We analyse data for 116,000 subjects from the Copenhagen City Heart Study and the Copenhagen General Population Study, in combination with mortality data from the Danish Civil Registration System. They have followed the subjects for an average of 6 years, and based the study on just over 10,500 deaths. The researchers were able to calculate the mortality rate based on these deaths and medical information on the subjects. The results showed that men with extremely high HDL levels in the blood had a 106 per cent higher mortality rate than men with a normal HDL level. Among women, those with extremely high levels of HDL had a 68 per cent higher mortality rate than the normal group. Men in the next group, with very high levels, also had a 36 per cent higher mortality rate.