Altered intestinal absorption of L-thyroxine caused by coffee.
OBJECTIVE
To report eight case histories, and in vivo and in vitro studies showing coffee's potential to impair thyroxine (T4) intestinal absorption.


METHODS
Of eight women with inappropriately high or nonsuppressed thyroid-stimulating hormone (TSH) when T4 was swallowed with coffee/espresso, six consented to the evaluation of their T4 intestinal absorption. This in vivo test was also administered to nine volunteers. In three separate tests, two 100 microg T4 tablets were swallowed with coffee, water, or water followed, 60 minutes later, by coffee. Serum T4 was assayed over the 4-hour period of the test. Two patients and two volunteers also agreed on having tested the intestinal absorption of T4 swallowed with solubilized dietary fibers. In the in vitro studies, classical recovery tests on known concentrations of T4 were performed in the presence of saline, coffee, or known T4 sequestrants (dietary fibers, aluminium hydroxide, and sucralfate).


RESULTS
For the in vivo test, average and peak incremental rise of serum T4 (AIRST4 and PIRST4), time of maximal incremental rise of serum T4 (TMIRST4), and area under the curve (AUC) were determined. In patients and volunteers, the four outcome measures were similar in the water and water + coffee tests. In patients and volunteers, compared to water, coffee lowered AIRST4 (by 36% and 29%), PIRST4 (by 30% and 19%), and AUC (by 36% and 27%) and delayed TMIRST4 (by 38 and 43 minutes); bran was a superior interferer. In the in vitro studies, coffee was weaker than known T4 sequestrants.


CONCLUSIONS
Coffee should be added to the list of interferers of T4 intestinal absorption, and T4 to the list of compounds whose absorption is affected by coffee.
Benvenga
Salvatore
S
Sezione di Endocrinologia del Dipartimento Clinico Sperimentale di Medicina e Farmacologia, Università di Messina, Messina, Italy. s.benvenga@me.nettuno.it
Bartolone
Luigi
L
Pappalardo
Maria Angela
MA
Russo
Antonia
A
Lapa
Daniela
D
Giorgianni
Grazia
G
Saraceno
Giovanna
G
Trimarchi
Francesco
F
D000328:Adult; D000536:Aluminum Hydroxide / Q000008:administration & dosage / Q000009:adverse effects; D000863:Antacids / Q000008:administration & dosage / Q000009:adverse effects; D000897:Anti-Ulcer Agents / Q000008:administration & dosage / Q000009:adverse effects; D003069:Coffee / Q000009:adverse effects*; D004043:Dietary Fiber / Q000008:administration & dosage / Q000009:adverse effects; D004326:Drinking; D004347:Drug Interactions; D005260:Female; D006801:Humans; D007037:Hypothyroidism / Q000188:drug therapy*; D066298:In Vitro Techniques; D007408:Intestinal Absorption / Q000187:drug effects*; D008297:Male; D008875:Middle Aged; D012965:Sodium Chloride / Q000008:administration & dosage / Q000009:adverse effects; D013392:Sucralfate / Q000008:administration & dosage / Q000009:adverse effects; D013974:Thyroxine / Q000097:blood / Q000493:pharmacokinetics*
D000863:Antacids; D000897:Anti-Ulcer Agents; D003069:Coffee; D004043:Dietary Fiber; D012965:Sodium Chloride; D013392:Sucralfate; D000536:Aluminum Hydroxide; D013974:Thyroxine