New research suggests that some forms of hormone replacement therapy (HRT) can cause brain shrinkage in postmenopausal women.

Susan Resnick, PhD, of the National Institute on Aging in Baltimore, and colleagues took MRI brain scans of 1,400 women aged 71 to 89 one to four years after the end of the Women's Health Initiative Memory Study (WHIMS). Results showed that brain volume was 2.37 cubic centimeters lower in the frontal lobe and 0.10 cubic centimeters lower in the hippocampus – both key areas of the brain involved in thinking and memory – in women who had taken estrogen with or without progestin than in those who had taken a placebo. Loss of volume in the hippocampus is a known risk factor for dementia.

However, the results also showed that the effects of HRT on brain volume were more apparent in women who may have already been experiencing memory problems before they used HRT. “This suggests that estrogen may adversely affect thinking skills among women whose brains may already be beginning a neurodegenerative disease process,” said Dr Resnick.

Resnick SM, Espeland MA, Jaramillo SA, et al. Postmenopausal hormone therapy and regional brain volumes. The WHIMS-MRI Study. Neurology 2009;72:135-142.

News release: Hormone Therapy Linked to Brain Shrinkage, But Not Lesions. American Academy of Neurology. January 12th 2009.