Morning exercise affects the absorption of oral levothyroxine: a single center pilot study

Levothyroxine (LT4) is the first-line hormone replacement therapy for hypothyroidism. Several factors which have an influence on oral LT4 absorption have been previously described; however, the influence of exercise on oral LT4 absorption has not been reported, yet. It was aimed to investigate the possible effect of morning exercise, right after LT4 ingestion, on the absorption of LT4 tablets in this study.

Patients with primary hypothyroidism who fulfilled the inclusion criteria were offered to participate in a 6-week morning exercise programme and those who agreed to participate were enrolled in our study. Patients were required to have a walk for 30 min with a regular speed right after taking their daily LT4 treatments and start having breakfast the first hour after LT4 intake. Pre- and post-exercise TSH levels were recorded and TSH percentage change was calculated.

All patients had decreased TSH levels after the exercise programme. There was a significant decrease in TSH levels (p < 0.001). A significant positive correlation between TSH percentage change and daily dose of LT4 per kg of body weight was also shown.

This is the first study which demonstrates the significant positive effect of morning exercise on the absorption of LT4 tablets. In addition to that, it was also found that as the daily dose of LT4 increases, the percentage decrease of TSH level becomes greater.