Takeaway coffees bought from popular High Street outlets contain up to three times as much caffeine as ground coffee brewed at home, a study shows.
Consumers who drink just three or four cups a day may exceed the safe daily limit for the stimulant of 400mg, researchers warned.
Tests on more than 200 coffees bought from popular chains such as Starbucks and Costa Coffee revealed Americanos had the highest caffeine levels — averaging around 140mg per drink.
Home-made coffees made with one teaspoon of ground coffee per person had the lowest levels — around 23mg.
Caffeine is a stimulant which can cause insomnia, nausea, rapid heart rate and headaches when drunk to excess.
Tests on more than 200 coffees bought from popular chains such as Starbucks and Costa Coffee revealed Americanos had the highest caffeine levels — averaging around 140mg per drink
Caffeine is a stimulant which can cause insomnia, nausea, rapid heart rate and headaches when drunk to excess
The findings, published in the journal Nutrients, come just days after a separate team of scientists from Zydus Medical College and Hospital in India found drinking more than 400mg of caffeine a day is linked to higher blood pressure — a major risk factor for heart attacks and strokes.
Caffeine is thought to be the most widely-used stimulant in the world.
Millions rely on it to kick-start their day and shake off the morning slumber.
But the NHS recommends limiting daily consumption to 400mg due to the potentially dangerous side-effects of over-consumption.
For pregnant women, the limit is just 200mg.
But scientists from the National Institute for Public Health in Warsaw, Poland, set out to test caffeine levels in takeaway coffees after becoming concerned that many consumers might be drinking too much.
They analysed samples of espresso, cappuccino, latte and Americanos from Starbucks and Costa Coffee, as well as branches of McDonald’s, petrol stations, grocery stores and bakeries.
They found a huge variation in caffeine content — some had just 12.8mg per serving, others had more than 300mg.
On average, researchers discovered, just two to three Americanos was often enough to exceed the daily caffeine limit.
They said shop-bought coffees tend to be served in much larger quantities than those drunk at home, adding to caffeine intake.
Coffee bean strength was also a factor.
Research suggests British consumers now spend more money than ever before on takeaway coffees — at an average £530 per person a year.
In a report on their findings, researchers called for coffee lovers to be given more practical information on caffeine content.
They said: ‘High caffeine intake is not harmless to health – it can cause muscle tremors, insomnia, upset stomachs and tachycardia (rapid heart rate).
‘We found coffees served in franchise shops had significantly higher caffeine levels than home-made ones.
‘It would be advisable to have more practical guidance to avoid the regular intake of high doses of the stimulant.’
