Vision loss and high cholesterol recognised as dementia risk factors

A major review has identified vision loss and high cholesterol as two new risk factors for dementia. It claims that eliminating these factors, along with 12 previously recognised ones, may prevent nearly half of dementia cases worldwide. But some of these factors are hard to eliminate, and genetics and old age are still the biggest risk factors for developing the condition.

“Dementia might be one of the most important health threats facing the population,” says Gill Livingston at University College London. “So, it’s incredibly important that there is a possibility that we can change this and have significantly fewer people with [this] illness.”

A 2020 iteration of the review identified 12 potentially modifiable risk factors for dementia: hearing loss, depression, smoking, high blood pressure, heavy alcohol consumption, obesity, air pollution, traumatic brain injury, diabetes, social isolation, physical inactivity and a lack of education.

Livingston and 26 other dementia experts from across the globe have now updated this list according to the latest evidence, keeping these 12 risk factors while adding two new ones: high levels of low-density lipoprotein (LDL) “bad” cholesterol below the age of 65 and untreated vision loss later in life.

The researchers included high LDL cholesterol based on multiple new findings. One was an analysis of 17 studies that followed nearly 1.2 million UK participants younger than 65 years old for more than a year.

It showed that each 1 millimole per litre (mmol/L) increase in LDL cholesterol was associated with an 8 per cent rise in dementia frequency. Another similarly sized study found that high LDL cholesterol – greater than 3 mmol/L – was linked with a 33 per cent greater risk of dementia, on average. The risk was most evident in people who had high LDL cholesterol during midlife. “So the duration makes quite a difference,” says Livingston.

The researchers suggest the association may be due to excess cholesterol in the brain raising the likelihood of stroke, which can cause dementia. Cholesterol has also been linked to an accumulation of plaques of beta-amyloid protein in the brain, which are involved in Alzheimer’s disease.

Untreated vision loss was included as a risk factor after an analysis of 14 studies, made up of more than 6.2 million older adults who were cognitively healthy at the start, linked it to a 47 per cent greater risk of developing dementia up to 14.5 years later. A separate analysis showed that the risk was mostly due to cataracts and the complications of diabetes. “We think that vision [loss] is a risk because it reduces cognitive stimulation,” says Livingston. Some research suggests that such stimulation bolsters the brain’s resilience to dementia.

The researchers then used models to estimate what percentage of dementia cases worldwide could be prevented if each of the 14 modifiable risk factors were eliminated. They found that hearing loss and high cholesterol had the greatest impact, each contributing to about 7 per cent of dementia cases, while obesity and excess alcohol consumption had the least influence, each contributing to 1 per cent of cases. Eliminating all factors would prevent an estimated 45 per cent of dementia cases, the team estimated.

However, just because these factors are associated with dementia doesn’t mean they cause the condition, says Dylan Williams, also at University College London, who wasn’t involved in the report. “Therefore, if we were to target them with interventions, they might not prevent the amount of disease we would expect them to.”

These estimates are only averages for the overall population and don’t capture risk on an individual level, says Williams. So, removing all of the factors from your life doesn’t necessarily halve your risk of dementia, which is mostly influenced by genetics and age. Eliminating many of these risk factors, such as air pollution and a lack of education, will also require public health interventions rather than changes by individuals, says Williams.

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