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Science and Research

The Link Between Hormones and Alzheimer's Disease

Research Explores Estrogen’s Role in Brain Health

Alzheimer’s disease is the sixth-leading cause of death in the United States. According to the Alzheimer’s Association, nearly two-thirds of Americans with Alzheimer’s are women.

Although this could be attributed to the fact women tend to live longer than men, there may be more to this gender difference: specifically, the connection to women’s hormones, including estrogen.

A recent study shows there could be a link between oral hormone therapy and Alzheimer’s disease in postmenopausal women. Borna Bonakdarpour, MD, behavioral neurologist at Mesulam Center for Cognitive Neurology and Alzheimer Disease and Northwestern Memorial Hospital, is an expert in the field of Alzheimer’s. Here, Dr. Bonakdarpour weighs in on this study’s implications.

A Look at Recent Research

Conducted in Finland, the study looked at about 85,000 postmenopausal women who were diagnosed with Alzheimer’s disease between 1999 and 2013. Scientists determined that there was a 9 to 17 percent increased risk for Alzheimer’s disease in women who received oral hormone therapy. In women who were younger than 60 when they started oral hormone therapy, the risk increased if the therapy was administered for more than 10 years.

Hormone therapy is used to manage hot flashes, night sweats and disruptive sleep, conditions caused by changing estrogen levels during menopause.

The study itself did not determine a conclusive link between oral hormone therapy and Alzheimer’s disease. While dementia may have other causes, it’s possible that hormone therapy speeds up the progression of symptoms.

“This is an impressive finding. It is possible that long-term administration of a hormone that women are not naturally exposed to after menopause may be harmful,” says Dr. Bonakdarpour. “The level of estrogen hormone in the blood fluctuates throughout women’s menstrual cycle. By providing this medication, we provide a steady stream of the hormone that does not follow the usual fluctuations. This unusual availability of estrogen might explain why women with hormone therapy had worsened cognition, but this is all speculation.”

Dr. Bonakdarpour cautions that the diagnosis of Alzheimer’s disease in this study was clinical and not using biomarkers currently available. “In the last 20 years, research and technology has changed the way we can diagnose Alzheimer’s. We now make the diagnosis of Alzheimer’s disease using spinal fluid analysis and by amyloid positron emission tomography (PET). In the absence of these techniques, we can be sure of pathologic diagnosis of Alzheimer’s disease only in about 85 percent of participants of this study. Lack of this information in this study makes generalizations about relationship between hormones and Alzheimer’s disease somehow difficult.”

Hormones and Their Potential Link

These findings support an ongoing look at the role of hormones in memory loss, including Alzheimer’s disease.

Estrogen is a hormone that helps protect the brain, keeping it healthy and stimulating growth. When estrogen levels drop, it could mean a loss of protection to the brain, though the exact reason is unknown. On the other hand, based on evidence presented by animal studies, it’s suggested that those with low estrogen are less likely to develop amyloid protein; one of the hallmark characteristics of Alzheimer’s disease is a buildup of amyloid plaques between nerve cells. “In this case, estrogen in the brain may help clear abnormal proteins involved with the development of

Alzheimer’s disease,” says Dr. Bonakdarpour. It seems that the major factor is when hormones are administered and for how long.

A deficit in estrogen has been connected to a higher incidence and earlier decline from cognitive impairment or dementia. For example, individuals undergoing chemotherapy for breast cancer get hormone-suppressing medication that reduces the effect of estrogen, and these patients often experience cognitive problems.

“There’s no doubt that younger people who are low in estrogen need to get the hormones. It’s important because it promotes a healthier brain as they age,” says Dr. Bonakdarpour. However, timing is important. “Taking estrogen may have detrimental effects when taken after menopause.”

The Bottom Line

When it comes to hormone therapy, the benefit may outweigh the risk, but it should be used cautiously. “Hormones should be used if they it promote quality of life, and women can take them for short-term relief,” says Dr. Bonakdarpour. But he encourages individuals to remain under the supervision of their physician and periodically evaluate when to stop the medication.

Borna Bonakdarpour, MD
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