From InFocus Newsletter, December 2007 

 Every thyroid patient has heard the advice that, for best results, we should take our medication first thing in the morning, on an empty stomach, and wait at least 30 minutes to an hour before eating.  (And, also, that we should wait at least three to four hours before taking calcium or iron, which can interfere with thyroid hormone absorption).  But research reported in the journal Clinical Endocrinology found that taking the same dose of levothyroxine (i.e., Synthroid) at bedtime, as compared to first thing in the morning, might be better.

The small pilot study was prompted by observation that some patients had improved thyroid hormone profiles after they switched from taking their levothyroxine in the morning to bedtime.  The researchers also evaluated the impact of the change on the circadian rhythm of TSH and thyroid hormones and thyroid hormone metabolism.  The study, while small (12 subjects), was fairly conclusive in its findings, which the researchers said were "striking" and which have "important consequences for the millions of patients who take l-thyroxine daily."

The researchers reported that taking medication at bedtime, rather than in the morning, results in "higher thyroid hormone concentrations and lower TSH concentrations."  TSH decreased and Free T4 levels rose in all patients by changing thyroxine ingestion from early morning to bedtime, and T3 levels rose in all but one subject.  TSH decreased irrespective of the starting TSH levels, suggesting better absorption of the thyroid medication when taken in the evening.  Interestingly, the researchers found that the circadian TSH rhythm--the typical daily fluctuations of TSH that occur during a 24-hour period--does not vary.

The researchers have suggested that, given the results of the pilot study, a large double-blinded randomized study will need to be performed to confirm their results.

--Source: Excerpted from Mary Shomon, Your Guide to Thyroid Disease, About.com