Letter to Editor about hypothyroidism and Ramadan fasting

Hadjazdeh et al. have reviewed literature regarding hypothyroidism and Ramadan fasting and conclude that fasting can change serum concentrations of thyroid hormones and TSH in both animals and humans (1). They also indicate that fasted hypothyroid individuals may suffer from thyroid hormone changes and therefore recommend that hypothyroid patients should increase their dosage of levothyroxine by 25-50 μg daily. We and others have shown that in experimental studies fasting is associated with a decrease in serum T3 and an increase in serum rT3. At least part of the reduction in serum T3 is due to a decrease in the peripheral conversion of T4 to T3. It has been shown that serum T3 and rT3 return to prefasting values upon refeeding with a mixed diet (2-4). We have also found that refeeding with a mixed diet or with carbohydrate, even though hypocaloric, reverses the changes in serum T3 and rT3 caused by fasting. This finding complements those of other studies that demonstrate the importance of dietarycarbohydrate in the modulation of serum T3 (5). Alteration in various parameters during Islamic (Ramadan) fasting is completely different from experimental fasting. From a physiological standpoint, Islamic fasting provides a unique model of intermittent daily fasting for one month. It is also distinct from regular voluntary or experimental fasting in that the faster does not drink during fasting hours. Therefore, one may assume that physiological changes occurring during Islamic fasting would differ from those observed during an experimental fast (6).