Large amounts of coffee are not good for the heart and blood vessels, but drinking just a couple of cups a day reduces the risk of cardiovascular disease. Epidemiologists have known this for a few years. But how moderate coffee intake protects the heart was not known. Until now.
The relationship between coffee and cardiovascular disease is represented by a J-curve. The graph below is from a Finnish study published in 2004. [J Nutr. 2004 Sep;134(9):2381-6.] It shows the relationship between coffee consumption and the number of cases of heart attacks in middle-aged men.
The researchers monitored two thousand men for five years.
As the graph shows, a coffee intake of six hundred millilitres per day has a protective effect. How this works is explained in a Swiss study published recently in the American Journal of Clinical Nutrition. In that study the researchers gave ten test subjects a cup of coffee early in the morning and then took blood samples. The Finns then exposed the ‘bad cholesterol’ LDL in the samples to copper ions. These oxidize LDL. Oxidized LDL is pretty bad for the blood vessels.
The researchers observed that, after drinking coffee, the LDL in the test subjects was protected against oxidation. At least, it took longer for the LDL to be oxidized.
Immediately after drinking the coffee nothing happens – but the LDL in a sample taken half an hour after drinking coffee oxidizes more slowly. And the LDL in a sample taken an hour after intake oxidizes even more slowly.
When the researchers analyzed the LDL they saw why. After drinking the coffee, phenols in the coffee like ferulic acid and the related chlorogenic acid embedded themselves in the LDL. These compounds prevent the LDL from being oxidized.
And it’s not only the phenols that are incorporated into LDL. “Incorporation into LDL was already shown for only a few other phenolic compounds”, the researchers write. They are referring to “quercetin and catechin, daidzein and genistein, rutin and quercetin, and tyrosol.” These substances are found in green tea, soya and olive oil.
By the way, the research was financed – you guessed it – by the food industry. In this case by institutes with scientific sounding names funded by the sector, such as the Institute for Scientific Information on Coffee and the Physiological Effects of Coffee Committee.
Coffee drinking induces incorporation of phenolic acids into LDL and increases the resistance of LDL to ex vivo oxidation in humans.
Epidemiologic and intervention studies indicate that both diet as a whole and single dietary components are involved in the risk of atherosclerosis. The resistance of LDL to oxidative modification is an ex vivo indicator of risk, which is modulated by dietary components. Coffee contains phenolic compounds with antioxidant activity. These molecules are found in plasma after the consumption of coffee, and it has been shown that, in vitro, they are able to decrease the susceptibility of LDL to oxidation.
The aim of this study was to evaluate the effect of coffee consumption on the redox status of LDL as modulated by the possible incorporation of phenolic acids into LDL.
Ten healthy volunteers, after an overnight fast, drank 200 mL filtered coffee. Blood was drawn before and 30 and 60 min after drinking. Changes in LDL redox status were evaluated by the measure of LDL resistance to oxidative modification and the concentration of LDL(-), a mildly modified, electronegative LDL subfraction. Chlorogenic and phenolic acids concentration in LDL were measured by electrochemical HPLC.
The resistance of LDL to oxidative modification increased significantly after coffee drinking, but the LDL(-) concentration did not increase. The concentration into LDL of conjugated forms of caffeic, p-coumaric, and ferulic acids increased significantly after coffee drinking.
Drinking 200 mL (1 cup) coffee induces an increase in the resistance of LDL to oxidative modification, probably as a result of the incorporation of coffee’s phenolic acids into LDL.
PMID: 17823423 [PubMed – indexed for MEDLINE]