London - Pregnant women could unwittingly be putting the health of their unborn baby at risk by drinking coffee from high street cafes, researchers warn.
An analysis of espressos from 20 coffee shops uncovered huge variations in the amount of caffeine they contain - with the strongest having more than six times as much as the weakest.
Worryingly, the strongest example contained more than 50 percent more caffeine in a single cup than a pregnant woman is advised to take over the course of an entire day.
Fears about birth defects, miscarriage and premature delivery mean that pregnant women are advised to limit themselves to 200mg of caffeine a day. This is usually the equivalent of four cups of strong coffee, expected to contain 50mg of caffeine each.
But only one of the 20 coffees studied - the one from Starbucks - contained around this amount. All of the others were stronger.
Four had more than 200mg in a single cup, with the strongest having more than 300mg, the Royal Society of Chemistry journal Food and Function reports.
Researchers from Glasgow University bought single-shot espressos from 20 coffee shops in the city and measured their caffeine content.
The Starbucks espresso was the weakest, with 51mg of caffeine. In contrast, espresso from Costa Coffee had more than three times as much caffeine, with a reading of 157mg. At the top of the table was the espresso from Patisserie Francoise in the city’s West End - with 322mg of caffeine.
Repeating the experiment several times did not change the figures.
Researcher Alan Crozier said caffeine, which crosses the placenta to the unborn baby, usually takes five hours to break down in the body to half its previous level.
But the process can take up to 30 hours in certain groups, including children, liver disease sufferers and pregnant women. An unborn baby’s liver will struggle to break down caffeine, with potential long-term consequences. Even taking the Pill can hamper processing of caffeine.
Dr Crozier, a senior research fellow at Glasgow University’s school of medicine, said: “The levels of caffeine per serving varied more than six-fold. At the low level, a pregnant woman might safely drink four cups per day without significantly exceeding the recommended intake.
“At the higher end of the scale, even one cup of espresso will be well in excess of the advised limit.
“There is clearly a problem. People at risk could unwittingly ingest far more caffeine than they would ever dream of.”
Dr Crozier said the type of bean, the roasting process, grinding conditions and the coffee-making technique can all affect caffeine content, as well as the actual amount of coffee used.
He called for current guidelines on caffeine, from the Food Standards Agency, to be tightened and stricter monitoring of caffeine content.
A study of other coffees such as lattes and cappuccinos is also warranted, he said, as they are often made from an even stronger espresso base. He added: “There is every possibility this applies to all coffee shop coffees and not just espresso and not just in Glasgow.”
A spokesman for Starbucks said: “It is nothing new that caffeine is bad for pregnant women. We offer decaffeinated espressos in our stores. The quantity of caffeine doesn’t necessarily mean the coffee tastes weak.”
Patisserie Francoise was unable to comment. - Daily Mail