Is a strict restricted-iodine diet necessary for preparation of radioactive iodine therapy?

A restricted-iodine diet (RID) increases the effectiveness of radioiodine therapy (RAIT) by decreasing the body's iodine pool, especially in iodine-rich regions. However, there is no consensus on the RID that should be applied in iodine-deficient areas. This study aims to assess the effect of strict and flexible RID before RAIT.

For the study, 144 patients were randomized into the strict or flexible RID group. All patients stopped levothyroxine before RAIT and followed a RID. After 2 weeks of RID, 24-h urine samples were taken. The urinary iodine excretion was compared. In 52 of 144 patients, the spot urine samples were taken before and after RID. The reduction in urinary iodine excretion was compared according to the iodine/creatinine ratio.

Our study included 47 males and 97 females with a mean age of 45 years. After RID in the 24-h urine samples, the mean iodine level was 47.9 µg/day, and both protocols were sufficient to reduce the body iodine pool. There was no significant difference between the strict and the flexible group, 43.06 and 52.89 µg/day (P:0.147). The reduction in urinary iodine excretion was not statistically different in both groups according to spot urine samples (68.20 vs. 60.53%; P:0.377).

The flexible RID protocol that less disrupts the patient's quality of life can be preferred for RAIT preparation in iodine-deficient countries.