CLINICAL THYROIDOLOGY FOR PATIENTS
A publication of the American Thyroid Association
Summaries for Patients from Clinical Thyroidology by Ernest Mazzaferri, MD MACP
Table of Contents
THYROID HORMONE THERAPY
L-T4 is levothyroxine, the standard drug for treatment of hypothyroidism and thyroid cancer
Gastrointestinal malabsorption of thyroid hormone Many things interfere with levothyroxine (L-T4) absorption, such as iron, bile acid–binding resins, cholestyramine and colestipol, over-the-counter drugs containing iron and calcium, gastric conditions such as achlorhydria, and food ingestion around the time L-T4 is taken. Many other drugs and conditions impair absorption of L-T4.
What is the study about? Coffee interferes with the intestinal absorption of levothyroxine.
The full article title: “Altered Intestinal Absorption of L-Thyroxine Caused by Coffee.” It is in the March 2008 Issue of Thyroid (volume 18 Issue 3, pages 293-301). The authors are S Benvenga, L Bartolone, MA Pappalardo, A Russo,D Lapa, G Giorgianni, G Saraceno, G., and F Trimarchi.. The abstract can be obtained from: http://www.ncbi.nlm.nih.gov/pubmed/
What is known about the problem being studied? Many things interfere with gastrointestinal absorption of L-T4 (See Box) The authors of this study have previously reported cases of delayed intestinal absorption of L-T4 and have thus been more than usually attentive to this problem, eliciting detailed histories from their patients about the use of other drugs and the dietary habits patients follow when taking L-T4.
What was the aim of the study? The authors found that several patients were consistently drinking coffee or espresso to facilitate swallowing L-T4 pills or were taking L-T4 with water followed shortly by drinking coffee or espresso, suggesting that this might be the cause of the problem. The study was designed to test gastrointestinal absorption of L-T4 in patients taking L-T4 while simultaneously drinking coffee or espresso
Who was studied? The study subjects were eight patients, all of whom were women. Their mean age was 45 years and their serum TSH levels were 2.7μIU/ml (normal range, 2.9 to 55). Ten healthy volunteers, four men and six women aged 24 to 52 years, were also studied as controls.
How was the study done? L-T4 absorption was tested in patients divided into several groups, some taking L-T4 with water alone, others using espresso alone to help sallow their L-T4 pills, and in other cases volunteers used water alone with L-T4 and espresso 1 hour later, and lastly L-T4 was taken with bran in water.
What were the results of the study? The effect of espresso on L-T4 absorption was variable, and was present only if espresso was swallowed simultaneously with the L-T4, but not 60 minutes later. Taking L-T4 with espresso lowered the average and peak incremental rise of serum T4 by a minimum of 25% in one patient, to a maximum of 57% in patient in another patient. Reduction in the maximal incremental rise in serum levels ranged from 14% in one patient to 49% in another, while overall reduction ranged from 23% to 55%. Compared to water, espresso delayed the peak serum increase in serum T4 from 0 in one patient to 90 minutes in another. The study clearly showed that drinking espresso or coffee may interfere with intestinal absorption of L-T4 if one drinks it with or shortly after levothyroxine is taken. This pattern of taking espresso or coffee with L-T4 was highly consistent among the eight study patients. The effect was significant, but is not as severe as that produced by Maalox or by bran ingested at the time L-T4 is taken.
How does this compare with other studies? Approximately 62% to 82% of the oral dose of levothyroxine is absorbed by the upper intestine. The rate of absorption can be estimated by simply giving large oral doses of thyroid hormone. This has led to the discovery of a number of conditions that can lead to malabsorption of thyroid hormone.
What are the Limitations of this study? Coffee does not change the gastric pH, nor does it impair gastric emptying and intestinal transit in normal volunteers. Because the study is retrospective, it relied on the recollections of patients rather than a systematic recording of the timing of meals and coffee ingestion.
What are the implications of this study? The observations are robust enough, and the recommendations simple enough to warn patients about this problem and to add coffee to the list of things to be avoided at the same time that L-T4 is taken.