When it comes to cholesterol, it’s usually sorted into the ‘good’ kind and the ‘bad’ kind based on their effects on heart health – but now a new study has shown that the ‘good’ type of cholesterol could have other health risks attached.

The latest research links an abundance of High-Density lipoprotein cholesterol (HDL-C) to a higher risk of dementia in older adults. For those above 75 years of age, the risk increases by 42 percent, the analysis showed.

The research, led by a team from Monash University, looked at data on 18,668 adults aged over 65 from Australia and the U.S.

Overall, for those diagnosed as having high HDL-C levels the risk of dementia increased by 27 percent on average, with individuals followed for an average of 6.3 years.

“This is the most comprehensive study to report high HDL-C and the risk of dementia in older people,” write the researchers in their published paper.

“Findings showed that high HDL-C was associated with dementia risk and that the risk increased with age.”

Most of the cholesterol in our bodies is the Low-Density lipoprotein (LDL) or ‘bad’ type, and if there’s a lot of it in the blood, it can clog up arteries, increasing the risk of heart disease and strokes. The main benefit of HDL-C is keeping LDL-C levels in-check.

A normal level of HDL-C in the blood is considered to be 40–50 milligrams per decilitre (or mg/dL) for men, and 50–60 mg/dL for women – roughly 40–60 parts per thousand. Almost 15 percent of the participants (2,709 people) had what was regarded as high HDL-C levels as the study started, which is 80 mg/dL or above.

The increase in risk is quite a jump, and the association remained significant when adjusted for factors such as age, sex, education, alcohol consumption, and daily exercise.

However, this doesn’t prove the cholesterol is causing the increase in dementia – only that there’s evidence of a link.

“While we know HDL cholesterol is important for cardiovascular health, this study suggests that we need further research to understand the role of very high HDL cholesterol in the context of brain health,” says epidemiologist Monira Hussain from Monash University.

The researchers didn’t dig into any possible biological mechanisms that could be connecting high HDL-C with dementia, which could be looked at in future studies. What we do know is that everything in our bodies is closely linked – including the heart and the brain.

Experts still aren’t sure exactly how dementia gets started, so discoveries of associations like this help guide research in the right direction. Further down the line, it could potentially aid in the development of preventative treatments or cures and in recognising who might develop dementia and who might not.

“It may be beneficial to consider very high HDL cholesterol levels in prediction algorithms for dementia risk,” says Hussain.

The research has been published in The Lancet Regional Health – Western Pacific.