Will Plant-Based Milk Iodine Fortification Ever Be Enough for Teenage Girls?

Britain has put calcium, iron, thiamine and niacin into its white flour since the 1940s, and folic acid more recently, yet it never iodised its salt. A study published this week in The Lancet Planetary Health modelled what happens to iodine intake when dairy consumption falls in a country with no iodine policy of its own. Researchers at the University of Surrey and Queen’s University Belfast ran the numbers. The survey covered 3,558 people. The shelves held 289 plant-based products.

Replacing 35 percent of dairy products with plant-based alternatives, at today’s fortification levels, cut average iodine intake by 9 to 21 percent. Inadequate intake among girls aged 14 to 18 rose from 54 percent to 65 percent, and among women aged 19 to 49 from 32 percent to 42 percent. At full replacement, the model put 80 percent of teenage girls and 72 percent of teenage boys below the requirement for iodine. Iodine feeds the thyroid. Its hormones regulate metabolism, growth and brain development.

Mandatory fortification of every plant-based alternative held average intakes flat at every level of replacement. The modelled level was 22.5 micrograms of iodine per 100 grams. Averages held. It still left 56 to 59 percent of teenage girls below the requirement at every replacement level, and 32 to 37 percent of women aged 19 to 49, because their intakes were already low before any swap began.

Replacing all the salt in commercially produced bread with iodised salt cut inadequate intake among teenage girls from 54 percent to 37 percent, before any dairy was replaced. The salt carried 30 milligrams of iodine per kilogram. The combined approach, fortified alternatives plus iodised bread, held girls at 37 percent when a fifth of dairy was replaced, and 43 percent at full replacement. For women aged 19 to 49, the combined approach cut inadequacy from 32 percent to 20 percent at a fifth replaced, and held it near 21 to 22 percent at higher replacement levels. Bread alone was less steady: at full replacement, inadequacy among women aged 19 to 49 climbed back to 44 percent.

More than half of teenage girls, 54 percent, already had inadequate iodine intake on their ordinary diets, with an average intake of 97 micrograms a day, the lowest of any group the researchers measured. Children get about half their iodine from dairy, and adults about a third. Dairy’s iodine in Britain is largely incidental. It arrives through iodine added to cattle feed for animal health, and through iodine-containing disinfectants used in dairy production. Salt was never iodised. Universal salt iodisation is the World Health Organization’s recommended strategy. It has eliminated an estimated 3.3 billion cases of inadequate intake worldwide. Britain simply never adopted it. Closing it would mean changing food production practices and public health messaging built around salt reduction.

Only 12 percent of the 289 plant-based products surveyed carried added iodine, against 61 percent with added calcium and 46 percent with added vitamin B12. Iodine fortification was virtually absent from plant-based cheeses and yoghurts. Only about a fifth of milk alternatives were fortified at all. An earlier survey of the same market found no cheese alternative fortified with iodine and only 5 percent of yoghurt alternatives, and three unfortified portions a day would cut the iodine those foods provide by almost 98 percent. The big brands already do most of what a mandate would require: Danone says its core Alpro range carries iodine, calcium, vitamins B2 and B12, and Oatly says its unflavoured, non-organic oat drinks are fortified with iodine among other nutrients. A rule would land hardest on the long tail of unfortified products and on the cheese and yoghurt shelves, not on the cartons most shoppers recognise.

On Threads, a British tea drinker who switched to oat milk years ago wrote, “I switched to oat milk a few years ago and now prefer it in my tea.” She settled on Alpro’s no-sugar version because oat milks vary in thickness by brand. On X, a woman who switched to almond milk as a little girl because her body was rejecting dairy wrote, “I switched to almond milk as a little girl. It was the best decision ever.” Neither chose by the nutrient label. In a Facebook group for people on a low-iodine diet, another shopper put the oat milk iodine question plainly: “Are there any oat milk brands which don’t contain iodine?” Fortify every carton. The first two shoppers lose nothing, since the brands they picked are already fortified, and the third loses the product she is looking for.

Folic acid fortification of flour was added by updated legislation, and Australia, New Zealand and the Netherlands already put iodised salt into bread, with the paper citing improvements in iodine status of 38 to 66 percent among children and adults there. Norway’s experience supplies the caution, with 8 to 18 percent of young children there exceeding the upper limit for iodine, while this study reports that iodised bread did not increase any subgroup’s share over the limit compared with baseline.

Plant-based milk iodine is the nutrient that moves first, but it isn’t the only one that falls. Calcium inadequacy already affected 54 percent of teenage girls before any swap, the same share as iodine, and average intakes of calcium, riboflavin and vitamin B12 also declined as replacement rose, though the share below the requirement for those three only rose at half or full replacement. Young children drink the most dairy. Boys aged one to three average 395 grams a day. They are the group for whom fortifying the alternatives helps most directly, the authors write.

The plant-based milk iodine numbers are modelled, not measured, and the authors list what the model cannot see. Every product on the shelf got an equal chance of being picked. The researchers had no market-share data. A shopper who always buys one fortified brand and a shopper who always buys an unfortified one count the same. The product survey dates from December 2020, formulations may have changed since, and the analysis does not address how well the body absorbs iodine from fortified drinks. Tom Sanders, professor emeritus of nutrition and dietetics at King’s College London, commenting on the study, warned that dietary intake records cannot reliably predict deficiency, because the iodine in plant foods depends on the soil they grew in. The paper also discloses that its lead author has received lecture honoraria from Oatly UK, Dairy UK and Dairy Council Northern Ireland, while its funder, the Biotechnology and Biological Sciences Research Council, had no role in the work.

Under the combined approach, average iodine intake for teenage girls at full dairy replacement reached 108 micrograms a day, above their starting average. The share of them below the requirement at that point was 43 percent, and for women aged 19 to 49 it was 21 to 22 percent at half replacement.