Effect of vitamin C on the absorption of levothyroxine in patients with hypothyroidism and gastritis.

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.