Effect of vitamin C on the absorption of levothyroxine in patients with hypothyroidism and gastritis
Abstract
BACKGROUND: Malabsorption of l-T4 is a major clinical problem. Changes in gastric pH caused by several medical illnesses are associated with difficulties in the control of patients with hypothyroidism receiving the hormone. Means to correct these alterations would be of clinical value. OBJECTIVES: Our objective was to study the effect of vitamin C on the absorption of l-T4 in patients with hypothyroidism and gastritis. DESIGN: Thirty-one patients with hypothyroidism, 28 females age 47.5 ± 13.5 (mean ± SD) years and 3 males age 55.7 ± 11.2 years ingested the dose of l-T4 in 120 mL water containing or not containing 500 mg vitamin C in a solution of pH 2.9 ± 0.1 (mean ± SD). Serum concentrations of free T4 and TSH were measured at the end of 3 periods of 2 months each, 2 controls and 1 vitamin C. Serum total T3 was measured in 16 of the patients, before and at the end of the vitamin C period. Serum TSH and free T4 and T3 were measured by a solid-phase, enzyme-labeled chemiluminescent competitive immunoassay All patients had gastrointestinal pathology and were not in good control when taking l-T4 before the study, and 23 had autoimmune thyroiditis or idiopathic hypothyroidism. The median l-T4 dose was 100 μg with an interquartile range of 50 μg. The protocol was reviewed and approved by our institution's ethics committee. Patients were asked to sign a written consent to participate in the study. RESULTS: Serum concentrations of TSH, free T4, and T3 improved while on vitamin C. Serum TSH decreased in all patients (control, 11.1 [10.5] μIU/mL, median [interquartile range]), vitamin C 4.2 (3.7) μIU/mL, P = .0001), and it was normalized in 17 patients (54.8%). The average decrease was 69.2%. Serum T4 was higher with vitamin C in 30 of the 31 patients (control, 1.1 [0.3] ng/dL; vitamin C, 1.3 [0.3] ng/dL; P < .0001), and serum T3 increased as well in all 16 patients in whom it was measured (control, 60.5 [16.5] ng/dL; vitamin C, 70 [21] ng/dL; P < .005). CONCLUSIONS: In patients with hypothyroidism and gastrointestinal pathology, vitamin C improves the abnormalities in serum free T4, T3, and TSH concentrations. This approach is helpful in the management of these patients.
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Vitamin C can improve LT4 absorption, presumably by providing an acidic gastric environment.
“It is interesting to note that vitamin C can improve LT4 absorption, presumably by providing an acidic gastric environment (50).”
From ETA guidelines for the use of levothyroxine sodium preparations in monotherapy to optimize the treatment of hypothyroidism (2025) · cites this paper as [50]
Vitamin C seems to increase the efficacy of LT4 absorption in a subset of hypothyroid patients with decreased gastric acidity.
“vitamin C seems to increase the efficacy of LT4 absorption in a subset of hypothyroid patients with decreased gastric acidity (50).”
From ETA guidelines for the use of levothyroxine sodium preparations in monotherapy to optimize the treatment of hypothyroidism (2025) · cites this paper as [50]
Vitamin C, which promotes the secretion of gastric acid, presents a potential option to ameliorate malabsorption.
“In contrast, vitamin C, which promotes the secretion of gastric acid, presents a potential option to ameliorate malabsorption (80).”
From Levothyroxine: conventional and novel drug delivery formulations. (2023) · cites this paper as [80]
Both 2-month-long trials with vitamin C lack formal pharmacokinetics studies and challenge of patients with IM-associated undertreated hypothyroidism.
“Both 2-month-long trials with vitamin C (115, 116) lack formal pharmacokinetics studies and challenge of patients with IM-associated UTH.”
From L-T4 therapy in the presence of pharmacological interferents (2020) · cites this paper as [116]
In the Colombian study, the 31 patients had endoscopy/gastritis-proven gastritis.
“in the Colombian study, the 31 patients had endoscopy/gastritis-proven gastritis (116).”
From L-T4 therapy in the presence of pharmacological interferents (2020) · cites this paper as [116]
Vitamin C co-administration may increase LT4 absorption, especially in patients with gastrointestinal issues.
“Co-administration with vitamin C may increase LT4 absorption, particularly, in patients with gastrointestinal issues.89,90”
From Refractory hypothyroidism: unraveling the complexities of diagnosis and management (2023) · cites this paper as [89]
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- Authors
- Jubiz, W., & Ramirez, M.
- Affiliations
- Universidad Libre (CO)
- Corresponding author
- Jubiz, William
- Venue
- The Journal of Clinical Endocrinology & Metabolism
- Publisher
- The Endocrine Society
- Published
- 2014-06-01
- Volume
- 99
- Issue
- 6
- Pages
- E1031-E1034
- ISSN
- 0021-972X (ISSN-L)
- 1945-7197
- OpenAlex
- W2091955947
- Cited by
- 45
- References
- 20
- Citations by year
- 2026: 1 · 2025: 3 · 2024: 2 · 2023: 7 · 2022: 5 · 2021: 5 · 2020: 4 · 2019: 2 · 2018: 6 · 2017: 4 · 2016: 1 · 2015: 2 · 2014: 2
- FWCI
- 2.41
- Type
- journal article
- Language
- en
- Open access
- closed
- Locations
- The Journal of Clinical Endocrinology & Metabolism (publishedVersion)
- PubMed (publishedVersion)
- Topics
- Health Sciences › Medicine › Endocrinology, Diabetes and Metabolism › Thyroid Disorders and Treatments
- Health Sciences › Nursing › Nutrition and Dietetics › Vitamin C and Antioxidants Research
- Health Sciences › Medicine › Surgery › Thyroid and Parathyroid Surgery
- Keywords
- vitamin C, levothyroxine, hypothyroidism, gastritis, drug absorption, gastric pH, thyroid-stimulating hormone, free thyroxine, triiodothyronine, autoimmune thyroiditis, malabsorption, thyroid hormone replacement, T3/T4 ratio, TSH suppression, TSH receptor antibodies
- MeSH terms
- Adult, Aged, Ascorbic Acid, Female, Gastritis, Humans, Hypothyroidism, Intestinal Absorption, Male, Middle Aged, Thyroid Function Tests, Thyrotropin, Thyroxine, Triiodothyronine
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