Heart disease may be the number-one killer in the West, but we still don't fully understand its causes. While we accept that obesity, high cholesterol and smoking have an important part to play, up to half of all heart attack patients don't have any of these symptoms.
And what about psychosomatic issues, such as stress and depression? Nearly 30 years ago a landmark study determined that 'type A' people - those who are anxious about timekeeping, high-achievers and hostile - were twice as likely to develop a heart condition as a 'type B', who is easygoing and passive.
The trouble with this theory is that it has never been supported by any other trial since, even though it is one that has endured in popular culture.
So researchers from Northwestern University in Chicago decided to test the theory once again with a group of 3,308 young adults, aged from 18 to 30. They wanted to test if impatience, competitiveness, hostility, depression and anxiety in the group affected their chances of developing hypertension, or high blood pressure.
Interestingly, hostility was the only behavioural trait that could dramatically influence hypertension, the researchers found. Depression had a slight influence, while impatience had none at all.
(Source: Journal of the American Medical Association, 2003; 290: 2138-48).