Cholesterol has been questioned as a cause of heart disease in older people in a controversial new study.

A review of 19 studies involving 68,094 people, published in the BMJ Open journal, has found there is no association between what has traditionally been considered as "bad" cholesterol and the premature deaths of over 60-year-olds from cardiovascular disease.

Researchers found that 92% of the people in the study with a high cholesterol level lived longer.

Cholesterol is carried in the blood attached to proteins called lipoproteins. There are two main forms, LDL (low density lipoprotein) and HDL (high density lipoprotein). LDL cholesterol is often referred to as "bad cholesterol" because too much is unhealthy. HDL is often referred to as "good cholesterol" because it is protective.

Describing the findings as "robust" and "thoroughly reviewed," joint author Dr Malcolm Kendrick said: "These are the facts but they will be considered controversial."

Dr Kendrick, an intermediate care GP with the Central East Cheshire Trust, said: "What we found in our detailed systematic review was that older people with high LDL levels - the so-called 'bad' cholesterol - lived longer and had less heart disease."

The 17 international experts, who wrote the review, also found an inverse association with all of the deaths that occur in a population, regardless of the cause.

They conclude "our review provides the basis for more research about the cause of atherosclerosis (a hardening and narrowing of the arteries) and cardiovascular disease (CVD) and also for a re-evaluation of the guidelines for cardiovascular prevention, in particular because the benefits from statin treatment have been exaggerated."

It immediately prompted medical opponents to describe the results as "surprising", "completely the wrong conclusion" and part of a "disappointing unbalanced" paper.

Lead author Dr Uffe Ravnskov, former associate professor of renal medicine at Sweden's Lund University, said: "As elderly people with high LDL-cholesterol live the longest, there is no reason to lower it."

Co-author Professor Sherif Sultan, professor of vascular and endovascular surgery at the University of Ireland, said: "Lowering cholesterol with medications for primary cardiovascular prevention in those aged over 60 is a total waste of time and resources whereas altering your lifestyle is the single most important way to achieve a good quality of life.

"Cholesterol is one of the most vital molecules in the body and in the elderly prevents infection, intra-cerebral bleeds, cancer, premature cataracts, muscle pain and fatigue and thus must be protected and nourished."

Prof Colin Baigent, professor of epidemiology at Oxford University said the study had "serious weaknesses and, as a consequence, has reached completely the wrong conclusion."

Randomized trials of statin therapy which have studied substantial numbers of older people show " very clearly that people benefit just as much from reducing their cholesterol when they are in their 70s as when they are younger," he said.

Prof John Danesh, a British Heart Foundation professor at Cambridge University, felt the research had been based on "crude study methods" meaning that its statistical data regarding cholesterol levels and cardiovascular disease risk cannot be trusted.

Consultant cardiologist Dr Tim Chico, a reader in cardiovascular medicine at Sheffield University, said he would be more convinced by a randomised study where some patients have their cholesterol lowered using a drug (generally a statin) and others receive a placebo.

He said: "There have been several studies that tested whether higher cholesterol increases the risk of heart disease, by lowering cholesterol in elderly patients and observing whether this reduces their risk of heart disease. These have shown that lowering cholesterol using a drug does reduce the risk of heart disease in the elderly, and I find this more compelling than the data in the current study."

Professor Jeremy Pearson, the British Heart Foundation's associate medical director, noted there are many factors which determine health as people get older, making the impact of high cholesterol levels less easy to detect.

He said: " Evidence from large clinical trials demonstrates very clearly that lowering LDL cholesterol reduces our risk of death overall and from heart attacks and strokes, regardless of age.

"There is nothing in the current paper to support the authors' suggestions that the studies they reviewed cast doubt on the idea that LDL cholesterol is a major cause of heart disease or that guidelines on LDL reduction in the elderly need re-evaluating."