They looked at rates of MI, fatal CHD and coronary revascularisation over 15 years in patients with genetic variations associated with lower LDL levels to disentangle the effects of LDL from other cardiovascular risk factors.
The study included an initial pool of 3,363 black and 9,524 white patients who were analysed to see if they had one of the genetic variants that leads to lower LDL.
The researchers identified 87 black patients with a variant associated with a 28 per cent lower mean LDL level, and 304 white patients with a variant associated with a 15 per cent lower average LDL level.
There was no difference between the genetic sub-groups and the rest in prevalence of other cardiovascular risk factors, with the exception of hypertension which was slightly less common in the genetic subgroups.
The researchers found that those with the gene associated with a 28 per cent lower LDL level had an 88 per cent reduction in CHD risk compared to those without the variant.
Those with the gene associated with a 15 per cent lower LDL level had a 50 per cent reduced CHD risk.
Lead researcher Dr Helen Hobbs, from the University of Texas Southwestern Medical Center in Dallas said: 'Low plasma levels of LDL had a dramatic effect on the incidence of coronary events over a 15-year period.'
Professor Mike Kirby, Letchworth GP and member of the Primary Care Cardiovascular Society, said: 'The contract target of 5mmol/l is just an audit standard.
We should go by the latest Joint British Societies guideline and aim for an LDL target of less than 2mmol/l.'
- N Engl J Med 2006;354:1,264-72