TAMPA, Fla., Oct. 22 (UPI) -- University of South Florida researchers say the size of a person's head may be one risk factor for Alzheimer's disease.
People with a gene predisposing them to Alzheimer's who also have small heads were 14 times as likely to develop the disease than people
without that gene variant and with larger heads, said Amy Borenstein Graves, professor of epidemiology and biostatistics at the university in Tampa.
The researchers believe people with smaller brains may be less able to compensate for the brain cell damage that is a hallmark of
Alzheimer's disease, so symptoms like memory loss occur earlier in these people. The idea is, however, still controversial.
To test the theory, Borenstein Graves and her colleagues followed 1,869 healthy Japanese Americans age 65 or older for an average of about four years. During that time, 59 people developed Alzheimer's disease.
The researchers measured the circumference of people's heads around the eyebrows and across the widest part of the skull. The third of study
participants with the smallest head measurements were slightly more likely to develop Alzheimer's than were the third of people with the largest heads, but the results might have been due to chance, Graves reported. People with a gene variant called alipoprotein E 4 or ApoE4, a known risk factor for the disease, were 4.8 times more likely to be diagnosed with Alzheimer's.
Alzheimer's developed most often among people with the ApoE4 gene variant and a small head circumference, the team reported in the Oct.
23 issue of Neurology.
"Head circumference probably doesn't influence the pathology (the underlying biological damage) of Alzheimer's, but is a mitigating factor
in the development of symptoms," Graves said. While brain growth is controlled in part by genetics, it also may be influenced by
nutrition, infection, family size, and birth order, she said.
This study is not enough to definitively link smaller head size with an increased risk of Alzheimer's, said Neill Graff-Radford, chair
of the department of neurology at the Mayo Clinic in Jacksonville, Fla. For one thing, a relatively small number of people developed Alzheimer's.
Also, the study also shows "smaller head
size is linked with older age, female gender, and less education," Radford said.
Previous studies have suggested people who have more education tend to be resistant to Alzheimer's disease, while women are more susceptible than are men. Increasing age probably is the biggest
risk factor for Alzheimer's, while poor nutrition among children might explain their smaller heads, Radford said.
"While it is plausible that head size might be related to Alzheimer's disease," he said, "it's still far from proven."
"The question of brain reserve remains an open question," said Bill Thies, vice president for medical and scientific research at the
Chicago-based Alzheimer's Association. "While head circumference may, long term, give us a better idea who should get preventive medicine, we
don't have any such medicine available right now."
(Reported by Damaris Christensen in Washington.)