We know that having a high level of cholesterol increases the incidence of heart disease and stroke and we avoid many high-fat foods as a result. But a new Scandinavian study makes a surprising find in that higher levels of cholesterol may be linked with an overall reduced risk of death.

The study published in the Scandinavian Journal of Healthcare sampled 120,000 adults in Denmark. Researchers found that people with higher rates of cholesterol (above the recommended 5.0 mark) were associated with reduced rates of cancer and many other illnesses.

The study, which looked at both good and “bad” (HDL and LDL) types of cholesterol, found that “higher lipoprotein [cholesterol] levels do not seem to be definitely harmful in the general population”.

Cholesterol is a much more complicated story than simply its relationship to heart disease. In light of the dietary trends to reduce cholesterol causing fats (many of which are essential to other functions) the study throws new light on how cholesterol levels relate to other aspects of health, not solely heart disease.

Cholesterol is a type of fat found in your blood which in excessive amounts clings to artery walls to form plaque. In addition to diet, cholesterol is produced in the liver and has many uses in the body including brain function. An excessive build-up of cholesterol plaque may block an artery, leading to heart attack or stroke.

Heart health
Cardiovascular disease is still the biggest cause of death in Ireland for both men and women. Happily, heart health is one of the health issues the public is widely aware of. One of the reasons for this is the flood of "cholesterol lowering" functional foods onto the market place which can reduce cholesterol levels and which tap into our fears about eating for a healthy heart. It's a heavily advertised market that is growing globally each year by $11.5 billion.

Prescription drugs such as statins are also used by tens of thousands of Irish people. Statins such as atorvastatin, (originally sold under the name Lipitor) are prescribed to lower cholesterol. The use of statins climbed 17 per cent globally between 2007 and 2012. They are prescribed in more than 214 million monthly prescriptions annually, according to data provided by IMS Health, a consulting firm that can track drug prescriptions at pharmacy level.

But what if you are unlikely to be predisposed to heart disease? Should you be buying yoghurt drinks that promise to make your heart healthier or taking cholesterol medicine? In those instances could lowering cholesterol be in fact bad for your health?

In Ireland and Europe generally, it is recommended that levels of cholesterol in the blood should not be above 5.0mmol/l ( about 190mg/dl). Anything above this is said to increase risk of heart disease or stroke.

In the Scandinavian study, researchers found that having higher-than-recommended levels of total cholesterol was associated with a reduced risk of death.

For instance, men aged between 60 and 70 with total cholesterol levels ranging from 5.00-5.99 mmol/l had a 32 per cent reduced risk of death than those with total cholesterol levels of less than 5.0.

For those with levels 6.0-7.99mmol/l, risk of death was 33 per cent lower. Even in individuals with what are considered very high levels of cholesterol – an 8.00mmol/l level and above, risk of death was no higher than it was for those with levels less than 5.0.

In the women surveyed, results were similar. In women aged 60-70, levels of 5.0-5.99 and 6.0-7.99 were associated with a 43 and 41 per cent reduced risk of death respectively.

'Weight of research'
For our understanding of high cholesterol as "bad", does this study suggest we should be wary of lowering cholesterol levels if we're not at risk of cardiac disease? Cecily Kelleher head of department of public health in UCD is wary of the argument. "There's such a volume of literature over decades linking high cholesterol with heart disease I would not think it's reasonable to caution anybody not to lower their cholesterol. It may be an interesting research question but the weight of research still points to high cholesterol being a risk".

In a related Scandinavian study, individuals found to have reduced cholesterol levels were more at risk of death from suicide, accidents and violence.

The research published in the Journal of Psychiatric Research showed a relationship between low or lowered cholesterol and death by suicide, violence or homicide. The researchers compared erratic and violent behaviour with the cholesterol measurements of nearly 80,000 men and women. They came to the conclusion that "low cholesterol is associated with increased subsequent criminal violence".

Several studies worldwide have tracked the same link but what’s unclear is exactly why low cholesterol is linked to negative mental health. Some suggest that low cholesterol impacts on normal brain function – possibly suppressing the production or availability of neurotransmitters such as serotonin.

In 2011, a wide-ranging Cochrane review of outcomes of patients on cholesterol-lowering medication stirred controversy when it recommended the need for further analysis on whether the health benefits of statins outweigh their disadvantages.

The review, lead by Dr Fiona Taylor from the London School of Hygiene and Tropical Medicine found that in high-risk populations – (those who had suffered a heart attack or stroke) the benefits from taking cholesterol-lowering medication are without question.

But in terms of lower-risk populations, the researchers said that “the effect of cholesterol-lowering medication is not large enough to justify the cost/effort and risk of adverse effects”.

One thousand people had to be treated with cholesterol-lowering medication for a year to prevent one death.

Cholesterol is a complicated story. As research continues on cholesterol levels and health outcomes outside the cardiac arena, it will be interesting to see whether advice on cholesterol lowering foods and medicines changes.