Vascular dementia occurs when the blood flow to the brain is impaired and is the most common type of dementia after Alzheimer's disease. A study of people in Scotland, who took an IQ test in 1932 when they were 11, has found that the people who went on to develop vascular dementia were 40% more likely to have low test scores when they were children than the people who did not develop dementia. However, there was not the same link between IQ and Alzheimer's disease. Risk factors for vascular dementia include high blood pressure, high cholesterol and smoking. The findings support the hypothesis that low childhood IQ acts as a risk factor for dementia through vascular risks rather than the "cognitive reserve" theory which says that greater IQ and education create a buffer against the effects of dementia in the brain allowing people with greater cognitive reserve to stay free of signs of dementia longer, even though the disease has started affecting their brains.
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