Thyroid Hormone levels Linked to Alzheimer's Disease in Older Women

Older women who have high or low levels of the thyroid hormone thyrotropin have more than twice the risk for the development of Alzheimer's disease vs those with more moderate thyroid hormone levels, according to a new study.

The study, published in the July 28 issue of the Archives of Internal Medicine, did not find an association between extreme thyroid hormone levels and Alzheimer's disease in men.

Although still hypothetical and subject to verification by further research, the results of this study suggest that it might be time to question whether target thyroid hormone levels (now typically between 0.5 and 5.0 mIU/L) should be narrowed to a more moderate range, said Zaldy S. Tan, MD, MPH, of Hebrew SeniorLife, Beth Israel Deaconess Medical Center and Harvard Medical School in Boston, Massachusetts.

Thyroid hormone function is intricately linked to the central nervous system. Adults with hypothyroidism are more prone to depression, whereas those with hyperthyroidism are subject to confusion. Also, recent studies have related thyroid dysfunction to an increased risk for irreversible dementia. "So we know there are some connections (between thyroid function and cognition), but I don't think anyone has figured out yet what the exact connection is," said Dr. Tan.

Would maintaining a narrower range of thyroid hormone levels prevent Alzheimer's disease? This question will take some time to answer. Although thyroid dysfunction is linked to dementia, depression, and other cognitive problems, "whether maintaining hormone levels within limits will actually prevent dementia I think might be a big jump," said Dr. Tan. "That will have to be proven in clinical trials."

Although it is known that long-term or chronic stress can affect the brain’s learning and memory region, a new finding discovers short-term stress, lasting as little as a few hours, can also impair brain-cell communication in these critical areas.

They found that rather than involving the widely known stress hormone cortisol, which circulates throughout the body, acute stress activated selective molecules called corticotropin releasing hormones, which disrupted the process by which the brain collects and stores memories.