Women with sophisticated language as young adults were less likely to suffer the symptoms of Alzheimer's disease in old age -- even when the characteristic brain lesions associated with Alzheimer's were present at death, researchers found.
The importance of these skills -- measured by the "idea density" in an essay they wrote early in adulthood -- held for women with intact cognition, regardless of whether a brain autopsy showed the hallmark plaques and tangles of Alzheimer's, Dr. Juan Troncoso of Johns Hopkins University and colleagues reported online in the journal Neurology.
The findings add to the evidence for a so-called "cognitive reserve" that protects against the effects of neurological disease, according to Dr. Robert Stern, a professor of neurology and Alzheimer's expert at Boston University, who was not involved in the study.
Language abilities -- like other measures of this reserve, such as years of education -- appear to be linked to "bigger and better brains," with more connections between neurons, he said. Rather than decreasing the likelihood that a person will develop Alzheimer's, it apparently staves off some clinical symptoms of the underlying disease, such as memory loss.
Exercising the mind early in life may help build a protective cognitive reserve, although studies like this cannot prove that these mental exercises are effective, added Dr. Samuel Gandy of Mount Sinai Alzheimer's Disease Research Center in New York.
"The notion of recommending language acquisition as a kind of mental exercise that might lower one's risk for Alzheimer's disease follows logically," Gandy said.
And even if it doesn't help in the end, language skills certainly can't hurt, he said.
Alzheimer's disease has puzzled researchers because the same degree of damage to the brain causes severe symptoms in some people, but not in others, Troncoso's group noted.
To determine what factors earlier in life might produce these differences, the researchers looked at a particularly Alzheimer's-vulnerable area of the brain during autopsies of 38 Roman Catholic nuns.
Autopsies showed that women with known Alzheimer's disease in this group had significant shrinkage of certain parts of the brain compared with those who had no symptoms or brain lesions.
But the women with asymptomatic Alzheimer's disease -- who showed no cognitive impairment before death but showed Alzheimer's disease-type brain lesions during an autopsy -- had markedly larger compartments of key cells in their brains compared with all the other groups of women.
These features may indicate that the neurons in the brains of these women repaired themselves or grew and made new connections to compensate for damage, the researchers said.
Across these groups, there were no differences in age at death, education level, or time from last cognitive evaluation to death that could explain the results.
However, language ability earlier in life did appear to correlate with whether these women showed Alzheimer's symptoms.
The researchers also analyzed essays that 14 of the women had written as they entered the convent five or six decades earlier.