Takeaway coffees bought from popular High Street outlets contain up to three times more caffeine than those made at home, a study shows.
Consumers who drink just three or four cups a day may exceed the safe daily limit of the stimulant of 400 mg, the researchers warned.
Tests of more than 200 coffees purchased from popular chains such as Starbucks and Costa Coffee revealed that Americans had the highest levels of caffeine, averaging around 140mg per drink.
Homemade coffees made with one teaspoon per person had the lowest levels: around 23 mg.
Caffeine is a stimulant that can cause insomnia, nausea, tachycardia and headaches when consumed in excess.
Takeaway coffees bought from popular High Street outlets contain up to three times more caffeine than those made at home, study shows (file image)
The findings, published in the journal Nutrients, come just days after another team of scientists from Zydus Medical College and Hospital in India found that drinking more than 400 mg of caffeine a day is linked to higher blood pressure, a major risk factor for heart attacks and strokes.
Caffeine is believed to be the most widely used stimulant in the world.
Millions of people rely on it to start their day and shake off the morning sluggishness.
But the NHS recommends limiting daily consumption to 400mg due to the potentially dangerous side effects of excessive consumption.
For pregnant women, the limit is only 200 mg.
But scientists at the National Institute of Public Health in Warsaw, Poland, set out to analyse caffeine levels in takeaway coffees after becoming concerned that many consumers might be drinking too much.
Tests of more than 200 coffees purchased from popular chains such as Starbucks and Costa Coffee revealed that Americans had the highest levels of caffeine, averaging around 140mg per drink (file image)
They analyzed samples of espresso, cappuccino, latte and Americano from Starbucks and Costa Coffee, as well as from McDonald’s branches, gas stations, grocery stores and bakeries.
They found a wide variation in caffeine content: some had just 12.8 mg per serving, others had more than 300 mg.
Researchers found that, on average, it took just two to three American coffees to exceed the daily caffeine limit.
They said store-bought coffees tend to be served in much larger quantities than those drunk at home, increasing caffeine intake.
The strength of the coffee bean was also a factor.
Research suggests that British consumers are now spending more money than ever on takeaway coffee – an average of £530 per person per year.
In a report on their findings, the researchers called for coffee lovers to be given more practical information about caffeine content.
They said: ‘High caffeine consumption is not harmless to health: it can cause muscle tremors, insomnia, stomach upset and tachycardia (rapid heart rate).
We found that coffees served in franchises had significantly higher caffeine levels than those prepared at home.
‘More practical guidance would be recommended to avoid regular intake of high doses of the stimulant.’