Thursday December 1 2011
Could high-caffeine coffee be harming your health?
“Pregnant women are putting themselves and their unborn babies in danger by drinking coffee from high street chains,” reported the Daily Express. Other newspapers reported the wide range of caffeine levels in espresso shots from different coffee outlets.
Pregnant women who enjoy the occasional commercially prepared coffee should not worry unduly about these findings, although they should continue to be careful about how much caffeine they drink. Current advice from the UK Food Standards Agency (FSA) is that pregnant women should limit caffeine intake to 200mg a day.
The story comes from an analysis of the caffeine content of single shots of espresso from 20 high-street coffee shops in Glasgow. The amount of caffeine they contained varied considerably, from 322mg to 51mg a shot.
The authors say that normally quoted figures for caffeine levels in coffee, which they say are about 50mg a cup, are misleading. One single shot of a high-caffeine drink could place at risk people who are more susceptible to the toxic effects of coffee. These include pregnant women, women taking oral contraceptives, young children and people with liver disease, they warn.
The authors also highlight that many coffee outlets prepare other coffees, such as lattes and cappuccinos, from espresso shots. As they rightly conclude, coffee consumption in commercial outlets and caffeine content of other drinks need to be studied further, so that consumer information can be improved.
Caffeine is also found in other foods including tea, chocolate, some soft drinks, and some cold and flu remedies.
Where did the story come from?
The study was carried out by researchers from the University of Glasgow. No sources of external funding were reported in the paper. The study was published in the Royal Society of Chemistry’s journal, Food and Function.
The story was generally covered accurately in the media. The Daily Express’s claim that "pregnant women are putting themselves and their unborn babies at risk" was misleading as it implied the study found that pregnant women consumed excessive amounts of caffeine. The analysis was of caffeine levels in high-street coffee outlets. It did not look at caffeine intake among pregnant women or any other group.
What kind of research was this?
This was a chemical analysis of levels of caffeine in single-shot espresso coffees purchased from 20 different outlets. Researchers also looked at levels of another substance in these products called caffeoylquinic acid (CQA). They said that CQA has been demonstrated in the laboratory to have antioxidant properties, but there is limited evidence for any direct protective effects on human health.
They pointed out that consuming caffeine in excess can lead to unpleasant symptoms, although individual susceptibility varies. Certain groups, including pregnant women and young children, are more susceptible to the toxic effects of caffeine because their bodies process it more slowly.
The researchers also say that there is no published information on the caffeine content of the various types of commercially prepared coffees, despite the increasing number of coffee shops on the high street and in other settings, such as airports. The authors quote figures from a US review, published by the International Food Information Council Foundation, which suggest that a 28ml of espresso contains 30–50mg of caffeine.
What did the research involve?
The researchers bought single-shot espresso coffees from 20 different outlets in Glasgow’s west end. They measured the volume of each coffee serving, which ranged from 23ml to 70ml, before diluting it with methanol (alcohol) and freezing it. The diluted coffee samples were analysed using high-performance liquid chromatography (HPLC), a biochemical technique that can separate and identify individual components of a particular compound.
To explore a possible reason for any variations in the coffees’ caffeine and chemical content, they also carried out a similar analysis of six samples of ground espresso arabica coffee, prepared from beans subject to different roasting methods.
What were the basic results?
The analysis of caffeine levels in the 20 espresso shots found a six-fold variation in caffeine levels. The strongest coffee contained 322mg in one shot (from Patisserie Francoise), six times more than the lowest strength, which contained 51mg (from Starbucks). Three further products contained more than 200mg of caffeine and a further eight contained over 100mg (between 129mg and 173mg). The cup size ranged from 23ml to 70ml.
How did the researchers interpret the results?
The researchers concluded that the range of results in their snapshot of espresso coffees demonstrates that the normally quoted figures for caffeine content – about 50mg a cup – are misleading. Consumers at risk of caffeine toxicity, including pregnant women, children and those with liver disease, may unknowingly consume excessive caffeine from a single cup of espresso coffee.
They suggest that the large variability in caffeine content could be due to a number of factors, such as:
- the amount of coffee used to prepare the espresso
- differences between batches of coffee beans
- different procedures used to roast the beans (such as high-temperature short roast and low-temperature long roast)
- grinding conditions
- coffee-making process (such as the temperature of the water or steam, and ratio of coffee to water or steam)
They highlighted that since many coffee houses prepare larger-volume coffees, such as lattes and cappuccinos, by diluting a single or double shot of espresso, further study on these products is needed. New data are needed to provide labelling information "with attention to bean variety, preparation and barista methods".
This analysis provides a useful snapshot of the caffeine content in a range of espresso coffees bought on the high street. Although the study was carried out in only one city, its finding that there is a wide variation in caffeine content is likely to apply to coffee bought in other UK cafes. It found that the caffeine content of most products was higher than normally expected and it is possible that some coffee drinkers may unknowingly consume large amounts of caffeine. In some cases, a single serving may place people who are more susceptible to the toxic effects of caffeine at risk.
The researchers only looked at caffeine levels in espresso coffee, which may not be standard preference in the UK. Although they point out that other types of coffee drinks are based on espresso shots, further analysis of the caffeine content of the more popular, larger drinks is needed. The researchers carried out their analysis only once, without any replication, and the possibility of error in the chemical procedure used to analyse caffeine levels should be noted.
Pregnant women who enjoy the occasional commercially prepared coffee should not worry unduly about these findings, although they should take care with how much caffeine they consume. Current advice from the FSA is that pregnant women should limit caffeine intake to 200mg a day, due to concerns about potential associations with low birth weight and miscarriage. However, the risks from occasionally exceeding this recommended intake are thought to be low.
The FSA states that the average daily caffeine intake during pregnancy is already believed to be below 200mg. However, in light of the current study’s findings, further study investigation of the caffeine intake of pregnant women and other vulnerable groups would be valuable.
The researchers in this study say that a cup of coffee is assumed to contain 50mg of caffeine, but the FSA advises that a mug of instant coffee contains around 100mg caffeine, and a mug of filter coffee contains around 140mg of caffeine.
Consumers should also be aware that there is caffeine in other foods including tea, chocolate and some soft drinks. Caffeine is also found in some cold and flu remedies, and pregnant women in particular are advised to check with a pharmacist or midwife before they take any such remedies.
As the authors rightly conclude, their study indicates a need for more research into coffee consumption within commercial outlets and caffeine content of other drinks, so that consumer information can be improved.