Why some coffee drinker feel jittery and anxious after 4 cups of coffee and other coffee drinkers don’t?
About a decade ago, Ahmed El-Sohemy, a professor in the department of nutritional sciences at the University of Toronto, noticed the conflicting research on coffee and the wide variation in how people respond to it. Some people avoid it because just one cup makes them jittery and anxious. Others can drink four cups of coffee and barely keep their eyes open.
Dr. El-Sohemy suspected that the relationship between coffee and heart disease might also vary from one individual to the next. And he zeroed in on one gene in particular, CYP1A2, which controls an enzyme – also called CYP1A2 – that determines how quickly our bodies break down caffeine.
One variant of the gene causes the liver to metabolize caffeine very quickly. People who inherit two copies of the “fast” variant – one from each parent – are generally referred to as fast metabolizers. Their bodies metabolize caffeine about four times more quickly than people who inherit one or more copies of the slow variant of the gene. These people are called slow metabolizers.
What is the connection between heavy coffee drinking and heart disease?
With funding from the National Institutes of Health, Dr. El-Sohemy and his colleagues recruited 4,000 adults, including about 2,000 who had previously had a heart attack. Then they analyzed their genes and their coffee consumption. When they looked at the entire study population, they found that consuming four or more cups of coffee per day was associated with a 36 percent increased risk of a heart attack.
But when they split the subjects into two groups – fast and slow caffeine metabolizers – they found something striking: Heavy coffee consumption only seemed to be linked to a higher likelihood of heart attacks in the slow metabolizers.
The trend among fast metabolizers was quite the opposite. Those who drank one to three cups of coffee daily had a significantly reduced risk of heart attacks – suggesting that for them coffee was protective. Heavy and even moderate coffee drinkers were significantly more likely to have hypertension if they were slow metabolizers. But fast metabolizers saw their risk of hypertension fall as their coffee intake rose.