New research suggests that postmenopausal women with elevated estrogen levels have more than double the risk of developing dementia, especially if they also have diabetes. Estrogen levels were about 70 percent higher in women with diabetes who also had dementia compared to those without dementia.

Published in Neurology, the researchers used a data from a large study that included more than 5,600 postmenopausal women aged 65 or older. The participants’ measured the estrogen levels in the individuals without dementia and not on hormone replacement therapy or medication that boosts estrogen levels. Four years later, the participants were followed up and 543 women who had no dementia were compared with 132 who did. The researchers also looked at risk factors, including high-blood pressure, blood clotting and other indicators of heart health.

The results were a surprise, said lead investigator Dr. Pierre-Yves Scarabin, director of research at the French National Institute of Health and Medical Research (INSERM) in Villejuif, France. "We found an association between high levels of endogenous estrogen and the risk of dementia in older women not using hormone therapy," he said.

Estrogen was long viewed as beneficial for women’s health, with an ability to reduce post-menopausal symptoms and have progressive effects on the heart and brain. "While it was long believed that estrogens -- either endogenous or therapeutic -- were good for women's health, especially for the heart and brain, our study together with other current data challenge this dogma," said Scarabin.

According to the International Diabetes Federation, approximately 382 million people worldwide have diabetes, and that number may rise to an estimated 592 million by 2035. Also, Alzheimer’s Disease International estimates that 44 million people worldwide suffer from dementia, a number expected to grow to 76 million in 2030.

"Importantly, our study reported, for the first time, a dramatic rise in future dementia risk in women with both diabetes, which is a well-known risk factor for dementia, and high estradiol levels," Dr. Scarabin added.