Drinking just three cups of coffee a day, purchased from retail chains, can exceed the safety limit for caffeine, experts say

Research shows that coffee you take with you from popular coffee shops contains up to three times more caffeine than ground coffee you brew at home.

Researchers warn that consumers who drink just three or four cups a day may exceed the safe daily limit of 400 mg for the stimulant.

Tests on more than 200 coffees from popular chains such as Starbucks and Costa Coffee found that Americanos had the highest caffeine levels, averaging around 140mg per drink.

Homemade coffee, made with one teaspoon of ground coffee per person, had the lowest levels: about 23 mg.

Caffeine is a stimulant that, when used in excess, can cause insomnia, nausea, rapid heart rate, and headaches.

Tests on more than 200 coffees purchased from popular chains such as Starbucks and Costa Coffee showed that Americanos had the highest caffeine levels – averaging around 140mg per drink

Caffeine is a stimulant that can cause insomnia, nausea, rapid heart rate, and headaches if consumed in excess

The findings, published in the journal Nutrients, came just days after a separate 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 considered the most widely used stimulant in the world.

Millions of people rely on it to start their day right and chase away morning sleep.

However, the NHS advises limiting daily consumption to 400mg due to the potentially dangerous side effects of overconsumption.

For pregnant women, the limit is only 200 mg.

Scientists at the National Institute of Public Health in Warsaw, Poland, wanted to test the caffeine content of coffee to go after becoming concerned that many consumers were drinking too much of it.

They analyzed samples of espresso, cappuccino, latte and Americanos from Starbucks and Costa Coffee, as well as from McDonald’s branches, gas stations, supermarkets and bakeries.

They found a huge variation in caffeine content, with some containing as little as 12.8 mg per serving, others over 300 mg.

Researchers found that an average of two to three Americanos was often enough to exceed the daily caffeine limit.

They said that store-bought coffee is often served in much larger quantities than coffee drunk at home, increasing caffeine intake.

The strength of the coffee beans also played a role.

Research shows 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 more practical information about caffeine content to be provided to coffee lovers.

They said: ‘High caffeine intake is not without risks to health – it can cause muscle tremors, insomnia, stomach upset and tachycardia (a fast heart rate).

‘We found that the coffee served in franchise stores contains significantly more caffeine than coffee brewed in-house.

‘It would be advisable to have more practical guidelines to avoid the regular intake of high doses of the stimulant.’