Subclinical Hyperthyroidism Linked to Frailty in Older Men

Miriam E Tucker

November 16, 2015

Subclinical hyperthyroidism, but not subclinical hypothyroidism, may be associated with increased odds of frailty among older men, a recent study suggests.

The findings were published online October 23, 2015 in the Journal of Clinical Endocrinology and Metabolism by Vanessa S Virgini, MD, of the department of internal medicine, University Hospital of Zürich, Switzerland, and colleagues.

In the study of 1455 community-dwelling men older than 65 years, those with subclinical hyperthyroidism at baseline were more likely to be frail, while those with subclinical hypothyroidism were not.

"Our paper raises the possibility that subclinical hyperthyroidism may be more likely among frail elderly men but does not address the issue [of whether] treatment improves their frailty," principal investigator Douglas C Bauer, MD, professor of medicine and epidemiology and biostatistics at the University of California, San Francisco, told Medscape Medical News.

While the Osteoporotic Fractures in Men (MrOS) study was conducted only in men, it's likely that similar results would be seen in women, Dr Bauer said.

First Work to Examine Subclinical Thyroid Function and Frailty

The researchers say this is the first research, to their knowledge, to investigate the link between subclinical thyroid dysfunction and frailty in older men.

The prospective MrOS study involved those older than 65 years. Among the 1455 men, 1.8% had subclinical hyperthyroidism and 7.0% had subclinical hypothyroidism, while the rest were euthyroid. (There were too few men with overt disease to analyze in this population-based study, Dr Bauer explained.)

In all, 20.3% of the men reported at least one fall in the previous year.

The researchers assessed the cross-sectional relationship between baseline thyroid function and three categories of frailty status (robust/intermediate/frail), as well as the prospective association between baseline thyroid function and subsequent frailty status and mortality after a 5-year follow-up.

At baseline, 44.4% of the men were considered robust, 46.4% were intermediate, and 9.2% were defined as "frail," based on measures of grip strength, sarcopenia, and responses to questions on two questionnaires assessing medical outcomes and physical functioning in the elderly.

At baseline, men with subclinical hyperthyroidism had a greater risk for frailty than euthyroid subjects (adjusted odds ratio [OR], 2.48), and the association was particularly strong among the men younger than 74 years of age (OR, 3.63).

There was no significant association between baseline thyroid status and frailty over the 5-year follow-up period, however. A pattern of increased risk for developing sarcopenia was seen among those younger than 74, but it wasn't statistically significant, Dr Virgini and colleagues note.

There was no link between subclinical hypothyroidism and frailty, which was a surprise, because the researchers say they had expected to find an association.

The authors propose that the baseline association between subclinical hyperthyroidism and frailty, particularly among men aged 74 years and under, might have to do with increased risks for osteoporosis, cognitive decline, cardiovascular events (including stroke), prothrombotic diathesis, elevated free T4 levels, and/or weight loss, all of which have been linked to hyperthyroidism.

The reason for the lack of significant association seen among those older than 74 isn't clear but might relate to their having a greater likelihood of undergoing more intensive medical follow-up and of receiving diagnosis and treatment for cardiovascular conditions, while the younger men may have remained undiagnosed for a longer time, the authors speculate.

However, they also note that the results remained unchanged after adjustment for osteoporosis, history of stroke, myocardial infarction, and Mini Mental Score.

So it's also possible the findings were due to chance; in addition, the number of men with subclinical hyperthyroidism under 74 was small, comprising only 13 men, they note.

"Future studies with higher prevalence of subclinical hyperthyroidism and subclinical hypothyroidism are needed," they conclude.

The Osteoporotic Fractures in Men study is supported by the National Institutes of Health. Dr Bauer has no relevant financial relationships. Disclosures for the coauthors are listed in the paper.

J Clin Endocrinol Metab. Published online October 23, 2015. Abstract

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