Does coffee interfere with synthetic hormones used for treatment of hypothyroidism?
Although not specifically stated in the labeling for levothyroxine (L-T4), in clinical practice guidelines, coffee is recognized as a compound that may interact with this synthetic hormone used in the treatment of primary or central hypothyroidism.
A recent case published in the Journal of the Academy of Nutrition and Dietetics, reports on this interaction in a patient on L-T4 with uncontrolled hypothyroidism likely linked to concurrent consumption of American coffee.
The patient, a 52-year old white woman, presented to a primary care clinic for a regular check-up and to review her type 2 diabetes treatment plan; her medical history included primary hypothyroidism caused by Hashimoto's thyroiditis, type 2 diabetes mellitus, primary hypertension and morbid obesity. Her list of medicines included:
— Amlodipine 10mg once daily
— Aspirin 81mg once daily
— Atorvastatin 20mg once daily
— Long-acting basal insulin (varied doses) SC at bedtime
— Levothyroxine 175mcg once daily
— Lisinopril 20mg once daily
— Metformin 1000mg twice daily
Mental Health Update | All medications were taken for at least two years, except for atorvastatin which was started a month earlier; and the patient appeared adherent to her drug regimen. She denied using any over-the-counter drugs, vitamins or dietary/herbal supplements; she was not a smoker and denied alcohol and illicit drug use.
During the visit, it was observed that the patient had gained 15.2lbs over a 6-week time period but denied other symptoms such as fatigue, constipation, cold intolerance, dry skin, changes in mood or myalgias, all symptoms related to hypothyroidism. A measurement of serum thyroid-stimulating hormone (TSH) during this visit showed it to be 8.270mU/L; her previous level taken 14 months prior was 1.65mU/L.
After interviewing the patient, it was discovered that she routinely ingested her L-T4 with a cup of coffee. Previously, her coffee intake had been sporadic, until 2 months prior when she started preparing American coffee (drip coffee with creamer and sugar) at home and drinking 10–12 oz daily while taking her L-T4 pill at the same time; breakfast was then consumed 45–60 minutes after the dose.
To test the possibility of an interaction, the patient was told to take the L-T4 pill on an empty stomach and not drink coffee for at least an hour after consuming her medication. Six weeks later, the patient's TSH level was 0.24mU/L, below the desired range (reference range: 0.45–4.5mU/L), indicating that the dose of L-T4 was now too high. The dose was then reduced to 150mcg once daily.
Using the Naranjo Algorithm, clinicians interpreted the drug interaction as "probable" (Naranjo score: 6), for possible interaction with the creamer or sugar.
But given that previous evidence of coffee-L-T4 interaction exists, using the Drug Interaction Probability Score, the interaction with coffee scored a 9, indicating it was "highly probable" that coffee was the likely instigator, especially since the only change made during the two visits was that coffee was consumed 60 minutes after administration of L-T4 dose.
- While these tools help to predict causality, it should be noted that they cannot prove causality. However, based on the evidence, it was determined that the patient’s non-suppressed TSH was caused by the concurrent ingestion of L-T4 and American coffee.
Coffee is a mixture of many substances and nutriceuticals, and its chemical composition is determined by many factors (ie, roasting, grinding, extraction). Previous reports of coffee interaction with L-T4 have only involved Italian coffee (ie, espresso), this is the first known case of an interaction with American coffee. The specific compound which binds L-T4 and makes it less available for intestinal absorption is unknown, however, lipid sequestration may be a possible mechanism, as lipid content makes up 15–17% of arabica coffee and 10–11.5% of robusta coffee.
The increase in TSH, which occurred during routine coffee consumption, and then the subsequent decrease in TSH after cessation of coffee and concomitant L-T4 indicates that in this case, it is likely that coffee was the compound that caused the interaction; there are no known drug interactions with the patient's other medications. Also, no known interactions have been reported with caffeine, creamer, or sugar.
Coffee effects | It is also important to note that increasing the dose of L-T4 in this patient may have caused harm in the future had the patient ceased drinking coffee with her medication, indicating the importance of assessing coffee consumption in a patient taking L-T4, especially in patients with nonsuppressed TSH.
The authors conclude by stating; “coffee should be uniformly added to the list of compounds that may decrease L-T4 absorption across drug compendia."
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