What is Cholesterol?
Cholesterol is a fatty substance that is found in our blood and cells, and can be transported in the bloodstream. Cholesterol levels can be measured by a doctor. We make cholesterol naturally, and it can also be found in certain foods.
Studies investigating the relationship between cholesterol and dementia look at many different ways that they might be linked. Evidence suggests that there is a relationship between having high cholesterol levels in the blood in mid-life, and going on to develop dementia.
People that have high cholesterol levels in the blood often have other factors associated with dementia risk such as high blood pressure and diabetes, so separating these factors is complex. The role that cholesterol in the brain plays in the development of dementia is also being investigated, and there are lots of avenues for this research to take. Evidence around the benefits of medications such as statins to reduce the risk of dementia is less clear; more research is needed.
Cholesterol levels and dementia risk
An observational study is one that looks at large numbers of people over time and tries to find patterns and relationships between different factors (in this case, cholesterol levels and dementia). These studies can be very helpful for our understanding of things that change the risk of certain conditions, and they have been very helpful in finding things that may affect the risk of developing dementia.
Observational studies analysing a link between high cholesterol levels and development of dementia have mixed findings. A review that looked at 25 of these studies suggests that higher cholesterol in mid-life is associated with an increased risk of developing the condition.
Understanding cholesterol in the brain
Researchers are also interested in cholesterol in the brain, as this substance and the way that it is processed are very important for the health of brain cells, and may be affected in dementia. For example, one of the common genes that increase the risk of late-onset Alzheimer's disease – APOE4 – plays a role in the processing and use of cholesterol and other fats. Understanding any differences may lead to clues about changes in the brain that cause dementia, and things that we could tackle with treatments.
Changes with cholesterol processing in the brain may not be related to the levels of cholesterol in the blood. More research is needed to better understand this relationship and what it can tell us.
The picture concerning statins is complex. In the past there have been concerns that in the short-term statins might cause memory-loss and confusion, which has been widely reported in the media, but more recent studies have generally not found this link.
Many people take statins to reduce their risk of heart attacks and strokes, and there have been many observational studies that have looked to see if this appears to alter the risk of dementia.
A meta-analysis is a study that looks at lots of previous studies and analyses all of the data together to increase the number of people studied and to look at the information in a consistent way. A meta-analysis looking at observational studies investigating statins and the risk of dementia looked at data from 11 studies, involving over 23,000 participants, who had been taking statins for between 3 and nearly 25 years on average. When all of the data was analysed together, the researchers found that those people taking statins had a 29 per cent reduced risk of developing dementia.