The Influence of Health Literacy on the Control of Hypothyroidism in Patients Under Levothyroxine Treatment.

OBJECTIVE: To investigate the association between health literacy levels and biochemical control of hypothyroidism, measured by serum TSH and free thyroxine (FT4) levels, in patients receiving levothyroxine (L-T4) therapy. METHODS: We conducted a cross-sectional study at the Thyroid Disorders Outpatient Clinic, Escola Paulista de Medicina, Universidade Federal de São Paulo (EPM/UNIFESP), between April and December 2024. The protocol was approved by the institutional ethics committee (CAAE: 76540423.5.0000.5505), and all participants provided written informed consent. Adult patients aged 18-65 years with primary hypothyroidism on levothyroxine (L-T4) therapy were screened; 274 met eligibility criteria after exclusions. Health literacy was assessed using the Brazilian-Portuguese Newest Vital Sign (NVS), administered face-to-face by trained staff. Demographic and clinical data, including comorbidities, L-T4 dose, TSH, and FT4 levels, were extracted from electronic records. Biochemical analyses were performed using electrochemiluminescence immunoassays. Statistical analyses included ANOVA, χ² tests, and generalised linear regression, with significance set at p < 0.05. RESULTS: Among 274 patients included in the final analysis, health literacy was inversely associated with serum TSH levels, and this association remained significant in fully adjusted models. A marginal trend was observed for FT4, but it did not reach statistical significance after adjustment. Patients with lower literacy scores required higher levothyroxine doses per kilogram, suggesting less efficient treatment control. No significant differences in comorbidities were observed across literacy strata. CONCLUSIONS: Limited health literacy was independently associated with poorer biochemical control of hypothyroidism, reflected by higher TSH concentrations and greater levothyroxine dose requirements. These findings reinforce health literacy as a modifiable determinant of treatment success. Incorporating literacy-sensitive strategies-such as plain-language counselling, teach-back techniques, and visual aids-into routine care may help stabilise TSH, optimise levothyroxine therapy, and improve long-term outcomes in this population.