Children who have lower IQs are more likely to develop a type of dementia as adults compared to children with high IQs, new research says.
In a study of more than 170 people in Scotland, English researchers found that subjects with vascular dementia were 40 per cent more likely to have had low IQ test scores as children than those who did not develop dementia.
Vascular dementia is the most common form of dementia after Alzheimer's disease. It occurs when blood flow to the brain is disrupted.
Because the findings did not translate to patients with Alzheimer's disease, the researchers believe that having a low IQ is linked to vascular dementia because it influences the development of vascular risk factors, such as smoking, high blood pressure and high cholesterol.
They had thought it was possible that a low IQ could indicate the brain is more vulnerable to vascular changes.
The study is published in the June 25 online edition of the journal Neurology, the medical journal of the American Academy of Neurology.
The researchers said that the findings will help doctors determine the best way to prevent dementia symptoms in their patients, by either reducing vascular risk factors or improving the brain's protective mechanisms.
Abstract:
Childhood cognitive ability and risk of late-onset Alzheimer and vascular dementia
Brian McGurn, MRCP, Ian J. Deary, PhD, John M. Starr, FRCPEd
Background: Risk factors for dementia can be divided into those that lead to pathologic insults and those that render the brain more vulnerable to such insults. Dementia prevention strategies need to be informed as to whether to prioritize reducing risk of pathology or to reduce the vulnerability of the brain to pathologic insult. Lower premorbid cognitive ability is associated with both increased vascular risk and reduced cognitive reserve, a measure of brain vulnerability. We investigated differential effects of premorbid cognitive ability on dementia subtypes to clarify which causal pathway was predominant.
Methods: A total of 297 cases of late onset dementia were identified from local case registers, born in 1921, and thus may have participated in the Scottish Mental Survey of 1932 (SMS1932). A total of 183 had mental ability scores identified in the SMS1932. A total of 173 of these were matched by birth records to one set of controls (controls1) by date of birth, sex, and district of birth registration. A further set of controls (controls2) was generated additionally matched on paternal occupation.
Results: Vascular dementia cases had significantly lower premorbid cognitive ability (OR 0.62, 95% CI 0.41-0.94, for every 10-point increase [0.7 SD] in mental ability score vs controls2), but there was no significant difference in the premorbid cognitive ability of Alzheimer disease cases (OR 1.02, 95% CI 0.82-1.28) vs controls2.
Conclusion: Lower premorbid cognitive ability is a risk factor for vascular dementia, but not Alzheimer disease. This suggests its effect acts mainly through vascular pathology rather than brain vulnerability.
