Researching the causes of dementia has been mostly focused on the brain, such as brain-cell death, plaque buildup in the brain, or lack of oxygen and nutrition delivery to brain cells.
So what does one of your five senses have to do with dementia?
Maybe everything, says a new study in the journal Aging and Mental Health.
This is because reduced function in one of your five senses seems to directly lead to dementia.
A research team led by the Medical Informatics Center at Peking University conducted a review of the available scientific literature to find out whether there is evidence for the idea that vision loss is a dementia risk.
They searched for studies published before 2020 in a wide range of medical journal databases and found 16 good-quality studies with 76,373 subjects over the age of 50 years. 11 of these studies ran over a long period, making it possible for the researchers to determine whether the vision loss or dementia happened first.
After crunching the numbers, they found that both subjectively and objectively diagnosed vision loss were risk factors for poor cognitive performance.
Here are the findings:
1. When vision loss was identified via subjective measures, the risk of a loss of cognition was 63% higher, versus 59% when the vision loss was diagnosed via objective measures.
2. People with vision loss at the beginning of the study were 137% more likely to have dementia at the beginning of the study.
3. Compared with the subjects with normal vision at the beginning of the study, those with vision loss were 44% more likely to develop dementia and 41% more likely to develop cognitive impairment in subsequent years.
So why on earth would visual impairment increase our chance of developing dementia?
The researchers offered some potential theories.
First, if there are brain processes that rely on vision and that vision is removed, those brain processes will obviously deteriorate. For example, parts of your brain process the information received from your eyes. If those parts of your brain suddenly have nothing to do, they might stop working and take down some other cognitive abilities that depend on them too.
Second, most people rely on their eyes for much of their cognitive stimulation. Think of reading, television viewing, drawing, and so on. If a loss in vision cuts their cognitive stimulation and they do not get the stimulation through some other methods, their brains will be less active and they will lose their cognitive abilities.
Third, people who rely on vision for most of their social interaction will become socially isolated, which previous research has linked with dementia.
This shows how important it is to get visual problems corrected as you age.