Endocrine Abstracts

JOINT700

Background: Levothyroxine (LT4) co-ingestion with food may lead to reduced absorption and increased thyroid-stimulating hormone (TSH) levels. Therefore, fasting ingestion is recommended. Yet, in a recent study we found that the majority of patients are burdened by fasting ingestion. Therefore, we aimed to investigate whether dose-adjusted, non-fasting LT4 ingestion could achieve stability of TSH levels comparable to fasting ingestion.

Methods: Patients were randomized to a fasting group, taking LT4 as usually recommended, or a non-fasting group, ingesting LT4 with breakfast after increasing the baseline LT4 dose by 15% to compensate for reduced absorption due to non-fasting ingestion. TSH, free T4 (FT4) and total T3 (TT3) levels were measured every six weeks until study completion. Patients were followed for 12 weeks in case two consecutive TSH levels fell within reference range. If TSH was out of range, follow-up was extended to 18 or 24 weeks. TSH stability was defined as a mean difference in TSH from baseline to study end ranging between -1 and +1mIU/l.

Results: Eighty-eight patients (80.7% female, median age 62y [IQR:49-69]) were randomized: 43 to the fasting and 45 to the non-fasting group. No significant differences were observed between the fasting and non-fasting group in mean difference of TSH (+0.22±1.00mIU/l vs. +0.22±0.92, p=NS), FT4 (-0.48±2.41 vs. -0.96±2.75pmol/l, p=NS) and TT3 (0.07±0.18 vs. 0.08±0.22nmol/l, p=NS), respectively. TSH stability was achieved in 71.8% of the fasting group and 73.2% of the non-fasting group (p=NS). By study end, 93.3% of the non-fasting group preferred to continue taking LT4 with breakfast.

Conclusion: Dose-adjusted, non-fasting LT4 ingestion achieved TSH stability comparable to conventional fasting LT4 ingestion. Therefore, this could be considered as an alternative to fasting LT4 ingestion.