Some people with high levels of supposedly “good” cholesterol are at much greater risk of heart disease, a study suggests.
A bloodstream tussle takes place between “bad” cholesterol dumping fatty material in the arteries and good cholesterol taking it away.
But a Cambridge University study in the journal Science showed more good cholesterol was not always better.
It is thought the findings may help find new ways to protect the heart.
Eating olive oil, fish and nuts raises levels of high-density lipoprotein (HDL) – which is more commonly known as good cholesterol.
It is one of the things doctors test for when predicting your risk of a heart attack.
However, repeated trials that raise HDL with drugs have flopped, leading doctors to think something else is going on.
Some insight has come from studying rare mutations that leave people with high levels of good cholesterol.
Trials showed people with a mutation in a gene called SCARB1, which affects one-in-1,700 people, had very high levels of good cholesterol.
But they also had an 80% increased risk of heart disease – that is roughly the same increased risk as for smoking.
Further experiments showed the mutation was preventing HDL from dumping the fat it had collected in the liver for processing.
Prof Adam Butterworth, one of the researchers from the University of Cambridge, said: “This is significant because we had always believed that good cholesterol is associated with a lower risk of heart disease.
“This is one of the first studies to show that some people that have high levels of ‘good’ cholesterol actually have a higher risk of heart disease so it challenges our conventional wisdom about whether ‘good’ cholesterol is protecting people from heart disease or not.”
There have been huge efforts put into drugs to raise HDL in the hope they have the same impact as statins, which lower the bad cholesterol.
Prof Butterworth warned that drugs aimed simply at “trying to raise HDL may not be that useful”.
He said the size of different HDL particles or how good they are at transporting may be more important than the overall levels.
And that may be a more productive avenue of research.