Iodine concentration of fortified and unfortified plant-based alternatives to milk, dairy products, eggs and fish
Authors: Bath S. C. , Nicol K. , Soutter L. , Benny B. , Yilmaz D. Y , GoenagaInfante H. , Hill S. , Rayman M. P. 
Published: December 2024

Animal foods, especially dairy products, eggs and fish, are the main source of iodine in the UK. However, the use of plant-based alternative products (PBAP) is increasing owing to issues of environmental sustainability. We previously measured the iodine content of milk-alternatives(1) but data are lacking on the iodine content of other plant-based products and there is now a greater number of iodine-fortified products. We aimed to compare: (i) the iodine concentration of fortified and unfortified PBAP and (ii) the iodine concentration of PBAP with their animal-product equivalents, including those not previously measured such as egg and fish alternatives.

The iodine concentration of 50 PBAP was analysed in March 2022 at LGC using ICP-MS. The products were selected from a market survey of six UK supermarkets in December 2021. Samples of matrix-matched (e.g. soya/oat) fortified and unfortified alternatives to milk (n = 13 and n = 11), yoghurt (n = 2 and n = 7) and cream (n = 1 and n = 5) were selected for analysis, as well as egg- (n = 1) and fish-alternatives (n = 10). We compared the iodine concentration between PBAPs and data on their animal-product equivalents(2).

The iodine concentration of fortified PBAPs was significantly higher than that of unfortified products; the median iodine concentration of fortified vs. unfortified milk alternatives was 321 vs. 0.84 µg/kg (p<0.001) and of fortified and unfortified yoghurt alternatives was 212 µg/kg vs 3.03 µg/kg (p = 0.04). The fortified cream alternative had a higher iodine concentration than the unfortified alternatives (259 vs. 26.5 µg/kg). The measured iodine concentration of the fortified products differed from that of the product label (both lower and higher); overall, the measured iodine concentration was significantly higher than that stated on the label (mean difference 49.1 µg/kg; p = 0.018).

Compared to the animal-product equivalents, the iodine concentration of unfortified PBAPs was significantly lower for milk (p<0.001) and yoghurt (p<0.001), while there was no difference with fortified versions of milk (p = 0.28) and yoghurt (p = 0.09). The egg alternative had an iodine concentration that was just 0.6% of that of chicken eggs (3.38 vs. 560 µg/kg). Three (30%) of the fish alternatives had kelp/seaweed as ingredients and the median iodine concentration of these products was (non-significantly) higher than those without (126 vs 75 μg/kg; p = 0.83). However, the iodine content of all fish-alternative products was ten-times lower than that of fish (median 99 vs. 995 µg/kg; p<0.001).

The majority of PBAP are not fortified with iodine but those that are fortified have a significantly higher iodine concentration than unfortified products and are closer to the value of their animal equivalents. From an iodine perspective, unfortified plant-based alternatives are not suitable replacements and consumers should ensure adequate iodine from other dietary sources. Manufacturers should consider iodine fortification of a greater number of plant-based alternatives.