It’s not called the silent killer for nothing. Without any outward signs or symptoms, cholesterol – a waxy, fatty substance in the blood – can slowly build up, clogging arteries and leading to potentially fatal heart attacks and strokes.
It is thought that as many as six in ten adults in the UK have abnormally high levels of alcohol, and most are completely unaware of it.
It is particularly worrying that prevalence has risen sharply since the pandemic, after decades of decline. This has been attributed to a fall in the number of people invited for NHS Health Checks, which measure cholesterol and are supposed to be given to everyone aged 40 to 74 every five years.
But decades of scientific research have shown that there is even more cause for alarm. High cholesterol – and in particular a type known as low-density lipoprotein (LDL) – is an integral part of the cascade of problems that eventually lead to dementia.
Studies that have followed millions of people for decades have found that every small increase in the amount of LDL circulating in the blood is associated with an eight percent increase in the risk of dementia in old age. And persistently high levels can increase the risk by 33 percent.
Interestingly, the risk was greatest in middle age, between the ages of 40 and 65. This suggests that high cholesterol at this stage can set in motion a chain of problems that can lead to dementia.
It’s undoubtedly a shocking development, but it also presents a huge opportunity to tackle heart disease and one of our most feared brain diseases simultaneously.
Doctors say it’s never too late to do something about your high cholesterol
Not only can high cholesterol levels be easily and cheaply diagnosed by your GP or with self-tests, there are also extremely effective ways to lower them.
Several best-evidence studies have shown that statins – drugs that lower cholesterol – can reduce the risk of dementia, particularly Alzheimer’s disease, by up to a third.
Even cutting out unhealthy foods high in saturated fats (which are linked to high cholesterol) can reduce your risk.
A Danish study, which followed people for an average of 58 years, found that people who did not adhere to healthy dietary guidelines were more likely to have high LDL cholesterol and develop certain types of dementia, compared with people who followed a balanced, healthy diet.
‘Simple lifestyle changes to lower your cholesterol can have a huge impact on brain function and could ultimately delay or even completely prevent dementia and heart disease in later life,’ said Dr Osman Shabir, an expert on the impact of cardiovascular disease on the brain at the University of Sheffield, working with Alzheimer’s Research UK and the British Heart Foundation.
“If your cholesterol is high, you can do something about it. Even if you’re in your 50s or 60s, you can change these risk factors. It’s never too late.”
The mechanism linking high cholesterol and vascular dementia, a form of the disease that occurs when blood flow to the brain is reduced, is well understood. As we age, blood cholesterol levels, which are produced primarily by the liver but are also linked to a high-fat diet, rise.
Doctors are generally most concerned about LDL levels: fat and protein globules that carry cholesterol from the liver into the bloodstream and are often called “bad” cholesterol because they can clog arteries.
The body also produces high-density lipoprotein (HDL), often called “good” cholesterol because it carries cholesterol away from the arteries to the liver, where it is broken down and excreted.
Over time, LDL can build up and harden the walls of your arteries, leading to clots. These can break down and damage the blood-brain barrier, a delicate layer of cells designed to protect the brain from clots and toxins.
‘This can allow blood clots to travel to the brain and cause strokes, reducing blood flow to parts of the brain and eventually leading to vascular dementia,’ said Dr Owen Peters of the UK Dementia Research Institute.
And the relationship between cholesterol and Alzheimer’s is more complicated.
Alzheimer’s develops differently than vascular dementia and is associated with the buildup in the brain of toxic plaques called amyloid and “tangles” of proteins called tau. Some studies have shown that heart disease, including high cholesterol in the body, triples the amount of amyloid in the brain.
Dr. Shabir says, “Brain cells can’t do their job of clearing amyloid properly. So you get more of it building up faster, which can increase the risk of Alzheimer’s.”
Research is also being conducted into the relationship between genetic risk factors for Alzheimer’s and cholesterol levels in the brain.
The brain makes its own supply of cholesterol, which is a key part of brain cell structure and communication between cells. But people who carry two copies of a gene called APOE4—who are eight times more likely to develop Alzheimer’s—have higher amounts of amyloid in their brains, as well as higher LDL cholesterol, Dr. Peters says.
About two percent of the population has two copies of this gene, which they inherit from their parents.
“It’s not clear whether this is related to cholesterol from the body crossing a ‘leaky’ blood-brain barrier, or to some other process happening in the brain,” he says. “The APOE4 gene is involved in cholesterol transport in the brain, but we don’t know how it all connects. The relationship is very complicated, but it seems clear that cholesterol plays a role in Alzheimer’s.”
People with another gene, APOE2, are more protected against Alzheimer’s and tend to have lower cholesterol levels, underscoring evidence that cholesterol seems to be important.
Be that as it may, research shows that prescribing statins in middle age can significantly reduce the risk of dementia.
These once-a-day pills that reduce the amount of LDL the liver produces can lower levels by as much as 50 percent. They also reduce the risk of clots forming.
An analysis found that people taking a statin had a 32 percent lower risk of Alzheimer’s disease and a 20 percent lower risk of vascular dementia, compared with people with untreated high cholesterol.
Some experts caution against this, as these studies are only observational and show a correlation over time. Moreover, doubts about the theory remain.
A review of the evidence by the respected Cochrane group of researchers found that statins given to people at risk of vascular disease did not prevent cognitive decline or dementia. However, the studies the team looked at gave statins to people later in life, when the damage caused by high cholesterol may have already set in motion the biological processes that lead to dementia. In other words, it may have been too late.
Despite the gaps in knowledge, experts agree that maintaining healthy cholesterol levels can only have benefits for overall well-being – whether it involves taking statins, changing your diet or becoming more active.
The NHS advises eating less fatty foods, especially high-fat foods such as butter, cheese, meat pies, fatty meats, cakes and biscuits.
Instead, eat more oily fish, such as mackerel and salmon, brown rice, wholegrain bread and pasta, nuts and seeds, and fruits and vegetables.
An analysis of the evidence found that diets high in tomatoes, flaxseeds, almonds, soy protein, avocados, and high-fiber or whole grain products caused “small to moderate” reductions in LDL. However, unfiltered coffee and sugar caused increases.
“Adopting heart-healthy habits can have a profound effect on heart health, but also on brain health,” says Ioanna Tzoulaki, professor of chronic disease epidemiology at Imperial College London. “That can include eating healthier, exercising more and taking statins, if needed, to lower cholesterol.”
The government needs to do more to ensure all adults get their NHS health check, according to Alzheimer’s Research UK (ARUK).
The 30-minute appointment, which should be offered every five years to everyone between the ages of 40 and 74, involves a series of tests to detect early signs of life-threatening diseases.
Patients typically have their height, weight and waist circumference measured, their blood pressure checked, and a finger-prick blood test done to determine their cholesterol.
The doctor will then explain to the patient the risk of developing a serious condition, such as heart disease, stroke or kidney disease.
However, data shows that only 56 per cent of men and 61 per cent of women take up the offer of an NHS Health Check. The number of people going for their check-up – similar to an MOT for the body – has also fallen over the past three decades. In 1998, 66 per cent of men and 67 per cent of women had the tests.
Following the findings of the Lancet Commission study, the Health Check cholesterol test could now also be an important tool to warn of the risk of developing dementia.
“It is vital that more people attend these important meetings,” said Samantha Benham-Hermetz, Director of ARUK.
‘It’s a double win, because keeping your cholesterol at healthy levels not only reduces your risk of dementia, but also diabetes and heart problems.’