January 11, 2011
Having a larger head circumference, a sign of a bigger brain in young children, may lower the risk of Alzheimer’s in old age, a new study reports. The findings add to a growing body of evidence that the larger the brain and the richer the connection between brain cells, the less likely you may be to develop memory loss and thinking problems in old age.
“These results add weight to the theory of brain reserve, or the individual capacity to withstand changes in the brain,” said study author Robert Perneczky, M.D., of the Technical University of Munich in Germany.
The brain reserve theory holds that a large brain with robust connections can better withstand the ravages of Alzheimer’s disease. As brain cells die off from the accumulation of the plaques and tangles of Alzheimer’s, enough may remain to keep the brain working normally.
The findings highlight the importance of proper brain development early in life. Because brain size reaches most of its full measure by age 6, the authors note, measurements of head circumference mainly reflect brain development during the early childhood years. Dr. Perneczky said that while brain growth is determined in part by genetics, it is also influenced by nutrition in childhood. Infections and inflammations of the central nervous system as well as brain injuries can also impair brain growth.
“Improving prenatal and early life conditions could significantly increase brain reserve, which could have an impact on the risk of developing Alzheimer’s disease or the severity of symptoms of the disease,” he said.
For the study, which was published in the journal Neurology, 270 people with Alzheimer’s disease took tests of their memory and cognitive skills. They also had MRI scans of their brains to measure the amount of brain cell death. Brain size was determined by measuring the head’s circumference.
The study showed that a larger head size was associated with a greater performance on memory and thinking tests, even when there was an equivalent degree of brain cell death. Specifically, for every one percent of brain cell death, an additional centimeter of head size was associated with a six percent greater performance on the memory tests.
Larger brains may have more connections between them. Alzheimer’s is known to damage the brain, causing it to shrink as brain cells die and connections are lost. But the degree of brain damage does not always correlate with how intact thinking and memory skills remain. And many older people whose brains are filled with plaques and tangles, and in whom brain scans indicate likely Alzheimer’s disease, continue to function relatively well.
Other studies suggest that if two people have the same degree of brain damage from Alzheimer’s disease, memory and thinking skills are better preserved in the person with the larger head circumference. And some, but not all, studies suggest that people with larger brains, estimated by a larger head circumference, are less likely to have cognitive problems in old age.
Many factors besides head and brain size are involved in the development of Alzheimer’s disease. Genetics, age, level of education and previous head injuries can all affect Alzheimer’s risk. Regular exercise and a heart-healthy diet may also help to keep the memory sharp in old age.
R. Perneczky, MD, S. Wagenpfeil, PhD, K.L. Lunetta, PhD, et al: Head circumference, atrophy, and cognition: Implications for brain reserve in Alzheimer disease. Neurology, July 2010, Vol. 75, pages 137-142.