Background
In overt thyroid disease, neuromuscular deficit has been reported. As skeletal muscle is one of main targets of thyroid hormone signaling, an association of thyroid function and muscle strenght could be expected. The aim of study is to evaluate the association of free thyroxine (FT4) and thyrotropin (TSH) with muscle strength, measured by hand grip strength, in national representative data.
Methods
The study utilized the sixth edition of the Korea National Health and Nutrition Examination Survey (KNHANES 2014-2015), which represent general health and nutritional status of Koreans. After exclusion of subjects with age less than 19 years, free T4 level out of normal range, a history of thyroid disease or cerebral disease, restricted activity and incomplete data, a total of 3503 were recruited.
Results
FT4 positively correlated with muscle strength (β coefficient=-12.84, p<0.001), while TSH did negatively (β coefficient=-0.37 p=0.002). After adjusting for several confounding factor such as age and BMI, statistical significance disappeared. However, subjects with BMI above 23, who were considered as overweight or obese in Asian, a negative correlation of TSH with muscle strength was found in a young age group (19-39 year-old) after adjustment for confounders (β coefficient=-0.56, p=0.021). In an old age group (40 or above 40 year-old), FT4 positively correlated with muscle strength (β coefficient=3.24, p=0.019).
Conclusion
In overweight and obese population, a significant association of thyroid function with muscle strength was observed in nation-wide representative data. High TSH in a young age group and low FT4 in an old age group could be risk factors for decreased muscle strength.