Iodine status: cows’ milk versus plant-based drinks

Data from the UK National Diet and Nutrition Survey

Iodine is a mineral that is present in a limited number of foods, such as fish, eggs and milk and dairy products. Iodine contributes to the normal production of thyroid hormones. It also contributes to the normal functioning of the nervous system. There is emerging evidence that mild-to-moderate iodine deficiency during pregnancy is associated with suboptimal child neurodevelopment outcomes. The role of pre-pregnancy iodine stores seems to be important to ensure adequate supplies of iodine during pregnancy.

Iodine in milk and dairy products

Iodine status: cows’ milk versus plant-based drinksAs there is no formal universal salt-iodisation policy in the United Kingdom (UK), dietary sources are more important determinants of iodine intake. In the UK, milk and dairy products are an important source of iodine. Data from the UK National Diet and Nutrition Survey (NDNS) 2014-2016 show that milk and dairy products contributed to 51% of the average daily iodine intake of children (4-10 years), to 40% of the iodine intake of adolescents (11-18 years) and to 35% of the iodine intake of adults (19-64 years). A study that measured iodine content in milk samples from different UK supermarkets, found that a glass of milk (200 ml) contains on average 85 µg iodine. This is equal to 57% of the World Health Organization (WHO) recommended daily intake for adults and 34% of the WHO recommended daily intake for lactating and pregnant women.

Plant-based drinks

Recently, plant-based drinks, such as soy, almond and rice drinks, are becoming more popular. In 2019, 23% of UK adults used plant-based drinks, compared to 19% in 2018 and 14% in 2017. The consumption is higher among women and in those below the age of 35 years. Plant-based drinks, unless fortified, contain less iodine than cows’ milk (median 7 vs 438 μg/kg, respectively). Data from 2015 shows that most plant-based drinks in the UK were not fortified with iodine. Since then, some brands have started adding iodine to their plant-based drinks, however, most are still not fortified. This is of concern, as consumers of these drinks may be at risk of iodine deficiency. Moreover, young women, for whom an adequate iodine status seems to be extra important, are more likely to consume plant-based drinks.

Measuring iodine intake and status

Following these concerns, a recent study investigated the iodine status and iodine intake from food of consumers of cows’ milk and consumers of unfortified plant-based drinks (e.g., almond, soya, oat, rice, coconut and hemp drinks). To do so, data from the NDNS from years 7-9 (2014-2017; before a few manufacturers fortified their plant-based drinks with iodine) was used. In the NDNS, iodine status was measured using iodine concentration in spot-urine (UIC, μg/L) and dietary iodine intake was assessed using four-day food diaries.

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Results

The current study included almost 4000 individuals. Plant-based drinks were consumed by 4.6% of individuals of whom 2.2% consumed those drinks exclusively. Exclusive plant-based drinks consumers had a lower iodine intake than those who consumed only cows’ milk (about 94 vs about 129 μg/day). Those only consuming plant-based drinks were also indicated as iodine deficient, whereas cows’ milk consumers were iodine-sufficient. The average iodine intake of women of childbearing age who were exclusive consumers of plant-based drinks was 86 µg/d, which is below the UK Reference Nutrient Intake of 140 μg/day. The urinary iodine concentration of women of childbearing age (107 µg/l) was found well below the WHO criterion for sufficient iodine intake in pregnancy (≥ 150 µg/l). Moreover, when comparing women of childbearing age who consumed plant-based drinks exclusively and those who exclusively consumed cows’ milk, only those who consumed cows’ milk were iodine sufficient by the WHO criteria. This is of concern because it is important to have sufficient iodine intake prior to pregnancy to ensure optimal thyroidal iodine stores that can be drawn upon to support the higher demand for iodine during gestation

Iodine: Food Fact Sheet

For more information and advice, please refer to the BDA fact sheet on iodine.

Key points

  • Milk and dairy products are an important source of iodine in the UK diet: they contribute to 35% of iodine intake of adults
  • Plant-based drinks are becoming more popular but, unless fortified, contain less iodine compared to cows’ milk
  • A new study investigated the iodine intake and status of consumers of cows’ milk and consumers of unfortified plant-based drinks. Exclusive consumers of plant-based drinks had a lower iodine intake than consumers of cows’ milk. The first group was also indicated as iodine deficient, whereas cows’ milk consumers were iodine-sufficient
  • These results indicate that consumers who take unfortified plant-based drinks exclusively, might be at risk of iodine deficiency. Especially if they do not consume iodine containing supplements or other animal foods high in iodine, such as fish and eggs