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

Context:

An increased need for T₄ has been described in patients with different gastrointestinal disorders. However, there is a lack of systematic studies assessing the need for T₄ in hypothyroid patients with lactose intolerance, a widespread and often occult disorder.

Objective:

The objective of the study was to assess the replacement T₄ 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 T₄ 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 T₄ 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 T₄ dose of 1.31 μg/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 T₄ dose (1.29 μg/kg/d). In the remaining 29 patients, the T₄ dose was progressively increased and the target TSH (median TSH 1.21 mU/L) was attained at a median T₄ dose of 1.81 μg/kg/d (+38%, P < .0001). In six of these patients, other gastrointestinal disorders were diagnosed, and their median T₄ requirement was higher (2.04 μg/kg/d; +55%; P = .0032). In the remaining 23 patients with isolated lactose intolerance, a median T₄ dose of 1.72 μg/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 T₄ in hypothyroid patients.