Levothyroxine is commonly used to treat hypothyroidism. This study investigates how far the intake of L-T4 influences body composition, energy expenditure, respiratory quotient as well as strength, endurance and mobility in premenopausal women who suffer from subclinical hypothyroidism. Twenty-five women (27.36±5.77 years) with subclinical hypothyroidism were included in the study. The intake of levothyroxine was assumed. Subjects were examined immediately after study inclusion, after two months of levothyroxine use, and after TSH was fully adjusted to the reference range. In all measurements TSH, fT3 and fT4 were determined, body weight, body composition, energy expenditure and the respiratory quotient were measured, and a test battery was performed to identify strength, mobility and endurance capacity. TSH decreased from 5.95±0.99 μIU/ml at study inclusion to 1.2±0.33 μIU/ml after final trial. No change in weight, BMI, muscle mass, fat mass, energy expenditure and respiratory quotient was observed (p>0.05). A significant improvement in chest press (p=0.002), leg extension (p<0.001), right-hand grip strength (p=0.009) shoulder mobility (p<0.001), hip mobility (p=0.07), explosive strength (p=0.041) and the anaerobic threshold (p=0.13) was identified. Likewise, a non-significant (p=0.298) increase in left-hand grip strength could be detected.In summary, although levothyroxine does not positively affect body composition, energy expenditure and respiratory quotient, it can improve strength, mobility and endurance performance. For this reason, treatment with levothyroxine is recommended to improve exercise capacity in subclinical hypothyroidism.

Received: 09 July 2022

Accepted after revision: 11 October 2022

Article published online:
29 November 2022

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