MON-606 Different Relationships between Thyroid Stimulating Hormone and Muscle Strength According to Sex and Age in Euthyroid Koreans (KNHANES 2014-2015)

Background: Changes in muscle mass and strength can be caused by multiple endocrine factors including thyroid dysfunction. However, the association of thyroid function with muscle strength in euthyroid individuals was rarely reported. Therefore, we investigated the relationship between thyroid function and hand grip strength (HGS) in euthyroid Koreans, especially according to sex and age. Methods: This was a population-based, cross-sectional study from the Korea National Health and Nutrition Examination Surveys including 3,493 Koreans (1,810 men and 1,683 women) aged 19 years or older. Serum thyroid stimulating hormone (TSH) and free thyroxine (FT4) were measured. HGS was measured using a digital grip strength dynamometer. Results: TSH, but not FT4, was significantly associated with HGS in men. Neither TSH nor FT4 was associated with HGS in women. TSH showed a negative association with HGS in men under 65 years old (n = 1,699; β = -0.566, P = 0.008), while a positive association was observed in men aged 65 years or older (n = 111; β = 1.158, P = 0.010) after adjusting for confounders. As the TSH tertile increased, HGS decreased in men under 65 years old (P for trend = 0.010), while it increased in men aged 65 years or older (P for trend = 0.009) after adjusting for confounders. Odds ratios for the lowest quartile of HGS increased and decreased in the highest tertile of TSH of men under 65 years old (OR 1.66, 95% CI 1.10-2.50, P = 0.006) and of men aged 65 years or older (OR 0.18, 95% CI 0.03-0.97, P = 0.034), respectively, after adjusting for confounders. Conclusions: In euthyroid Koreans, TSH was significantly associated with HGS only in men and the relationships were different according to age. These findings suggest an sex- and age specific direct impact of thyroid stimulating hormone on muscle strength in euthyroid individuals.