The report identifies two treatable factors that can lower the risk of dementia

YOUUntreated vision loss and high LDL cholesterol have been added as two new potentially modifiable risk factors for dementia in a report released Wednesday by the Lancet Commission.

These new additions join twelve other risk factors outlined by the committee, based at University College London, in previous reports on prevention, intervention and care for dementia in 2017 and 2020. The other risk factors are lack of education, high blood pressure, physical inactivity, diabetes, social isolation, excessive alcohol consumption, air pollution, smoking, obesity, traumatic brain injury and depression.

The committee’s latest findings suggest more ways to prevent dementia than previously known, said Gill Livingston, professor of psychiatry at University College London and co-author of the report.

“Many surveys have asked people aged 50 and over what diseases they are most concerned about, and dementia often comes up as the highest,” says Livingston. “And yet there’s a lot we can do to change the scale and make it less likely.”

Preventable vision loss and blindness affect an estimated 12.6% of adults aged 50 and over. By conducting a meta-analysis of 14 cohort studies, the committee found a 47% increase in the risk of dementia in adults with untreated vision loss. In another meta-analysis, cataracts and diabetic retinopathy had significant associations with dementia risk.

Follow-up studies in the US found that those who had cataract extractions had significantly reduced their risk of dementia – a 29% reduction – in contrast to those who had not had cataract extractions. Cataracts are characterized by the lens of the eye becoming cloudy, resulting in blurred vision. They can develop with aging and other conditions that cause proteins in the lens to break down and clump together.

Livingston said the role of vision loss as a risk factor for dementia can be compared to hearing loss, which was identified as a risk factor in an earlier report.

“One of the ways that both vision and hearing work is in terms of cognitive stimulation,” Livingston said. “People with hearing loss have a reduction in the volume of the temporal lobe.”

Maya Koronyo-Hamaoui, professor of neurosurgery at Cedars-Sinai Medical Center, said the retina is an important aspect of the dementia link. It is the only central nervous system tissue connected directly to the brain and not shielded by bone, allowing high-resolution non-invasive imaging.

“When we see retinal damage in our cohorts, there is almost always the same degree of damage in the brain,” Koronyo-Hamaoui said of her own research.

Molecular changes in the retina affect processes such as the circadian rhythm – responsible for regulating the sleep-wake cycle – and vision, which Koronyo-Hamaoui thinks could potentially reflect damage in the brain.

There is a social aspect of vision loss that plays a role in dementia risk, Livingston said.

“People who suffer these losses go out less, see fewer people and are much more likely to become socially isolated,” Livingston said. The report notes that vision loss tends to go untreated in low- and middle-income countries.

Higher LDL cholesterol – also known as “bad” cholesterol – was also associated with a higher incidence of dementia, the report’s authors found. High total cholesterol and low HDL were also found to be risk factors for dementia in an analysis of 27 studies. LDL is the type of cholesterol responsible for building up and clogging blood vessels, while HDL removes LDL from the bloodstream and returns it to the liver.

The committee said that individuals with high LDL, especially in middle age, ages 18 to 65, are at the highest risk for dementia.

What’s behind the link between high cholesterol and dementia risk? “Excess brain cholesterol is associated with people having higher amyloid levels in their brains and also with an increased risk of stroke,” Livingston explains. Buildup of the sticky protein amyloid is associated with Alzheimer’s disease, while an increased risk of stroke is associated with vascular dementia.

Erin Ferguson, a Ph.D. student and researcher in the department of epidemiology and biostatistics at the University of California, San Francisco, described the study as “very exciting work” because of the prevalence of high cholesterol and statin use in older adults. But she said the current evidence citing LDL as a risk factor is variable, based on what she has seen in her research at Kaiser Permanente on vascular comorbidities of dementia.

“Even looking at the 55 to 65 age group in this cohort, I can’t see a link between high LDL cholesterol and dementia risk,” Ferguson said of her own study cohort. “I’m a little surprised that LDL is the main cholesterol mentioned, when there is a lot of other evidence showing that HDL may play a factor.” She added that triglycerides, a type of fat that circulates in the blood and stores energy, may also play a role in preventing dementia.

Controlling cholesterol levels, such as lowering LDL, also reduces the risk of cardiovascular events such as stroke and heart attack, Ferguson noted. These events are in turn risk factors for dementia, namely vascular dementia.

There are several ways to maintain normal cholesterol levels to reduce the risk of dementia. According to Ferguson, statins are the best choice for older adults. For younger adults, she suggests exercise and diet to control LDL levels.

This story has been corrected to reflect that the retina is the only central nervous tissue that is both connected to the brain and not shielded by bone.