Low IQ Linked to Dementia
Children with low IQs have more of a tendency to develop vascular dementia later in life than do those children with high IQs. This is according to a report published in the June 25, 2008 online issue of Neurology. Vascular dementia is the most common form of dementia after Alzheimer's disease and occurs when blood flow to the brain is impaired.
The study began by examining the results of mental ability tests the 173 Scottish participants had taken at the age of 11, in 1932, decades before they developed dementia. A control group of the same age and gender had their IQ test results examined for comparison. In yet another control group, researchers used cases where the fathers of the families of the participants had been employed in similar occupations.
While those participants in the vascular dementia group had a 40% increase of having low test scores as children, the difference was not seen in those study participants who did not develop dementia or who had developed Alzheimer's disease. Study author John M. Starr, FRCPEd, of the University of Edinburgh, stated, "There is something about your mental ability that adds further to your risk of vascular dementia."
Starr believes that the results of the study prove the importance of reducing vascular risk factors such as high blood pressure, high cholesterol, and smoking which may lead to strokes and the development of dementia.
The finding that low childhood IQ serves as a risk factor for dementia that is vascular in nature tends to disprove the "cognitive reserve" theory. Cognitive reserve theory holds that higher IQ and levels of education act as a buffer against the encroachment of dementia in the brain, thus allowing those with the largest cognitive reserve to remain symptom-free for the longest period of time, though the disease may already be affecting their brains.
This has implications for the study of Alzheimer's disease as well, since there appears to be no correlation between higher IQ and level of education in the timing of the development of Alzheimer's symptoms. In other words, higher levels of intelligence and education appear not to have any role in delaying the effects of Alzheimer's disease, thus disproving the cognitive reserve theory.
Researchers don't yet know the role IQ plays in the lead-in to vascular dementia; though Starr hypothesizes that mental ability may be an indication of how well the brain handles jobs such as controlling blood pressure. Starr comments, "It may be that IQ is a measure of system integrity."
Starr explains that he believes there is a possibility that the IQ is a reflection of how the brain handles vascular issues.