Systematic Appraisal of Lactose Intolerance as Cause of Increased Need for Oral Thyroxine

Context: An increased need for T-4 has been described in patients with different gastrointestinal disorders. However, there is a lack of systematic studies assessing the need for T-4 in hypothyroid patients with lactose intolerance, a widespread and often occult disorder. Objective: The objective of the study was to assess the replacement T-4 dose required in hypothyroid patients with lactose intolerance. Design: This was a cohort study. Setting: The study was conducted at an outpatient endocrinology unit in a University Hospital. Patients: The replacement T-4 dose has been analyzed, from 2009 to 2012, in 34 hypothyroid patients due to Hashimoto's thyroiditis and lactose intolerance and being noncompliant with a lactose-free diet. Main Outcome Measure: An individually tailored T-4 dose was measured. Results: In all patients with isolated Hashimoto's thyroiditis, target TSH (median TSH 1.02 mU/L) was obtained at a median T-4 dose of 1.31 mu g/kg/d. In patients with lactose intolerance, only five of 34 patients reached the desired TSH (median TSH 0.83 mU/L) with a similar T-4 dose (1.29 mu g/kg/d). In the remaining 29 patients, the T-4 dose was progressively increased and the target TSH (median TSH 1.21 mU/L) was attained at a median T-4 dose of 1.81 mu g/kg/d (+38%, P < .0001). In six of these patients, other gastrointestinal disorders were diagnosed, and their median T-4 requirement was higher (2.04 mu g/kg/d; +55%; P = .0032). In the remaining 23 patients with isolated lactose intolerance, a median T-4 dose of 1.72 mu g/kg/d (+31% P < .0001) has been required to attain pharmacological thyroid homeostasis. Conclusions: These findings show that lactose intolerance significantly increased the need for oral T-4 in hypothyroid patients.