Hormone treatments commonly used by menopausal women appear to accelerate brain shrinkage, according to two new studies.
The research, appearing in the January 13 issue of the medical journal Neurology, showed greater than typical brain tissue loss in women 65 and older.
Previous studies showed that older women on progestin-based drugs had decreased thinking skills and memory, and were more likely to suffer from dementia and brain diminished function.
Doctors long had believed that the impairment had been caused by tiny vascular brain lesions caused by hormonal treatments.
But the new research using MRI scans of women's brains appears to show a reduction in brain tissue in regions critical to memory for women who used the hormones.
"Our findings suggest one possible explanation for the increased risk for dementia in older women who had previously taken post-menopausal hormone therapy," said Laura Coker of Wake Forest University Baptist Medical Center, a lead researcher on one of the studies.
A second study found that women who had taken hormone therapy had slightly smaller brain volumes in the brain's frontal lobe and the hippocampus -- both critical areas for thinking and memory skills.
"Our findings suggest that hormone therapy in older post-menopausal women has a negative effect on brain structures important in maintaining normal memory functioning," the study concluded.
"However, this negative effect was most pronounced in women who already may have had some memory problems before using hormone therapy," the research found.
The study tracked more than 1,400 women, ages 71 to 89, who had previously participated in a hormone therapy study for between an average of four to six years.
The findings suggest that hormone therapy to treat the symptoms of menopause should be used only when deemed absolutely necessary, and then at the lowest dose and for the shortest possible time.