Abstract
Celiac disease can significantly impair levothyroxine absorption, complicating hypothyroidism management despite appropriate dosing. While a gluten-free diet often improves absorption, some patients continue to require high doses. Switching to liquid or softgel formulations can enhance levothyroxine bioavailability and symptom control. Optimizing therapy requires individualized approaches, including dietary intervention, formulation changes, and close monitoring, to achieve and maintain a euthyroid state. Relevant studies were reviewed and incorporated into this commentary to support evidence-based recommendations and highlight clinical considerations.
Celiac disease (CD) is a chronic, immune-mediated enteropathy of the small intestine triggered by gluten in genetically predisposed individuals. Gluten exposure leads to mucosal inflammation, villous atrophy, and crypt hyperplasia, compromising intestinal integrity, and increasing immune sensitivity to gluten. Celiac disease is characterized by gastrointestinal symptoms including diarrhea, abdominal discomfort, weight loss, anemia, osteoporosis, and liver damage. The cornerstone of treatment is a strict gluten-free diet, supplemented with vitamins and minerals to address common deficiencies. 1 Conditions such as thyroid disorders, type 1 diabetes, and multiple sclerosis are associated with a higher likelihood of CD.2,3
Celiac disease significantly alters gastrointestinal function, affecting drug absorption due to changes in gastric emptying, increases in intraluminal pH, and reduction in intestinal surface from villous atrophy. These disruptions impair the bioavailability of medications including levothyroxine, which has a narrow therapeutic index. Levothyroxine absorption is further reduced by interactions with food and co-administered medications, such as calcium and iron, which can chelate the drug. 4 Elevated levothyroxine requirements may signal undiagnosed CD, supporting the recommendation for targeted serologic screening in hypothyroid patients with increased dosing needs (levothyroxine ≥ 125 µg/day). 5 In addition, CD is associated with impaired enzymatic activity, such as reduced intestinal cytochrome P450 enzymes, and increased gut permeability further influencing drug metabolism and absorption.6-8
An expert consensus supports the recognition and management of CD in hypothyroid patients with levothyroxine resistance. This includes dietary modifications, such as a gluten-free diet and switching to better-absorbed dosage formulations. 9 We conducted a literature search and a bibliographic search of references using the terms levothyroxine, hypothyroidism, celiac disease, malabsorption, and dosage forms. Studies were included based on their focus on the impact of celiac disease-related malabsorption on levothyroxine and strategies for mitigating malabsorption and optimizing thyroid hormone therapy.
Dietary Modifications
In a retrospective study, the impact of CD on levothyroxine dosing in patients with concomitant hypothyroidism was investigated. Among 152 patients with biopsy-confirmed CD, 22 (14.5%) also had hypothyroidism. Of these, seven met inclusion criteria for analysis, having no prior intestinal surgery and adequate dosing data. These patients required significantly higher doses of levothyroxine compared with 200 control patients with hypothyroidism alone (154 µg ± SD 65 vs 106 µg ± SD 46; P = 0.007). Following initiation of a gluten-free diet in six patients, the mean levothyroxine requirement significantly decreased by 43 µg/day (P = 0.03) and was no longer significantly different from controls (111 µg vs 106 µg; P = 0.79). These findings support the hypothesis that untreated CD leads to levothyroxine malabsorption and that a gluten-free diet can improve levothyroxine absorption, reducing the need for higher doses. 10
Alternate Dosage Forms
Levothyroxine capsules and oral solution are formulated with minimal excipients, making them ideal for patients with sensitivities. Unlike traditional levothyroxine tablets that may contain gluten, lactose, or dyes, which can interfere with absorption, especially in individuals with CD, liquid formulations bypass the need for gastric dissolution, providing more consistent and reliable absorption. This can be particularly beneficial in patients with persistent malabsorption. 11 Several case reports and case series highlight a consistent trend of hypothyroid patients with underlying gastrointestinal disorders, particularly CD, experiencing poor response to standard levothyroxine tablets despite adherence. These patients were typically on levothyroxine doses ranging from 100 to 200 µg daily yet continued to have elevated thyroid stimulating hormone (TSH) levels and low or unreported T4 levels, indicating persistent hypothyroidism. Multi-modal management strategies to achieve euthyroid status included initiating a gluten-free diet, switching and adjusting dosing regimens to alternate formulations such as an oral solution. Following these adjustments, all patients became euthyroid. The normalization of TSH levels suggests that malabsorption is a critical factor in levothyroxine resistance and that non-tablet formulations and dietary modifications can significantly improve thyroid hormone bioavailability in patients with gastrointestinal comorbidities.12-15
In patients with absorption challenges including CD, hypothyroidism may persist despite strict adherence to a gluten-free diet, likely due to ongoing malabsorption. When thyroid hormone levels remain suboptimal, switching to alternative levothyroxine formulations such as parenteral, liquid or softgel capsules can improve outcomes.16,17 The CONTROL Switch Study, a retrospective chart review, evaluated the effects of switching 99 uncontrolled hypothyroid patients from levothyroxine tablets to gel capsules, six of whom had CD. Overall, following the switch, 26.3% showed improvement in TSH levels, 51.5% experienced no change, and 22.2% had worsening TSH levels. The average number of dose adjustments decreased significantly by 54.7% from 1.61 pre-switch to 0.73 post-switch per patient (P < 0.0001). Furthermore, 61.6% of patients reported improved hypothyroid symptom control, while only 8.1% noted worsening symptoms (P < 0.0001). Among patients with CD, 83.3% (5/6) reported symptom improvement, along with a reduction in dose adjustments. Overall, these findings underscore improved absorption and enhanced tolerability of gel capsules, particularly in patients with absorption-related issues or intolerance to traditional tablets. The study’s limitations include its retrospective design, manufacturer funding, and limited inclusion of CD patients. The effect on TSH was only reported in the full cohort, not CD patients specifically, therefore further studies should be conducted in CD. 16
Other Strategies
Co-administration with vitamin C lowers gastric pH to further improve dissolution and subsequent absorption of levothyroxine, particularly in patients with gastrointestinal conditions.17-19
Conclusion
Celiac disease can impair levothyroxine absorption, complicating the management of hypothyroidism despite adherence to therapy. The current literature is limited to retrospective reviews and case reports, with a lack of randomized clinical trials. More robust, well-designed studies are needed to understand the optimal management strategies in this population. Despite limited data, some practical measures may help guide management. While a gluten-free diet improves absorption and reduces higher dosing needs, some patients continue to experience inadequate control. In such cases, switching to liquid or softgel may improve bioavailability and symptom control. In addition, ensuring levothyroxine is taken 30 to 60 minutes before the first meal of the day is essential for optimal absorption. An unusually high levothyroxine dose may serve as a clinical clue, warranting screening for CD. Ultimately, individualized treatment approaches that include dietary intervention, formulation selection, and patient-specific dosing are essential to achieving euthyroid status in this unique population.
Footnotes
Funding
The authors received no financial support for the research, authorship, and/or publication of this article.
Declaration of Conflicting Interests
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.