Cola – said to have “twice the caffeine” – actually contains the permissible legal limit of around 54mg per bottle.
In the USA, the permissible limit of caffeine in cola drinks and other carbonated beverages is 200mg per litre. The US drinks also have higher levels of sugar. Caffeine’s bitter taste acts as a flavouring agent to counteract the sweetness of the sugar.
Caffeine is absorbed rapidly into the bloodstream from the gastro-intestinal tract. It reaches maximum concentration within about an one hour. The blood distributes it throughout the body. It even manages to pass through the blood-brain barrier.
The half life of caffeine in the human body varies between 3 to 7 hours. Throughout the body it increases metabolic rate by around 10%. Females metabolise caffeine 20-30% more quickly than males. However, it will take women on “the pill” twice as long to metabolise caffeine as women who are ovulating.
Early experiments showed that low concentrations of caffeine may produce small decreases in heart rate, whereas higher concentrations may make the heart beat abnormally fast.
In the brain it constricts the cerebral blood vessels. If you’re used to drinking several cups of coffee a day but then you quit, those blood vessels will dilate, maybe enough to give you a powerful headache. It’s one of the best known withdrawal symptoms.
Many people know that caffeine is a strong diuretic – it makes you urinate more than usual. Apparently this is due to increasing the blood flow through the kidneys.
It can produce insomnia – delaying the onset of sleep and reducing total sleeping time. It has a small effect on respiration by increasing blood flow through the lungs and increasing the supply of air by relaxing bronchiolar and alveolar smooth muscle. That’s why it’s proving effective in treating the breathing problems of some prematurely born infants.
Some people experience tremors after drinking coffee and tea. That’s thought to be due to over-activation of the central nervous system.
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Tags: blood flow, caffeine, coffee, cup, cup of coffee, decaf, doctor, espresso, Health, How much, insomnia, instant, nervous system
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