The need for adequate iodine intake

Iodine is an essential trace element that needs to be obtained through the diet and is essential for human life. The primary role of iodine is as a component of the hormones thyroxine (T4) and triiodothyronine (T3) produced by the thyroid gland^{(Reference Zimmermann, Jooste and Pandav6)}. T4 is converted to the metabolically active form T3^{(Reference Luongo, Dentice and Salvatore7)} in the peripheral tissues, which binds to nuclear thyroid hormone receptors and regulates the expression of a wide range of genes.

Iodine deficiency, through impaired thyroid hormone synthesis, can lead to a range of adverse effects collectively termed ‘iodine deficiency disorders’^{(Reference Zimmermann, Jooste and Pandav6)}. Iodine deficiency disorders can affect all stages of life with a variety of symptoms, including hypothyroidism, stillbirth, impaired mental function, congenital anomalies and iodine-induced hyperthyroidism^{(Reference Li and Eastman8)}. The effects of iodine deficiency relate to the role of thyroid hormones (through the activation of thyroid-specific genes) on essential physiological processes, such as metabolism, the development and maturation of the central nervous system, the musculoskeletal system and the lungs^{(Reference Bernal, Feingold, Anawalt, Boyce, Chrousos, de Herder, Dungan, Grossman, Hershman, Hofland, Kaltsas, Koch, Kopp, Korbonits, McLachlan, Morley, New, Purnell, Singer, Stratakis, Trence and Wilson9,Reference Bassett and Williams10)} . Additionally, T3 regulates brain development by regulating neuronal proliferation and migration, glial differentiation and myelination of axons in the central nervous system^{(Reference Bernal, Feingold, Anawalt, Boyce, Chrousos, de Herder, Dungan, Grossman, Hershman, Hofland, Kaltsas, Koch, Kopp, Korbonits, McLachlan, Morley, New, Purnell, Singer, Stratakis, Trence and Wilson9)}. This makes iodine essential for brain and neurological development during pregnancy and infancy^{(Reference Ausó, Lavado-Autric and Cuevas11)}, and indeed, the World Health Organization (WHO) considers iodine deficiency the most preventable cause of infant brain damage⁽¹²⁾. The most visible effect of iodine deficiency is goitre (enlargement of the thyroid gland), but the most serious is cognitive impairment. Population iodine status is primarily assessed by comparing the median urinary iodine concentration (UIC) against WHO thresholds (< 20 µg/l = severe deficiency, 50–99 µg/l = mild deficiency, 20–49 µg/l = moderate deficiency, ≥ 100 µg/l = sufficiency in the population). During pregnancy and lactation, the physiological requirement for iodine is increased to meet the demands of foetal development, and therefore, the median UIC to define sufficiency in the pregnant population is higher (at 150–249 µg/l).

Impairment of foetal neurological development is irreversible and has lifelong consequences. Insufficient intake of iodine during pregnancy can adversely affect maternal thyroid health and the infant’s neurological development^{(12,Reference Leung, Pearce and Braverman13)} . In its most extreme form, deficiency can lead to congenital iodine deficiency disorder (characterised by growth retardation and intellectual impairments), pregnancy loss as well as an increased risk of infant mortality⁽¹²⁾. Iodine insufficiency, even marginal, has been shown to affect children’s cognition and school performance in the UK^{(Reference Bath, Steer and Golding14)}. Results from the Avon Longitudinal Study of Parents and Children in the UK show that children of mothers with mild-to-moderate iodine deficiency in the first trimester were more likely to have verbal IQ and reading scores in the lowest quartile at eight and nine years of age respectively, than children from mothers in the iodine-sufficient group^{(Reference Bath, Steer and Golding14)}. Other observational studies have shown that children born to mothers with mild-to-moderate iodine deficiency can have increased neurological and psychological problems, hyperactivity, and decreased spelling and language scores^{(Reference Leung, Pearce and Braverman13,Reference Bath15)} .

Iodine intake recommendations

The WHO recommend a daily intake of 90 μg for children aged 0–59 months, 120 μg/d for children aged 6–12 years, and 150 μg/d for adolescents and adults, increasing to 250 μg/d for pregnant and lactating women⁽¹²⁾. In the UK, iodine intake recommendations differ marginally from those made by the WHO, the reference nutrient intake (RNI) for adults is 140 μg/d, and the lower reference nutrient intake (LRNI) is 70 μg/d (considered to be the minimum necessary intake to avoid the development of goitre in a population)⁽¹⁶⁾. Unlike the WHO, the UK does not recommend an increased iodine intake during pregnancy. Instead, it is advised that women of reproductive age maintain a habitual iodine intake sufficient to support the increased demands of pregnancy without requiring additional supplementation⁽¹⁶⁾. This approach assumes that iodine stored in the thyroid, capable of maintaining thyroid hormone production during the early stages of pregnancy, is adequate to meet maternal and foetal needs^{(Reference Zimmermann17)}. However, for many women, iodine stores might be limited if a long period of insufficient iodine intake has occurred^{(Reference Zimmermann17)}. As a result, in countries with no or limited access to iodised salt, such as the UK, the WHO recommends that all women of reproductive age should supplement with iodine to ensure that total iodine intake is adequate^{(12,Reference Andersson, de Benoist and Delange18)} .

Iodine status in the UK

Concern that iodine status in the UK is suboptimal was heightened in 2011 when the country’s first national survey of iodine status for over sixty years revealed mild iodine deficiency in UK schoolgirls^{(Reference Vanderpump, Lazarus and Smyth19)}. Urinary iodine concentration (UIC), a measure of population iodine status⁽²⁰⁾, was measured in 737 adolescent schoolgirls (14–15 years) across nine regions in the UK. The median UIC (80 µg/l, IQR 57–109) indicated mild iodine deficiency in the cohort (the WHO threshold for sufficiency is 100 µg/l⁽¹²⁾), highlighting the potential risk to future generations and the need for iodine prophylaxis. By contrast, a multi-centre pilot study in 2012/13 found that iodine status in UK children aged 8–10 years was sufficient with a median UIC of 144 µg/l (IQR 95–223 µg/l)^{(Reference Bath, Combet and Scully21)}. However, there is evidence that dairy consumption, especially that of milk, declines with age, which suggests that children may not be a representative group and could potentially present a biased estimation of population iodine status in populations where milk is a major source of iodine, such as in the UK^{(Reference Dror and Allen22)}.

Iodine intake and status in the UK are assessed as part of the National Diet and Nutrition Survey (NDNS) rolling programme. According to NDNS data, the median iodine intake (assessed by food diaries) has been above the UK RNI for adults since Year 1 of the Rolling Programme (in 2008/09). However, in the most recent report (for 2018/19) the median intake for adults, at 138 μg/d was below the UK RNI (and the WHO recommendation), with 10 % of individuals having an intake below the LRNI^(23–26). For adult women only, the latest median intake figure was lower at 124 μg/d, with 12 % below the LRNI^(23–26). Iodine intake in girls aged 11–18 years has been below the UK and WHO recommendations since Year 1, with the most recent result of a median of 88 μg/d being 65 % of the UK RNI, and 28 % having an iodine intake below the LRNI^(23–26). These girls may become pregnant in the short-to-medium term, so low iodine intake is concerning as stores of iodine would not be optimised prior to pregnancy and may, therefore, affect offspring neurodevelopment.

In 2013, the NDNS also began collecting spot-urine samples from participants for UIC analysis. Results from Years 9–11 of the NDNS programme indicate that the median UIC of women of childbearing age (16–49 years) at 98 μg/l⁽²³⁾ (20th percentile, 47 μg/l; 80th percentile, 176 μg/l) was below the WHO adequacy threshold (of 100 μg/l⁽¹²⁾). The WHO also suggests that no more than 20 % of UIC values should be below 50 μg/l for a population to be classified as iodine sufficient⁽¹²⁾. In women of childbearing age in NDNS, the proportion of UIC values below 50 μg/l increased from 11 % to 21 % between Year 6 (the first year with UIC data) and Years 9–11^(23,24) , suggesting that this group of the UK population have inadequate iodine status.

In addition to women of childbearing age, other population groups are at risk of iodine insufficiency in the UK, especially if their iodine demands are increased (e.g. during pregnancy) or if they routinely exclude iodine-rich foods (e.g. dairy products and seafood) from their diets. A systematic review^{(Reference Eveleigh, Coneyworth and Avery27)} found that those following a strict plant-based diet (i.e. vegans) and were not consuming iodine supplements or seaweed (a plant-based source of iodine) had an increased risk of iodine insufficiency, low iodine status, and inadequate iodine intake in comparison to adults following less restrictive plant-based diets (e.g. vegetarians). According to data collected between 2018 and 2019, the UK demographic most commonly adhering to a plant-based diet were females aged 18–34 years^{(Reference Wunsch28)}. Women in this age group are particularly vulnerable to the effects of iodine insufficiency, particularly during pregnancy and lactation, as iodine intake requirements increase to support the needs of the growing foetus⁽¹²⁾. Addressing the potential implications for iodine intake and public health becomes essential as the trend towards plant-based eating grows.

Dietary choice and iodine intake

Iodine status in many population groups in the UK depends on individual food choices. This is because, unlike many other countries, there is currently no legislation on salt iodisation in the UK^{(Reference Bath, Verkaik-Kloosterman and Sabatier29)}, and iodised salt is not widely available^{(Reference Bath, Button and Rayman30)}; achieving adequate iodine intake is more challenging and relies on dietary iodine sources alone. The primary dietary sources of iodine in the UK, in terms of iodine content, are seafood, eggs, milk and dairy products⁽³¹⁾. The main food sources of iodine can vary between countries and regions within the same country^{(Reference Preedy, Burrow and Watson32)}, driven by differences in food choices, fortification policies, and the high variability of iodine content in foods. This variability arises from factors such as the iodine content of the soil, agricultural practices, and seasonal changes^{(Reference Preedy, Burrow and Watson32,Reference Haldimann, Alt and Blanc33)} . Fortification policies – or the lack thereof – play a crucial role in shaping iodine intake patterns. In countries with mandatory salt iodisation, such as Romania⁽³⁴⁾, iodised salt significantly contributes to dietary iodine intake, reducing reliance on other food sources. By contrast, the absence of mandatory salt iodisation in the UK makes iodine intake highly dependent on naturally iodine-rich or iodine-fortified foods⁽³⁴⁾. This reliance means that cow’s milk and dairy products play a disproportionately large role in iodine intake in the UK^{(Reference Bath, Verkaik-Kloosterman and Sabatier29,34)} .

Regular consumption of iodine-rich foods is required to meet the recommended iodine intake for adults in the UK. For instance, the recommended 140 μg/d could be met through the weekly consumption of one portion of white fish (∼150 μg/portion), one portion of oily fish or seafood (∼57–74 μg/portion), alongside daily consumption of three portions of dairy (e.g. one glass of milk (∼60 μg/portion), one yoghurt (∼55 μg/portion) and one serving of cheese (∼15–35 μg/portion))^{(Reference Finglas, Roe and Pinchen35)}. However, the growing popularity of plant-based diets poses a challenge to this dietary pattern. As more consumers reduce or eliminate their intake of fish and dairy products, they risk inadequate iodine intake unless they receive appropriate guidance on replacing these iodine-rich foods with fortified alternatives or supplements.

Milk as a source of iodine

Milk and dairy products are the primary sources of iodine in many countries, contributing ∼12–53 % of total daily iodine intake^{(Reference Bath, Verkaik-Kloosterman and Sabatier29)}. Cow’s milk has a naturally low iodine concentration but is a rich source of iodine because iodine concentration is increased through standard farming practices, such as adding iodine salts to cattle feed and using iodine-based disinfectants known as iodophors during the milking process^{(Reference Bath and Rayman36,Reference van der Reijden, Zimmermann and Galetti37)} . Countries such as Australia and New Zealand have replaced iodophors with other disinfectants, which may explain the decline in milk iodine concentration in those countries^{(Reference Thomson38)}. Similarly, the considerable variability in milk iodine content within and between countries is likely a result of differences in farming practices^{(Reference van der Reijden, Zimmermann and Galetti37)}.

UK cow’s milk is a good source of iodine (at 427 μg/l^{(Reference Stevenson, Drake and Givens39)}) and has a higher concentration than in many other countries^{(Reference van der Reijden, Zimmermann and Galetti37,Reference Tattersall, Peiris and Arai40)} . In the UK, a 200 ml glass of cow’s milk provides 85 μg of iodine, constituting ∼57 and 34 % of the recommended iodine intake for adults (150 μg/d) and pregnant women (250 μg/d), respectively⁽¹²⁾. In addition, seasonal variation in milk-iodine concentration exists, whereby winter milk has a higher iodine concentration than summer milk^{(Reference van der Reijden, Zimmermann and Galetti37,Reference Tattersall, Peiris and Arai40)} . This results from a greater reliance on mineral-fortified feed during winter when cattle are housed indoors rather than grazing on pasture^{(Reference van der Reijden, Zimmermann and Galetti37)}. Studies in the UK and other European countries have shown that organic milk is lower in iodine content than conventional milk^{(Reference Tattersall, Peiris and Arai40)} due to restrictions on mineral-fortified feed and a higher proportion of goitrogenic components in feed. Despite this, organic cow’s milk is still a good source of iodine, and more recent research suggests no overall difference in iodine concentration between organic and conventional milk in the UK, likely due to changing farming practices in the organic sector^{(Reference Qin, Faludi and Beauclercq41)}.

Milk and dairy products have consistently contributed the most iodine to daily intake in the UK since the inception of the NDNS, for example contributing over 30 % of adult intake and over 50 % of iodine intake for children 4–10 years⁽²³⁾. However, consumer trends indicate that UK consumers buy less liquid milk and more of other dairy products, such as cheese and yoghurt^(42,43) . These trends are expected to continue into 2030 and beyond⁽⁴³⁾. Whilst there is no single explanation for the decline, hypotheses include changes to the food environment (e.g. increased choice of drinks), generational differences in food choice and perceptions of foods, changes in the household use of milk (i.e. from a standalone drink to a component of hot beverages), and the expansion of the plant-based milk alternative sector^{(Reference Stewart, Dong and Carlson44)}.

Plant-based milk alternatives as a source of iodine

Plant-based milk alternative products, made from extracts of plant materials (such as soya, grains, and nuts), are commonly consumed as substitutes for cow’s milk products. According to research from Mintel, one in three (34 %) UK adults were using plant-based milk alternatives in 2023–2024 up from 19 % in 2017–2018⁽⁴⁵⁾. It appears that young adults are driving this trend, with 46 % of 16–34-year-olds and 44 % of parents of children under 18 years old reporting consuming plant-based milk alternatives. Perceived healthfulness and environmental concerns are two common reasons for choosing plant-based dairy alternatives^{(Reference Vainio, Niva and Jallinoja46–48)}.

However, the plant materials used to create plant-based milk alternatives are low in iodine, and there is currently no guidance or legislation on the fortification of these products. As a result, not all plant-based milk alternatives are fortified to an iodine concentration equivalent to cow’s milk. Studies from the UK^{(Reference Bath, Hill and Infante49)}, Norway^{(Reference Dahl, Aarsland and Næss50)}, and the USA^{(Reference Ma, He and Braverman51)} have shown that, unless fortified with iodine, plant-based milk alternatives have a low iodine concentration – just 2 % of the value of UK cow’s milk (year-round value of 344 µg/kg)^{(Reference Bath, Hill and Infante49)}. Consequently, a 200 g portion of unfortified plant-based milk alternatives would provide 0·9–4·3 µg of iodine^{(Reference Bath, Hill and Infante49)} (v. 60 µg/portion for UK cow’s milk). In 2015, only 6 % of plant-based milk alternatives available in UK supermarkets were fortified with iodine^{(Reference Bath, Hill and Infante49)}. By 2020, a market survey showed that the proportion of plant-based milk alternatives fortified with iodine had increased to 20 %^{(Reference Nicol, Thomas and Nugent5)}. Despite this increase, the likelihood of consumers selecting an iodine-fortified product remains low as the majority of the products on the market remain unfortified with iodine. The 2020 market survey also showed that when plant-based milk alternatives were fortified with iodine, their iodine concentration was 43–150 % of conventional cow’s milk (60 µg/portion)^{(Reference Nicol, Thomas and Nugent5)}; the majority of iodine-fortified products were at a concentration of 22·5 µg/100 ml (i.e. to be labelled as a source of iodine), which could be considered a reasonable substitute for cow’s milk in terms of iodine content.

Impact of switching to plant-based milk alternatives

Several studies have investigated the iodine intake and status of vegans and vegetarians in the UK^{(Reference Whitbread, Murphy and Clifton52–Reference Kristensen, Madsen and Hansen54)} and other countries^{(Reference Whitbread, Murphy and Clifton52–Reference Kristensen, Madsen and Hansen54)}, tending to show that vegans are at particular risk of iodine deficiency. Studying these groups provides insight into how plant-based diets influence iodine intake and status. However, it does not necessarily reflect the impact of substituting cow’s milk with plant-based alternatives at a population level. For example, vegetarian diets may include some plant-based milk alternatives but may also include cow’s milk and dairy products, while vegan diets exclude all milk and dairy products and are more likely to include plant-based substitutions, but vegans do not consume iodine-rich foods such as fish. A study using iodine intake and status data from the NDNS (years 7–9; 2014–2017) observed that those consuming plant-based milk alternatives had a lower iodine intake (94 v. 129 µg/d) and status (median UIC: 79 v. 132 µg/l) compared to cow’s milk consumers^{(Reference Dineva, Rayman and Bath55)}, suggesting that plant-based milk alternative consumers were not seeking out an alternative source of iodine elsewhere in the diet. These results are meaningful, as the cow’s milk consumers were classified as iodine-sufficient (132 µg/l) according to the WHO cut-off (median UIC: 100 µg/l), whereas those exclusively consuming plant-based milk alternatives were classified as iodine-deficient (79 µg/l). However, this study used data from NDNS during a time when very few manufacturers fortified their drinks with iodine (i.e. approximately 6 % of the market in 2014–2017)^{(Reference Bath, Hill and Infante49)}. Therefore, there is little information regarding the impact of iodine-fortified plant-based milk alternatives on dietary iodine intake.

Dietary modelling is one of several research tools available to assist with the population-wide transition to more environmentally sustainable diets while maintaining nutritional adequacy. It is particularly useful for predicting future nutritional changes relatively quickly and inexpensively. Once identified, there is the potential to avert adverse changes, for example, by tailoring policies and public health messages. Several dietary modelling studies have assessed the impact of replacing milk with plant-based milk alternatives^{(Reference Temme, van der Voet and Thissen56–Reference Demmer, Cifelli and Houchins61)}, but very few have specifically investigated the impact on iodine intake.

In the UK, a modelling study^{(Reference Nicol, Nugent and Woodside62)} using data from years 9–11 of the NDNS report identified that entirely replacing cow’s milk consumption with an unfortified or organic (which cannot be fortified) plant-based milk alternative would increase the risk of iodine insufficiency across both children and females aged 11–18 and 19–49 years. However, a plant-based milk alternative fortified to either 22·5 µg/100 g or 27·4 µg/100 g would seem to be an adequate replacement for cow’s milk in terms of iodine intake, suggesting that the optimal concentration for iodine fortification is approximately 27·4 µg/100 g^{(Reference Nicol, Nugent and Woodside62)}. When iodine intake was modelled, taking into consideration the probability of consumers selecting an iodine-fortified product based on the current market offering, an 18–44 % decrease in iodine intake was observed across all age groups. Similar results were found in France, using data from the French Third Individual and National Study on Food Consumption Survey; Salomé et al.^{(Reference Salomé, Huneau and Le Baron63)} reported that replacing milk with unfortified plant-based milk alternatives would decrease the probability of achieving an adequate iodine intake^{(Reference Salomé, Huneau and Le Baron63)}. However, this study did not include any iodine-fortified products in their modelling.

The nutritional implications of switching from cow’s milk to plant-based milk alternatives are unlikely to be the same for all population groups. For example, milk accounts for over half of the iodine intake in young children⁽²³⁾, and the high cow’s milk intake in children is one possible explanation for the iodine sufficiency observed in UK children⁽²³⁾. Consequently, transitioning from cow’s milk to plant-based alternatives could greatly affect iodine intake, depending on the level of fortification. For example, when modelling the impact of different concentrations of iodine fortification in readily available plant-based milk alternatives, replacing usual cow’s milk consumption with unfortified plant-based milk alternatives would reduce iodine intake and increase the proportion of UK children with intakes below the LRNI^{(Reference Nicol, Nugent and Woodside62)}. Plant-based milk alternatives fortified with iodine at the highest concentration available in UK supermarkets (45 µg/100 ml) may not be suitable for regular consumption in young children as the proportion of those with iodine intakes above the tolerable upper limit (UL) increased by 23 %^{(Reference Nicol, Nugent and Woodside62)}. However, it should be noted that the UL for children is not based specifically on evidence of direct harm to children but is extrapolated from the adult UL meaning that the risk of excess iodine intake in this age group is not well known, although excess iodine intake can increase the risk of developing iodine-induced thyroid dysfunction^{(Reference Leung and Braverman64)}. A plant-based milk alternative fortified at a high iodine concentration would mean year-round exposure to this high concentration, whereas the effects of the high concentration in winter cow’s milk may be offset by the lower values in the summer months.

Adolescent girls (11–18 years) and women of reproductive age (19–49 years) are known to have a lower iodine intake and status compared to the general population⁽²³⁾, and pregnant women in the UK are classified as iodine-deficient⁽³⁴⁾. Some of the reasons for these population groups having a lower iodine intake are avoidance of iodine-rich foods such as seafood and dairy products^(23,65) , and this group is more likely to adopt a plant-based diet⁽⁶⁶⁾ and use plant-based milk alternatives⁽⁴⁸⁾. Therefore, replacing cow’s milk with a plant-based alternative could further reduce iodine intake in this population group. For example, we found that replacing usual cow’s milk consumption with an unfortified plant-based milk alternative would reduce iodine intake and would increase the proportion of adolescent girls and women of reproductive age with intake below the LRNI to 48 % and 33 %, respectively^{(Reference Nicol, Nugent and Woodside62)}. Maintaining sufficient iodine status as an adult is necessary at all stages of life but is especially for women of reproductive age who may go on to become pregnant.

Although these studies indicate that consumers of plant-based milk alternatives might be at risk of iodine deficiency, it is important to note that the influence of the consumption of plant-based milk alternatives on iodine intake and status will depend on the composition of the overall diet (i.e. intake of other iodine-rich food sources, such as seafood); data shows that in 2024, 78 % of plant-based milk alternative consumers also consume cow’s milk⁽⁴⁸⁾ and therefore the impact will depend on whether there is partial or total replacement of cow’s milk and the quantities consumed overall.

Plant-based milk alternatives in food-based dietary guidelines

Milk and dairy products are listed as a core food group in approximately three-quarters (75 %) of food-based dietary guidelines globally^{(Reference Herforth, Arimond and Álvarez-Sánchez67)}, and almost half of guidelines also include plant-based alternatives^{(Reference Comerford, Miller and Boileau68)}. Many food-based dietary guidelines increasingly recommend reducing dairy food consumption, including milk, to meet health and environmental goals, however, the impact this could have on iodine intake is often overlooked. For instance, the British Dietetic Association’s (BDA) One Blue Dot policy⁽⁶⁹⁾ and the UK Eatwell Guide⁽⁷⁰⁾ consider milk and dairy products to be a core food and suggest that plant-based milk alternatives can be consumed interchangeably with dairy products. While these recommendations encourage choosing a calcium-fortified product, they do not clearly stipulate that consumers should ensure that these products are fortified with iodine. This framing may lead consumers to believe that plant-based milk alternatives are nutritionally equivalent to cow’s milk. Unless iodine fortification of plant-based milk and dairy alternatives becomes more prevalent, individuals consuming these products as a replacement for dairy products (e.g. vegans) may be at risk of iodine insufficiency.

The EAT-Lancet Commission’s reference diet also overlooked iodine as it was not considered an essential micronutrient in its model^{(Reference Willett, Rockström and Loken1)}; the dietary recommendations for dairy foods are mainly rooted in calcium intake needs. This approach underestimates milk and dairy products’ role in meeting iodine requirements, particularly in countries like the UK, where cow’s milk and dairy products are the primary dietary iodine sources.

In a recent review, we evaluated the iodine content provided by the EAT-Lancet reference diet, and findings underscored the importance of dairy as a significant iodine source within this framework^{(Reference Nicol, Nugent and Woodside71)}. The EAT-Lancet reference diet suggests the optimal consumption of dairy foods is 250 g per day, with a range of 0–500 g per day^{(Reference Willett, Rockström and Loken1)}. This equates to 1·25 portions of dairy foods per day (range: 0–2·5 portions), which falls below the BDA’s recommendation of 3 portions per day^{(Reference Jones72)}. The EAT-Lancet reference diet would provide 128 μg/d, or 85 % of the WHO’s recommended iodine intake for adults (150 μg/d). When considering the range of intake suggested for each food category, the iodine provision could be as low as 8 µg/d (6 % of adult RNI) or as high as 295 µg/d (196 % of daily adult RNI)^{(Reference Nicol, Nugent and Woodside71)}. However, the EAT-Lancet Commission recommends that the intake of animal-sourced foods, such as dairy foods, should be as close to zero as possible to meet planetary boundaries^{(Reference Willett, Rockström and Loken1)}. When dairy foods in the EAT-Lancet reference diet were replaced with unfortified plant-based alternatives, total iodine provision dropped substantially to 54 μg/d, only 34 % of the recommended intake for adults. It is important to note that the EAT-Lancet Commission specifies that it does not imply that the global population should eat the same foods or prescribe an exact diet^{(Reference Willett, Rockström and Loken1)}. Instead, local interpretation and adaptation are necessary and should reflect the culture, geography, and demography of the population and individuals^{(Reference Willett, Rockström and Loken1)}. This means there may be a gap between the EAT-Lancet recommendations and what is optimal for adequate nutrient intake and health in each country. However, the considerable reduction in iodine provision highlights the necessity for more comprehensive guidelines that encourage iodine fortification in plant-based milk alternatives to ensure adequate iodine intake in populations increasingly shifting away from cow’s milk.

The case for the fortification of plant-based milk alternatives with iodine

As previously discussed, fortifying plant-based milk alternatives with iodine offers a promising approach to avoid decreases in iodine intakes when shifting towards plant-based alternatives. Given that plant-based milk alternatives are often marketed as substitutes for cow’s milk, fortification with iodine could align with consumer expectations of nutritional equivalence. This equivalence is primarily limited to calcium in plant-based alternatives^{(Reference Nicol, Thomas and Nugent5)}, highlighting a gap in addressing other key micronutrients such as iodine.

For fortification to be effective, this practice must be carefully designed and standardised. Without standardisation, fortification initiatives may lack consistency, risking variability in iodine intake among consumers who may rely on these products as a plant-based source of iodine. Such measures would be instrumental in preventing population-level decreases in iodine intake as plant-based diets grow more popular. However, fortification scenarios must be closely monitored beforehand to ensure the goals are attained while not causing excessive intake.

Consumer perceptions regarding fortified plant-based milk alternatives also play a critical role in determining the success of fortification efforts. Consumer acceptance of fortified products is related to the perceived health benefits and nutritional value^{(Reference Jahn, Tsalis and Lähteenmäki73)}. Yet, low awareness of iodine’s role in health may present a challenge; consumer knowledge of iodine is often limited^{(Reference O’Kane, Pourshahidi and Farren74,Reference Combet, Bouga and Pan75)} despite its recognised importance for public health.

Additionally, while fortification can enhance the nutrient profile of plant-based milk alternatives, it may also detract from these products’ perceived naturalness. For some consumers, fortification implies a move away from ‘natural’ ingredients^{(Reference Baker, Lu and Parrella76)}, which may affect their purchasing choices. This sentiment is particularly strong among those who prioritise organic products, which, by UK regulations, cannot be fortified. Such preferences could limit the reach of fortification programmes, potentially leaving a segment of consumers without a reliable iodine source.

Another consideration is the bioavailability of minerals added to plant-based milk alternatives, which depends on the food matrix and the type of fortificants. For instance, in vitro and human isotope studies examining calcium bioavailability in fortified plant-based beverages made from rice, cashews, almonds, coconuts, oats, and soya have reported considerable variability^{(Reference Zhao, Martin and Weaver77–Reference Smith, Dave and Hill81)}. This emphasises the need for investigation into the bioavailability of iodine specifically, as it has not yet been studied in plant-based milk matrices. Previous research has also shown that shaking plant-based milk alternatives before use is necessary for the transfer of fortified nutrients in the aqueous solution, otherwise, it deposits at the bottom of the carton and are not consumed as intended; studies have shown decreased calcium levels of up to 97 % for unshaken compared to shaken samples^{(Reference Smith, Dave and Hill81)}. Understanding these factors in relation to iodine is essential to ensure that fortification efforts meet consumers’ nutritional needs.

Options for plant-based milk alternative consumers to optimise iodine intake

It is important to note that consumption of plant-based milk alternatives and iodine sufficiency do not have to be mutually exclusive. There are ways to optimise iodine intake for those choosing plant-based milk alternatives. For example, individuals should opt for iodine-fortified plant-based alternatives or increase their iodine intake from other food sources. However, if this is not possible, or if the quantity of iodine-fortified milk alternative intake is low, then a suitable iodine-containing supplement would be a more consistent and reliable way of ensuring adequate iodine intake. If a supplement is considered, this should not be a seaweed/kelp supplement due to the potential for excessive iodine intake but instead^{(Reference Zimmermann and Delange82)}, iodine should be in the form of potassium iodide or potassium iodate with a dose that does not exceed 150 µg/d.