Ramadan fasting and thyroid function: a narrative review of physiological adaptation and clinical management

Ramadan fasting may influence thyroid hormone homeostasis through changes in meal timing, circadian rhythm, and medication adherence. Its clinical impact appears to vary according to baseline thyroid status. This narrative review summarized the available evidence on the effect of Ramadan fasting on thyroid function among healthy, hypothyroid, and hyperthyroid individuals. A structured narrative review of the literature was conducted using PubMed/MEDLINE and Google Scholar from database inception to 2 July 2026. Original research, prospective and retrospective cohort studies, randomized clinical trials, systematic reviews, and relevant clinical guidance documents assessing thyroid function before, during, or after Ramadan were included. Evidence was organized according to thyroid status to facilitate clinical interpretation. Pooled evidence indicates that Ramadan fasting preserves hypothalamic-pituitary-thyroid (HPT) axis function within normal physiological reference ranges in healthy adults. In hypothyroid patients receiving levothyroxine, an increase in post-Ramadan TSH has been observed in several studies, although the contribution of fasting itself versus changes in medication timing, sleep, and circadian patterns remains uncertain; FT4 usually remained stable, and the biochemical change was more evident in patients with higher baseline TSH or poorer control. No single levothyroxine timing regimen consistently outperformed others, although adherence and patient preference were important determinants. In hyperthyroid patients, direct evidence is limited and recommendations are primarily based on expert opinion; fasting may be considered on an individualized basis in clinically stable patients with well-controlled disease, whereas active thyrotoxicosis warrants caution and individualized assessment. Ramadan fasting is usually safe from a thyroid perspective in healthy individuals and most stable hypothyroid patients, but biochemical monitoring and individualized counseling are recommended. Controlled studies in hyperthyroidism and trials evaluating alternative levothyroxine regimens are needed.