WASHINGTON, D.C. (July 09, 2000) - Results of a study of Swedish twins support previous research showing that education may protect against Alzheimer's disease and other forms of dementia, scientists reported at World Alzheimer's Congress 2000.
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.
"The theory is that cognitive reserve - greater levels of which might be marked by educational achievement - may act as a cushion against intellectual impairment," said lead researcher Margaret Gatz, Ph.D., professor of psychology at the University of Southern California, Los Angeles.
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.
"We hypothesized that low levels of education would be a significant risk factor when we compared twins with dementia to twins without dementia within the overall population of the study group," said Gatz. "But we also thought that comparing twins with dementia and their siblings who did not have dementia would show that education is not a significant risk factor, because the twins would have similar intellectual abilities determined by genetics."
In this study, low education was defined as six years or less of elementary school attendance. High education was anything beyond the sixth year of formal schooling.
The results show that when data is analyzed for the overall study population, low education is a significant risk factor for Alzheimer's disease and all other forms of dementia. Of the 249 cases of dementia, 216 (86.8 percent) fit the criteria for low education; of the 151 documented cases of Alzheimer's disease, 141 (90.4 percent) fit the criteria for low education. However, the effect of education was not significant when twins with dementia were matched against their healthy siblings. In 129 twin pairs, 86.8 percent of those with dementia had low education, compared to 87.6 percent of their healthy partners. This suggests that genetically determined abilities contribute to the protective affect of educational achievement in Alzheimer's disease not the attendance of educational activities. These findings were similar for identical and fraternal twins.
"Various complicating factors make it difficult to document whether level of education is related to dementia," says Bill Thies, Ph.D., vice president of medical and scientific affairs for the Alzheimer's Association (U.S.A.). "Education level is often associated with other possible influences, such as access to medical care, occupational and recreational activities, nutrition, income, alcohol intake and smoking. Because it is difficult to separate educational level from these factors, we should not point to education achievement alone as the only important variable."
Further analysis showed that twins who later became demented read fewer books, particularly as adults, compared to their non-demented siblings.
"We speculate that people with a higher cognitive reserve will have a lifelong difference in intellectual involvement and that this may be indicated by high levels of education, which may serve as an indirect marker of protection against dementia and Alzheimer's disease," said Gatz. "Thus, people who are well educated may have to experience greater mental declines before they show signs of dementia."
