Summary

Although lower levels of high density lipoprotein (HDL) have been associated with heart disease, it is still not known whether it is a causal relationship or not. Danish researchers have drawn on some key heart research studies to show that people with low HDL for genetic reasons do not have an increased risk of heart disease. Therefore, low HDL alone is not likely to be an independent risk factor.

Introduction

Research shows that a low level of high-density lipoprotein (HDL, or 'bad') cholesterol is linked to an increased risk of heart disease. Therefore, when you have a cholesterol test, you'll hope for an acceptable HDL level and may turn to dietary changes to increase it. But did you know that researchers remain unsure as to whether HDL cholesterol really contributes, on its own, to heart disease risk? It may be that levels of triglycerides are more important and that they, in some way, decrease HDL - but the latter might not, on its own, be a risk factor. Scientists in Denmark set out to study the role of HDL with a group of patients who had a genetic disorder that gave them lifelong low HDL, even though the rest of their cholesterol profile is normal. If they had an elevated risk of heart disease, then low HDL is implicated - if not, then it is a distraction from the true issues.

What was done

Three separate heart studies were used - the Copenhagen City Heart Study, the Copenhagen General Population Study and the Copenhagen Ischemic Heart Disease Study. The researchers carried out DNA testing for people carrying mutations in a gene called ABCA1 which gave them low HDL levels. They checked all participants' HDL levels, their total cholesterol profile, and cases of heart disease.

What was found

Individuals with low HDL because of a mutation in ABCA1 did not have an increased risk of heart disease, so long as the rest of their cholesterol profile was normal.

What this study means

Lowered HDL only poses a risk of heart disease if it occurs with high triglycerides and higher levels of a component called atherogenic remnant lipoproteins. This study teaches us something important how cholesterol profiles should be measured and interpreted - gather as much information as possible and, if someone has low HDL, do not jump to conclusions over heart disease risk.