Impact of Low Iodine Diets on Ablation Success in Differentiated Thyroid Cancer

A Mixed-Methods Systematic Review and Meta-Analysis

Georgia Herbert; Clare England; Rachel Perry; Alex Whitmarsh; Theresa Moore; Aidan Searle; Sneha Chotaliya; Andy Ness; Matthew Beasley; Charlotte Atkinson


Clin Endocrinol. 2022;97(6):702-729. 

In This Article

Abstract and Introduction


Background: Debate remains regarding whether to recommend a low iodine diet (LID) before radioactive-iodine treatment and its duration and stringency. This mixed-methods review aimed to determine if iodine status affects treatment success, the most effective diet to reduce iodine status, and how LID impacts wellbeing.

Methods: Five electronic databases were searched until February 2021. An effectiveness synthesis (quantitative studies) and views synthesis (qualitative, survey, and experience-based evidence) were conducted individually and then integrated. Quality assessment was undertaken.

Results: Fifty-six quantitative and three qualitative studies were identified. There was greater ablation success for those with an iodine status of <50 mcg/L (or mcg/gCr) compared with ≥250 (odds ratio [OR] = 2.63, 95% confidence interval [CI], 1.18–5.86, n = 283, GRADE certainty of evidence very low). One study compared <50 mcg/L (or mcg/gCr) to 100–199 and showed similar rates of ablation success (OR = 1.59, 95% CI, 0.48–6.15, n = 113; moderate risk of bias). People following a stricter LID before ablation had similar rates of success to a less-strict diet (OR = 0.67, 95% CI, 0.26–1.73, n = 256, GRADE certainty of evidence very low). A stricter LID reduced iodine status more than a less strict (SMD = −0.40, 95% CI, −0.56 to −0.24, n = 816), and reduction was seen after 1 and 2 weeks. The main challenges were a negative impact on psychological health, over restriction, confusion, and difficulty for sub-groups.

Conclusions: Although a LID of 1–2 weeks reduces iodine status, it remains unclear whether iodine status affects treatment success as only a few low-quality studies have examined this. LIDs are challenging for patients. Higher-quality studies are needed to confirm whether a LID is necessary.


Differentiated thyroid cancer (DTC) is usually treated with total thyroidectomy, followed by radioactive-iodine treatment (RAIT) with 131I to destroy any residual thyroid tissue or cancerous tissue left postsurgery (ablation). After ablation, radio-iodine can also be used to treat residual, recurrent or metastatic disease (therapy).[1] Thyroid-stimulating hormone should be raised to facilitate uptake of 131I. It has been suggested that high iodine status may interfere with RAIT efficacy as nonradioactive iodine competes with 131I for uptake by the thyroid.[2] Furthermore, depleting plasma iodide concentrations may increase the expression of the sodium–iodine symporter gene, increasing the amount of radioactive-iodine uptake in remnant thyroid tissue or DTC cells.[3] Many international guidelines on the management of thyroid cancer suggest reducing iodine status before RAIT using low iodine diets (LID).[1,4,5] However, the available evidence for benefit of low iodine status on the efficacy of RAIT for DTC is weak.[6,7] This has led to inconsistencies both within and between countries regarding recommendations for LID duration and target urinary iodine concentration. In 2015, the Italian Society of Endocrinology recommended that a LID before RAIT was not necessary in countries with mild to moderate iodine deficiency,[8] and was updated in 2018 to suggest avoiding preserved fish, sushi, and seaweed for 1–2 weeks before RAIT.[9] The iodine status of the UK falls into this mild to moderate bracket[10] but British Thyroid Association guidelines state that patients should be advised to follow a LID for 1–2 weeks before RAIT.[1] A recent survey of practice found that different treatment centres in the UK gave varying LID advice.[11]

Debate, therefore, remains not only as to whether to recommend a LID or not, but also the duration and stringency. Previous reviews[6,7] were limited in their searches (e.g., excluded non-English articles, restricted databases), analysis, and descriptions of study quality and additional studies may have been published since the last review in 2016. Furthermore, the impact of the LID on wellbeing has not previously been systematically reviewed. Short-term dietary interventions such as the LID may at first seem achievable but are burdensome.[12–14]

The aim of this review was to conduct the first mixed-method synthesis in people with DTC receiving RAIT after total thyroidectomy to yield maximum breadth and depth of understanding by addressing the following questions:

Effectiveness synthesis

1. What is the effect of iodine status or LID on ablation and therapy success?

2. What is the effect of iodine status on recurrence of thyroid cancer or cancer-related mortality?

3. What is the effect of LID advice on iodine status before RAIT or whole-body scan?

4. Are there any complications or adverse effects from consuming a LID?

Views synthesis

5. What are the facilitators and barriers of consuming a LID?