Science - November 11, 2004

Researcher worked out how coffee raises cholesterol

Researchers have known for a long time that unfiltered coffee increases the concentration of fatty substances in the blood, and therefore increases the risk of heart and circulatory disease. But precisely how this occurred was not clear. Fortunately Mark Boekschoten decided to make it the subject of his PhD research.

The subject is not directly relevant to most Dutch people, who drink filtered coffee. Filtering results in a decrease in the substance that is responsible for increasing concentrations of ‘bad’ cholesterol LDL and unhealthy triglycerides in the blood. The substance in question is cafestol. ‘Percolated coffee and espresso contain relatively large amounts of cafestol,’ explains Boekschoten. ‘Filtered coffee contains hardly any at all.’ In Scandinavian countries, where boiled coffee was the custom, coffee contributed considerably to the incidence of heart and circulatory problems. When researchers such as Wageningen UR’s Martijn Katan discovered this effect, the Scandinavians started to change their coffee drinking habits.

‘Cafestol is a special substance,’ says Boekschoten. ‘It is found in food, but has the impact you would expect from a pharmacological substance. If we can work out how cafestol does this, we may be able to discover more substances that occur in food that have similar effects, or that have the opposite effect.’ Boekschoten does not exclude the possibility that a greater understanding of cafestol will lead to better medicines.

Boekschoten discovered that cafestol stimulates a receptor in the liver that keeps an eye on the concentration of bile acid. If the concentration rises, the bile acid stimulates the bile acid receptor more often. This sends a signal to the liver to produce less bile acid. In test tube studies Boekschoten observed that cafestol misleads the bile acid receptor into thinking that the manufacture of bile acid can be reduced, which has direct consequences for the cholesterol level. ‘The body uses bile to get rid of cholesterol. The liver makes bile acid from cholesterol and then eliminates the bile acid together with cholesterol through the digestive tract. If the production of bile acid declines the amount of cholesterol in the liver rises, eventually leading to a rise of cholesterol levels in the blood.’

Boekschoten worked together with the University of Leiden and Baylor College of Medicine in Houston, Texas. / WK

Mark Boekschoten received his PhD on 10 November. He was supervised by Professor Martijn Katan, personal chair in Human Nutrition.