High cholesterol levels in middle age have been associated with an increased risk of developing dementia and Alzheimer’s disease more than a decade later, new research suggests.
High levels of low density lipoprotein (LDL) were linked to an increased risk of developing the conditions.
While elevated levels of total cholesterol were also associated with an increased risk, this link was weaker, suggesting that it is largely driven by LDL cholesterol, researchers say.
The study provides the strongest evidence to date on the relationship between blood cholesterol and dementia and Alzheimer’s disease. It was led by the London School of Hygiene & Tropical Medicine (LSHTM) with the University of Tsukuba, Japan and OXON Epidemiology, London and Madrid.
Supervisor Dr Nawab Qizilbash is a senior clinical epidemiologist at OXON Epidemiology and an honorary doctorate in pharmacoepidemiology at LSHTM.
He said: “While the link between LDL cholesterol and dementia and Alzheimer’s disease is modest and is found in people who are followed for more than 10 years from middle age, any adaptable risk factor is welcome for this enormous, growing and devastating disease. .
“Most of the known risk factors are difficult to change and convincing evidence that their change can prevent dementia when Alzheimer’s disease is scarce.
Similarly, long-term follow-up (more than 10 years) of randomized and non-randomized trials is needed to assess whether the benefits of LDL-cholesterol-lowering interventions – which greatly reduce coronary heart disease – increase the risk of dementia or Alzheimer’s disease. ”
Funded by Alzheimer’s UK, researchers used anonymous data from the UK Clinical Practice Research Database (CPRD) on more than 1.8 million UK adults.
They were all older than 40 and had taken a measurement of blood cholesterol between 1992 and 2009, with a follow-up period of up to 23 years or until diagnosis of dementia.
In what is believed to be the largest study of its kind, researchers were able to calculate the risks of subsequent dementias and Alzheimer’s disease for blood total cholesterol, LDL cholesterol, HDL cholesterol and triglycerides, adjusting for other factors.
Researchers are focusing on measures of blood cholesterol in middle age (under 65s) who have less illness.
A follow-up period of more than 10 years meant that they could prevent bias as a result of a long silent period when the pathology was present, but symptoms were clinically absent or unclear.
In the 953,635 people in the study who had an LDL cholesterol uptake, 2.3% (21,602) were diagnosed with dementia or Alzheimer’s disease.
Of the more than 1.8 million people who had an initial total cholesterol reading, nearly 50,000 (2.7%) had a follow-up diagnosis in the 23-year follow-up period, up to 2015.
The study found that the associations were weaker in people who had measured their blood cholesterol after the age of 65.
No consistent associations were observed for lipoprotein (HDL) cholesterol as high density triglycerides.
Lead author Dr Masao Iwagami, Assistant Professor at Tsukuba University and Honorary Associate Professor in Epidemiology and Population Health at LSHTM, said: “Our study contrasts in large all previous studies and delivers really accurate results.
“In people with cholesterol measured under 65 years of age, the risk of being diagnosed with dementia more than 10 years later was about 60% higher in those with LDL cholesterol levels above 200 mg / dL (5.17 mmol / L) compared to those with levels less than 100 mg / dL (2.6 mmol / L).
“The potency of this association is comparable to other adaptive risk factors such as alcohol consumption and greater than for blood pressure.”
The authors acknowledge limitations of the study including the lack of information on diet or physical activity, so it was not possible to assess the impact of these factors on blood cholesterol and how it could affect the observed associations.
The study is published in Lancet Healthy Longevity.