Not so good after all? Having high levels of HDL cholesterol ‘might raise your risk of dementia’ – but scientists find NO link with ‘bad’ type

Having high levels of so-called ‘good’ cholesterol could raise the risk of dementia, research suggests.

Scientists tracked rates of the memory-robbing condition among 185,000 people who were followed for nearly a decade.

Volunteers with the highest HDL cholesterol — considered the good kind — were 15 per cent more likely to get dementia than those with average readings. 

Meanwhile, participants with the lowest levels faced a 7 per cent heightened risk.

High-density lipoprotein cholesterol (HDL) is considered good because of the swathe of evidence showing it protects the heart.

Pictured: A cholesterol plaque in artery

It removes cholesterol from the arteries and carries it to the liver to be broken down and removed from the body — reducing the risk of heart attacks and strokes. 

But research has since started to challenge the traditional view that more is better when it comes to HDL levels. 

Some have shown too much circulating in the blood can contribute to inflammation. 

Others suggest that HDL clogs up the arteries when levels are too high, which can reduce blood flow to the brain and raise the risk of dementia.

The new Boston University study, which is merely observational and cannot prove a cause, found no such dementia link to levels of low-density lipoprotein (LDL) — the bad kind.

Academics acknowledged their findings were ‘unexpected’, saying they show there is a ‘complex’ link between HDL cholesterol and dementia.

Researchers recruited 184,367 participants aged 70, on average, at the start of the study who didn’t have dementia. 

Over two years, they filled out surveys on their behaviours and had their cholesterol measured regularly. Their health records were tracked for nine years, on average.

Findings published in the journal Neurology show 25,214 developed dementia over the course of the study. 

HDL cholesterol levels were 53.7milligrams per decilitre (mg/dL) on average. 

Levels above 40mg/dL for men and 50mg/dL for women are considered healthy. 

Participants with the highest levels were above 65md/dL. At the other end of the scale, lowest levels were grouped as 11 to 41mg/dL.

The results took into account other factors that could affect the risk of dementia, such as alcohol intake, blood pressure, cardiovascular disease and diabetes.

The team did not suggest any potential mechanism to explain their findings. 

Study author Professor Maria Glymour said: ‘The elevation in dementia risk with both high and low levels of HDL cholesterol was unexpected.

‘But these increases are small, and their clinical significance is uncertain.

‘In contrast, we found no association between LDL cholesterol and dementia risk in the overall study cohort.

‘Our results add to evidence that HDL cholesterol has similarly complex associations with dementia as with heart disease and cancer.’

The researchers noted that those who participated in the study were volunteers, meaning they may not be representative of the population. 

Cholesterol is a fatty, waxy substance found in the blood that is vital for bodily functions including digestion, making vitamin D and hormones.

However, too much can build up in the blood due to eating fatty food, not exercising enough, being overweight, smoking and drinking alcohol.

Having high LDL cholesterol doesn’t trigger any symptoms but can lead to blocked blood vessels and raise the risk of heart problems and strokes. 

Meanwhile, HDL cholesterol has been shown to protect against heart disease, with the NHS stating that levels above 18mg/dL for men and 21.6mg/dL for women are healthy.

Previous studies have suggested that having high cholesterol in middle age is linked to a higher risk of developing dementia.