As people get older, the male brain shrinks faster than the female brain, a study has found.
But whether the greater shrinkage has any effect on how older men think or behave is not known, researchers said. Nor do scientists have an explanation for what makes anyone's brain get smaller, or why women seem to retain more of their brain tissue."Our work has generated a good laugh," said Dr. Edward Coffey, chairman of the psychiatry department at the Henry Ford Health System in Detroit and the chief author of the new study. "Women say, `So? What's new?' Men say, `Hogwash!' or, as one young man recently commented, `Bummer!' "
But the finding could provide important clues for understanding differences in how people age, Coffey said in a telephone interview.
"What makes one neighbor, who is 75, stay sharp as a tack whereas another neighbor, who is 60, forgets everything?" he asked. By looking at subtle differences in brain structure as men and women age, Coffey said, it may be possible to discover why some people age better than others.
The study appears in the February issue of The Archives of Neurology.
The findings buttress previous results from a half-dozen studies showing that there are greater age-related changes in the brains of men than in women, said Dr. Sandra Witelson, an authority on brain anatomy and a professor of psychiatry at McMaster University in Hamilton, Ontario.
Many of those studies have looked to levels of education, exercise or nutrition to explain differences, Dr. Witelson said, but the latest findings suggest that it might now be possible to see if structural changes lead to subtle differences in cognition.
The study looked at the brains of 330 healthy people 65 to 95 years of age through the use of magnetic resonance imaging, a technique that reveals brain anatomy in exquisite detail. In general, men's brains are bigger than women's because men are larger, Coffey said. But after allowing for such factors, it is possible to compare the size of various brain regions and to look for differences.
One measure is the cerebral spinal fluid, a clear, watery substance that bathes the brain's outermost layer, called the cortex, and circulates between various cavities in the brain's deeper regions. As the brain shrinks, Coffee said, the amount of fluid increases to fill the gap.
Everyone loses brain mass as he or she ages, Coffey said. Men just lose more of it. Around the cortex, older men show an average 32 percent increase in the cerebrospinal fluid. Older women show a 1 percent increase in fluid.
Fluid around a major fissure near the front of the brain, where memory and planning functions are carried out, increased by 80 percent in men and by only 37 percent in women.
The people in the study were not demented and their ability to concentrate was fine, Coffey said, but the men's brains look worse than women's.
How to explain this apparent paradox? "It may be that men are better able to tolerate brain shrinkage without showing the effects," he said.
Such age-related changes in brain size could be normal and have little or no effect on memory and thinking, or they could indicate that brain cells are dying and that a person's cognitive functions are declining, Coffey said.
Women might show a slower decline, he said, because they are protected by estrogen, a hormone known to protect brain cells and to lower the risk of Alzheimer's disease in women.