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The effect of thyroxine is greater when taken at bedtime than in the morning in patients with hypothyroidism
The background of the study. Patients with hypothyroidism who are taking thyroxine (T4) are often advised to take their daily dose before eating in the morning. This study was done to determine whether ingestion of T4 at different times resulted in different patterns of 24-hour serum thyroid hormone and thyrotropin (TSH) concentrations.
How the study was done. The study subjects were 11 women with hypothyroidism who were taking T4 (mean dose, 121 µg daily) either 30 minutes before breakfast or at bedtime. Most women were studied while taking their usual dose of T4 30 minutes before breakfast and again after they had taken it at bedtime (2200 hours) for two months; the sequence was reversed in the others. For each study, blood samples for measurements of serum TSH, total T4, free T4, and total triiodothyronine (T3) were obtained hourly for 24 hours. The women ate at 0730, 1230, and 1730 hours, were ambulatory during the day, and went to bed at 2200 hours.
The results of the study. The average hourly serum TSH values were lower and the hourly serum free T4 and total T3 concentrations were slightly higher when T4 was taken at bedtime than when it was taken in the morning (Table), but there were no differences in hourly serum total T4 concentrations.
| Table. Mean 24-Hour Serum TSH and Thyroid Hormone Concentrations in Patients with Hypothyroidism Taking T4 30 Minutes before Breakfast in the Morning and at Bedtime. | ||
| Serum | Morning | Bedtime |
| TSH (mU/L) | 5.1 | 1.2 |
| Free T4 (ng/dl) | 1.3 | 1.5 |
| Total T4 (µg/dl) | 8.9 | 9.4 |
| Total T3 (ng/dl) | 96 | 106 |
The 24-hour pattern of serum TSH concentrations, with higher values late in the evening and during the night and lower values during the day, was similar in both studies, despite the higher hourly values when T4 was taken in the morning.
The conclusions of the study. Serum free T4 and total T3 concentrations are higher and serum TSH concentrations are lower when T4 is taken at bedtime than early in the morning, suggesting that it is absorbed better when it is taken at night.
The original article. Bolk N, Visser TJ, Kalsbeek A, van Domburg RT, Berghout A. Effects of evening vs morning thyroxine ingestion on serum thyroid hormone profiles in hypothyroid patients. Clin Endocrinol (Oxf) 2007;66:43-8.
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| Thyroid Digest Index | | | March 2007 Thyroid Digest |
