A new British study warns that swapping dairy for plant-based alternatives could trigger serious iodine deficiencies and thyroid complications.
Researchers from the University of Surrey and Queen’s University Belfast analyzed nutritional data from 3,500 participants in the National Diet and Nutrition Survey alongside 164 non-dairy milks, 76 yoghurts and 67 cheese alternatives, publishing their findings in The Lancet Planetary Health journal. The scale of the gap stunned them: only 16 of those hundreds of products were fortified with iodine, an essential compound that regulates metabolism, thyroid hormones and brain function.
Dr Sarah Bath, the study’s lead author, highlighted Britain’s particular vulnerability to this shortfall. “The UK is particularly vulnerable to iodine insufficiency due to a lack of an iodine fortification policy such as universal salt iodisation, which many other countries have,” she said. “But many people are unaware of the importance of iodine – and the fact that dairy products are one of its richest dietary sources in the UK.”
The findings carry sharp consequences for anyone reducing dairy intake. Replacing just 20 to 35 per cent of dairy products with plant-based alternatives significantly increased iodine inadequacy among women and girls, the researchers found. Calcium intake also dropped sharply for both girls and boys making the switch.
Bath drove home the practical risk for consumers already filling their carts with oat, almond, coconut and soya options. “Unless fortified, plant-based alternatives contain very little iodine – and this could cause problems for some people,” she said.
The study revealed uneven fortification patterns across the alternative dairy aisle. While 61 per cent of milks contained added calcium and 46 per cent included vitamin B12, just one in five were fortified with riboflavin. The iodine numbers lagged far behind all of these.
Iodine deficiency carries recognizable and potentially severe symptoms. Adults who fall below the recommended 150 micrograms daily can develop a thyroid goitre, a visible neck lump stemming from thyroid complications. Fatigue, weight gain, dry skin, constipation, difficulty concentrating and hair loss signal a stressed thyroid. Excess iodine triggers the inverse: anxiety and weight loss from hormone overproduction.
The researchers drew their conclusions from one of the largest combined analyses of dietary survey data and product composition in this category to date. Their work arrives as plant-based milks have proliferated far beyond the soy and rice options of earlier decades, with oat and almond varieties now dominating café menus and home refrigerators alike.
For those seeking iodine outside dairy, smaller amounts appear in fish, yogurt, pink salt and seaweed. Yet none of these match the concentrated, consistent delivery that fortified dairy or systematically enriched alternatives could provide.
The study lands amid a broader shift in British eating habits that has seen vegan and lactose-free choices surge from niche alternatives to mainstream staples. What began as a limited market of soy and rice milks has ballooned into shelves crowded with oat, coconut, hazelnut and blended options marketed for health and environmental benefits.
The researchers did not call for abandoning plant-based diets but instead spotlighted the need for better fortification standards and consumer awareness about what those products actually contain.