Can desalinated seawater contribute to iodine-deficiency disorders? An observation and hypothesis

Abstract

Objective: Over 300 million people rely on desalinated seawater and the numbers are growing. Desalination removes iodine from water and could increase the risk of iodine-deficiency disorders (IDD). The present study assessed the relationship between iodine intake and thyroid function in an area reliant on desalination.

Design: A case-control study was performed between March 2012 and March 2014. Thyroid function was rigorously assessed by clinical examination, ultrasound and blood tests, including serum thyroglobulin (Tg) and autoimmune antibodies. Iodine intake and the contribution made by unfiltered tap water were estimated by FFQ. The contribution of drinking-water to iodine intake was modelled using three iodine concentrations: likely, worst-case and best-case scenario.

Setting: The setting for the study was a hospital located on the southern Israeli Mediterranean coast.

Subjects: Adult volunteers (n 102), 21-80 years old, prospectively recruited.

Results: After screening, seventy-four participants met the inclusion criteria. Thirty-seven were euthyroid controls. Among those with thyroid dysfunction, twenty-nine were classified with non-autoimmune thyroid disease (NATD) after excluding eight cases with autoimmunity. Seventy per cent of all participants had iodine intake below the Estimated Average Requirement (EAR) of 95 µg/d. Participants with NATD were significantly more likely to have probable IDD with intake below the EAR (OR=5·2; 95 % CI 1·8, 15·2) and abnormal serum Tg>40 ng/ml (OR=5·8; 95 % CI 1·6, 20·8).

Conclusions: Evidence of prevalent probable IDD in a population reliant on desalinated seawater supports the urgent need to probe the impact of desalinated water on thyroid health in Israel and elsewhere.

Keywords: Iodine-deficiency disorders; Seawater reverse-osmosis desalination; Semi-quantitative iodine FFQ; Thyroglobulin.

Fig. 1

Models for the distribution of estimated daily iodine intakes according to likely, best- and worst-case assumptions of water iodine content. The distribution of the study population’s iodine intake (µg/d) from the sIFFQ (n 74) estimated assuming three different iodine concentrations for tap water: (a) likely, 27 µg/l; (b) worst-case scenario using only iodine content in SWRO desalinated water, 1 µg/l; (c) best-case scenario based on the highest local iodine content measured in well water, 170 µg/l. ——— indicates Weibull fit; – – – – – indicates RDA reference line (150 μg/d) (sIFFQ, semi-quantitative iodine FFQ; SWRO, seawater reverse osmosis)