Is Subclinical Hypothyroidism Linked to Cognitive Impairment in the Elderly?

Cognitive impairment illustrated by broken mind vectorIt’s well known that although overt hypothyroidism is linked to reversible dementia in the elderly population, the connection between subclinical hypothyroidism and cognition is a controversial issue.

Researchers investigated the link between subclinical hypothyroidism and cognitive impairment in the elderly. In particular, they looked at selective attention and long-term memory.

Results of their study were published online in early March 2012 in the article “Subclinical hypothyroidism and cognitive dysfunction in the elderly.” The article will appear in an issue of the journal Endocrine, Metabolic & Immune Disorders - Drug Targets.

The research team identified 337 patients (there were 177 men and 160 women) to participate in the study; they didn’t include patients who had thyroid dysfunction or those who were treated with medications that had an impact on thyroid function. The mean age of the participants was 74.3 years old.

Researchers used multiple tests—the Mini Mental State Examination (MMSE), the Prose Memory Test (PMT), and the Matrix Test (MT)—to help them determine the association between subclinical hypothyroidism and cognitive function.

Using the MMSE, they noted that the scores were significantly lower in the group of patients who had subclinical hypothyroidism than in those patients who were euthyroid (p<0.03). Additionally, researchers observed that the patients who had subclinical hypothyroidism had a probability of about 2 times greater of developing cognitive impairment (relative risk [RR]=2.028; p<0.05).

Researchers found that the PMT scores were significantly lower in patients who had subclinical hypothyroidism (p<0.04).

They noted that for the MT scores, performance was slightly reduced in the patients who had subclinical hypothyroidism (not significant [NS]).

Researchers determined that thyroid-stimulating hormone (TSH) was negatively linked to MMSE (p<0.04), PMT (p<0.05), and MT (NS) scores, but they didn’t find a link between free thyroxine (FT4) and free triiodothyronine (FT3) and MMSE, PMT, and MT scores. They concluded that in the elderly population, subclinical hypothyroidism is linked to cognitive impairment. However, the impact of subclinical hypothyroidism on specific aspects of cognition—especially long-term memory and selective attention—is not as apparent.

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