June 2, 2010
Heavy Coffee Drinkers Build Up A Tolerance
Researchers say that using coffee for a pick-me-up may be pointless if you drink it all the time.
The researchers have discovered that people who drink a lot of caffeine develop a tolerance to its stimulatory effects.
They reported in the Neuropsychopharmacology journal that while caffeine can give people a buzz and raise alertness, the effect only works in those unused to the drink.
The experts based their assumptions on the results of a study carried out on 379 volunteers.
The scientists from the U.K. and Germany asked participants to abstain from the beverage for 16 hours.
Half of these participants were medium to heavy coffee drinkers that consumed at least one and up to six cups a day. Half were either non to low drinkers.
They gave half of the participants a 100mg espresso-size dose of caffeine. The other half was given a placebo shot containing no caffeine.
The medium to high group who received a placebo reported a decrease in alertness and an increase in headaches.
However, their post-caffeine levels of alertness were no higher than the non to low coffee consumers.
The investigators say this suggests caffeine only brings coffee drinkers back up to baseline or "normal."
However, if you are used to drinking lots of coffee you may well feel more drowsy if you stop.
The researchers say their findings back the idea that heavy consumers continue drinking lots of tea and coffee to avoid withdrawal symptoms.
"Although frequent consumers feel alerted by caffeine, especially by their morning tea, coffee or other caffeine-containing drink, evidence suggests that this is actually merely the reversal of the fatiguing effects of acute caffeine withdrawal," Professor Peter Rogers, of Bristol University, and colleagues told BBC News.
However, Dr Euan Paul of the British Coffee Association told BBC there was an "overwhelming wealth of evidence" showing that caffeine does increase alertness levels by acting as a stimulant on the central nervous system by prompting the release of adrenaline.
"This effect is not only found with subjects in a low state of alertness, like night time shift workers, or those who wake-up early in the morning, but is additionally found in subjects who already have a high state of alertness."
He recommended more research, adding: "Coffee when consumed in moderation, four to five cups per day, is safe and may confer certain health benefits, including contributing to your daily fluid intake."
But he told BBC that pregnant women should consider the advice given the Food Standards Agency and limit caffeine intake of 200mg per day from all sources.
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