Thyroid stimulating hormone (TSH) and free thyroxine (FT4) levels have no relationship with bone turnover markers or hip fractures in healthy older men, endocrinologists in WA have shown.

The University of WA study comprising more than 3,000 mostly euthyroid men, and a small proportion with subclinical hyperthyroid disease, found TSH and FT4 had no association with total and undercarboxylated osteocalcin, N-terminal propeptide of type I collagen or collagen type I C-terminal cross-linked telopeptide.

As well, TSH and FT4 had no association with the 161 incident hip fractures identified during about 10 years of follow-up – either in euthyroid men or those with subclinical thyroid disease.

The findings are inconsistent with other studies, which the researchers suggested might be because they adjusted for frailty in a population with a median age of 77 years.

“Thyroid dysfunction may be associated with symptoms of frailty, such as fatigue, reduced muscle strength and weight change, and higher FT4 has previously been shown to be associated with frailty in older euthyroid men.”

“This relationship between thyroid function and frailty may therefore confound the previously reported associations between thyroid function and fracture risk.”

In the context of a known link between overt hyperthroidism and elevated bone turnover makers, the researchers said their results suggested a threshold for the effect of thyroid functioning on bone.

And their findings in men notably contrasted with other findings in females.

“These studies support the hypothesis that postmenopausal women may be more susceptible to the skeletal consequences of excess thyroid hormones than elderly men,” they said.