Previous studies, which have not examined twins with dementia and their healthy siblings, have shown that dementia and Alzheimer's disease occur more frequently among people who have low levels of education.
Cognitive reserve is thought to be a measure of brain capacity.
What may happen is that early in life, genetic and environmental factors combine to influence reasoning ability, or cognition, explained Gatz. So, cognitive reserve may be enhanced or reduced in different people. Furthermore, the rate at which cognitive reserve may decline over time may vary from person to person. The scientists studied 129 pairs of Swedish twins in which one twin in each pair had dementia. They compared these twins with data from 249 other twins with dementia and 498 healthy twins.