Taking statins could dramatically reduce the risk of dementia, even in those who already have low cholesterol, a major study has found.

The pill is one of the most commonly-prescribed drugs in the UK, with around seven to eight million people taking them to ward off heart attack and stroke.

Researchers now believe that the medication could reduce levels of harmful cholesterol in the brain — which they say could protect against types of dementia, including the most common, Alzheimer's.

The South Korean scientists found that those with naturally low levels of LDL cholesterol—often referred to as the 'bad' type—who weren't on medication were  less likely to develop dementia, compared to those with higher levels.

But they also discovered the risk of dementia reduced further among people who already had low levels of cholesterol and were taking statins compared to those who were not, suggesting the drugs provide 'additional protective effects'. 

It has long been thought that Alzheimer'sdisease, the most common form of dementia, is caused by the accumulation of toxic proteins in the brain. 

But experts behind the new study said their findings could change the way doctors think about the disease. 

'There is clearly more to the story of Alzheimer's than we first thought,' said Dr Francesco Tamagnini, a neurophysiologist at the University of Reading.

'Alzheimer's disease appears [that it] may be a complication caused by the accumulation of LDL [cholesterol] in the brain.'

Cholesterol is a fatty substance that naturally exists in blood vessels.

However, if levels of the harmful type — called LDL — become too high, it can clog up the arteries that supply the body's tissues with blood, increasing the risk of heart attacks and stroke.  

This can result from a number of reasons, including a genetic predisposition, a high fat diet and obesity. 

Another type of cholesterol, HDL, is often considered the 'good type' as it helps clear LDL away from the arteries and out of the body.

A level of HDL below 4mmol/L (millimoles per litre) is considered healthy.

The new study analysed the health records of 570,000 South Koreans, and found those who had levels of LDL cholesterol below 1.8 mmol/L were 28 per cent less likely to develop Alzheimer's disease, compared to those with twice as much LDL.

Those in the low cholesterol group who took statins were even less likely to develop the disorder, reducing their risk by a further 12 per cent.

The authors said their findings 'underscore the crucial role of managing LDL in lowering dementia risk', adding that statins could be used to improve cognitive function. 

The medicine lowers cholesterol by interfering with an enzyme in the liver that's crucial for making the fatty substance.

Some experts, however, have urged caution over the findings.

Dr Julia Dudley, Head of Research at Alzheimer's Research UK said: 'Dementia risk is complex and influenced by many factors.

'Without a detailed picture of what's going on in the brain, we do not know if there is a direct link between lower cholesterol and reduced dementia risk. 

'Clinical trials will be key to understand what effects statins might be having on disease processes in the brain.

'In the meantime, keeping our hearts healthy remains one of the most effective ways we can protect our brain health. 

'If you have any concerns about your cholesterol levels, you should speak to your GP.'

It is well known that high cholesterol is a risk factor for vascular dementia — a type of the disease caused by several mini strokes.

There are currently around 982,000 people with dementia in the UK. 

This number is expected to rise to 1.4 million by 2040.

Alzheimer's affects around six in 10 people with dementia.

Memory problems, thinking and reasoning difficulties and language problems are common early symptoms of the condition, which then worsen over time.

Previous studies have estimated that around 40 per cent of all dementia cases could be prevented with lifestyle changes.

This includes healthier diets, increased exercise, drinking less alcohol, preventing head injury and using hearing aids.  

Daily Mail