A coup of coffee increases the risk of a heart attack for people with a defect in the gene responsible for breaking down coffee. People with a normally-processing gene can drink as much coffee as they want, scientists say. Coffee is the most consumed drink in the world, $17 billion a year being spent only by Americans on this beverage; more than half of the adults begin their day with a hot cup of coffee. The present study tries to clarify why earlier studies have shown conflicting results about coffee's effects on people, by looking at genetic differences among coffee drinkers. Researchers from the University of Toronto in Canada compared 2,000 people who suffered a heart attack to 2,000 healthy people. After being interviewed about their coffee drinking habits, the gene that processes caffeine was tested for mutations. Results have shown that people with abnormal gene process caffeine up to 4 times more slowly that the ones with a normal gene, said Ahmed El-Sohemy, researcher involved in the study. Caffeine causes blood vessels to constrict, leading to an increase of the blood pressure. No commercial tests have been done on the CYP1A2 gene, even if scientists have been aware of its existence since the 1990s. Every person possesses two copies of the gene; the ones with mutations in one or both gene will break down caffeine slowly. Studies have also shown that a cup of coffee a day for people with the genetic defect does not increase the risk of a heart attack, but those who drank about 3 coups had a 36% higher risk for an attack; four or more coups increased the risk with 64%. Women with the mutated gene face a higher risk then men, the same being true for young people in comparison to older people. Coffee was discovered to reduce the risk of a heart attack with 22% for people with normal CYP1A2 genes.