Study details and key findings

For the study, researchers from University College London analyzed 14 prospective cohort studies that included 6.2 million older adults who were cognitively intact at baseline. Over a 14-year follow-up period, more than 171,800 of these adults developed dementia.

Aside from 12 previously identified risk factors for dementia, the researchers also identified two new risk factors. The previously identified factors include hearing loss, lower education, smoking, hypertension, obesity, physical inactivity, depression, diabetes, excessive alcohol use, air pollution, traumatic brain injury, and social isolation.

The first newly identified risk factor was vision loss. An estimated 12.6% of adults ages 50 and older experience avoidable vision loss and blindness. In a meta-analysis of the 14 cohort studies, researchers found that adults with untreated vision loss had a 47% increase in dementia risk.

Another meta-analysis found that cataracts and diabetic retinopathy also had significant associations with dementia risk. According to follow-up studies conducted in the United States, people who had cataract extract decreased their risk of dementia by 29%.

Gill Livingston, a professor of psychiatry at University College London and one the study's authors, said vision loss as a risk factor for dementia can be compared to hearing loss.

"One of the ways in which both vision and hearing act is in terms of cognitive stimulation," Livingston said. "People who have hearing loss have a reduction in the volume of the temporal lobe."

Livingston also noted that there is a social aspect of vision loss that could contribute to dementia risk. "People who have these losses go out less, see other people less, are much more likely to become socially isolated," he said.

The second newly identified risk factor was higher LDL cholesterol, which is also known as "bad" cholesterol. LDL cholesterol is responsible for buildup and blockage of arteries, while HDL cholesterol removes LDL from the bloodstream and brings it back to the liver.

According to the study, individuals between the ages of 18 and 65 with high LDL have the highest risk for dementia.

"Excess brain cholesterol is associated with people having higher amyloid within their brain and also with increased stroke risk," Livingston said. A buildup of amyloid is associated with Alzheimer's disease, while increased stroke risk is associated with vascular Alzheimer's.

Commentary

According to Joshua Ehrlich, an associate professor of ophthalmology and visual sciences at the Institute for Social Research at the University of Michigan, "[t]here is now overwhelming evidence that vision impairment in later life is associated with more rapid cognitive decline and an increased risk of dementia."

Ehrlich also noted that the association between untreated vision loss, dementia risk, and potential modification by treatment has clear care implications.

"Loss of vision impacts so many aspects of people's lives beyond just how they see the world and losing vision in later life is not a normal part of aging," he said. "Thus, when older adults experience vision loss, this should be a cause for concern and prompt an immediate referral to an eye care professional."

Esme Fuller-Thomson, director of the Institute for Life Course and Aging at the University of Toronto, agreed. "Addressing vision loss will certainly help people see better and function at a higher level and improve quality of life, and it seems probable that it might decrease dementia risk so it's a win-win," she said.

Separately, Erin Ferguson, a Ph.D. student and researcher in the department of epidemiology and biostatistics at the University of California, San Francisco, said that the research is "very exciting work" due to the prevalence of high cholesterol and statin use among older adults.

However, Ferguson noted that, based on her own research at Kaiser Permanente, the current evidence of LDL cholesterol as a dementia risk is variable. "Even looking at ages 55 to 65 in this cohort, I'm not able to see an association between high LDL cholesterol and dementia risk," Ferguson said about her own research cohort. "I'm a little surprised that LDL was the main cholesterol listed when there's a whole lot of other evidence showing that HDL may play a factor."

According to Ferguson, triglycerides, a type of fat that circulates in the bloodstream and helps store energy, could also help prevent dementia. Regulating levels of cholesterol, including lower LDL, will decrease the risk of cardiovascular events, like heart attack and stroke, which could then decrease the risk of dementia.

To maintain normal cholesterol levels, older adults can use statins. For younger adults, Ferguson suggests diet and exercise to keep LDL levels at a normal level. (Taylor, Becker's Hospital Review, 8/19; Rajeev, STAT, 7/31; Rudy, Fox News, 8/19; Brooks, Medscape, 8/15)

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