Hormone therapy appears to affect the brain differently depending on the age of the woman when she receives it, researchers reported Thursday.
Hormone-replacement therapy for women has been the subject of considerable debate. Studies have shown both pros and cons. But hormone use has declined in the last decade because a major study on the issue, the Women's Health Initiative, found that the risks of taking hormones appeared to outweigh significantly the benefits in older postmenopausal women. Among the findings was that beginning hormone therapy in women ages 65 and older led to a twofold higher risk of dementia.
Questions remain about the effect of hormones if taken at a younger age - among perimenopausal (the phase before menopause when hormones decline and fluctuate) or menopausal women in their early 50s. The new study, published in the Annals of Neurology, supports the idea that hormones can affect dementia risk differently depending on the age of the woman when she takes them.
Kaiser Permanente researchers examined data from members in Northern California from 1964 to 1973, among women 40 to 55 years old. The study examined whether hormones were used at midlife - defined in this study by the average age of 48.7 - or in late life, defined as age 76. Compared with women who never used hormones, those taking hormones only at midlife had a 26 percent decreased risk of dementia. This link held true even when the researchers controlled for other factors that contribute to dementia, such as high cholesterol and stroke.
However, taking hormones in late life may counteract whatever benefits are seen by taking hormones at midlife, the authors said. Women taking hormone therapy only in late life had a 48 percent increase in dementia. Women using hormones at both midlife and late life did not differ in their dementia risk from women who didn't take hormones.
"The reduced risk of dementia associated with midlife hormone therapy use only lends support to the notion that it is not only early postmenopausal use of hormone therapy that is protective, but that use should also be limited to a few years," the authors wrote.
Animal studies suggest that estrogen benefits brain health, and observational studies have shown that women who take hormones are less likely to develop dementia later in life. But studies such as the Women's Health Initiative dashed hopes that hormones protected against cognitive impairment. Research now is focusing on whether there is a "critical window" for use - a specific time of life when hormones would do more good than harm.
Explore further: Gonorrhoea and syphilis in Norway in 2014