Background: Untreated overt hypo- and hyperthyroidism can lead to detrimental effects on muscle tissue and physical performance, but it is still unclear whether subclinical hypo- or hyperthyroidism has clinically relevant effects on muscle function and physical performance. The objective of this study was to determine associations of thyrotropin (TSH) with grip strength and physical performance. Methods: A sample of 6196 participants from the Study of Health in Pomerania and the Berlin Aging Study II was included in this cross-sectional analysis. Handgrip strength was measured with a hand-held dynamometer and physical performance was assessed with the timed up and go (TUG) test. Results: Serum TSH levels were significantly inversely associated with handgrip strength (β -0.11; [95% confidence interval, CI, -0.18 to -0.03]; p < 0.05) in multivariable linear regression. Individuals with high (β -1.06; [95% CI -1.86 to -0.26]; p < 0.05) or low (β -0.99; [95% CI -1.70 to -0.28]; p < 0.05) serum TSH levels had a significantly lower handgrip strength than individuals with serum TSH levels within the reference range. There was no association between TSH and the TUG time. Age showed a significant influence on the association of TSH with grip strength and TUG time. Conclusions: Even mild disturbances of thyroid function might lead to a relevant decline in grip strength, particularly in young and middle-aged subjects. Mild subclinical hypothyroidism might not be that unfavorable with regard to physical function in terms of handgrip strength at older age. Further studies are needed to clarify causal relationships.
Keywords: age; functional status; grip strength; lifespan; thyroid function.