New research from the National Institute for Health Research Bristol Biomedical Research Centre (NIHR Bristol BRC) says there is no evidence that recommending a low iodine diet for patients two weeks prior to treatment for differentiated thyroid cancer (DTC) as opposed to one week improves treatment success rates.

The most effective treatment for thyroid cancer is to surgically remove the thyroid and then use radioactive iodine to remove any residual thyroid or cancerous material. The UK clinical guidelines for this treatment advises patients should follow a low iodine diet for one to two weeks before radioiodine treatment to reduce the levels of iodine in their system. No hospitals in the UK measure iodine status before radioiodine treatment for thyroid cancer but hospitals do give different advice regarding low iodine diets.

Through previous qualitative research, the team understand that the diet is not straightforward and can cause stress to patients. This prior work also uncovered that explaining the diet takes up clinical time, so it is important to find out if it is necessary.

To see if there was a difference in success rates between one and two weeks the team analysed historic clinical data from three hospital trusts in the UK. Each hospital gave different advice regarding iodine restriction before radioiodine treatment. One trust advised two-week restriction, another hospital one week and a third did not advise the diet at all.

There were unanticipated differences in assessing outcomes at the time so they couldn’t compare the hospital that did not give advice with the other two. The study found no evidence that advising a low iodine diet for two weeks conferred any advantage over one week or evidence that this improves success rates.

Dr Clare England, Senior Research Associate and Research Dietitian on the NIHR Bristol BRC Nutrition Theme, who led the study said:

“This study still hasn’t been able to answer the main question as to whether it is important for patients with thyroid cancer to reduce their iodine status before radioiodine treatment.

“Routinely collected clinical data can’t answer this question and so we need a trial or a carefully designed observational study that measures iodine status.”

Paper: Low iodine diet advice and differentiated thyroid cancer treatment: a historic exploration in three UK centres Clare England et al, Clinical Nutrition ESPEN