Summary

Previous work has linked thyroid functioning to cognitive impairment. In a new study, researchers at Beth Israel Deaconess Medical Center have measured levels of the hormone thyrotropin in a group of women and looked at incidence of dementia during follow up. This showed that lower and higher levels of the hormone were linked with greater risk.

Introduction

Alterations in hormone levels often have an effect on cognitive functioning and could be linked to the risk of dementia. For example, having an over or under-active thyroid gland has long been known as a reversible cause of cognitive impairment. Therefore, screening of thyrotropin levels is an important part of an assessment in suspected dementia. Thyrotropin is a hormone secreted by the pituitary gland which controls the function of the thyroid gland. Also, high and low levels of thyrotropin have been linked to poorer cognitive performance in some studies (though other studies have not confirmed this). This background evidence suggests that it is important to explore further the link between thyrotropin and Alzheimer's disease, in case correcting thyroid function could possibly reduce the risk of dementia.

What was done

Researchers at the Beth Israel Deaconess Medical Center and Harvard Medical School carried out an investigation as part of the long running Framingham Study which was set up to looked at cardiovascular risk factors. They measured thyrotropin levels in a group of 1864 individuals of average age 71 years of whom 59 percent were women. During follow up of 12.7 years, on average, cases of Alzheimer's disease were recorded.

What was found

During the follow up time, 209 participants, of whom 142 were women, developed Alzheimer's disease. Women in the lowest and highest thirds of thyrotropin concentrations had about twice the risk of developing the disease compared to those in the middle third. There was no such association among male participants.

What this study means

The researchers point out that it is not clear whether the altered thyrotropin levels actually cause the increase in risk of Alzheimer's disease, or whether they are a result of it. Changes in the brain during dementia could affect the pituitary gland, which secretes the hormone. However, it might be that abnormalities in the levels of the hormone are harmful to the brain. Further work should shed further light upon what is likely to be a complex connection between the thyroid and the brain.