Can a plant based diet lead to iodine deficiency?

Nutritionist Rob Hobson explains why iodine is needed in the body, if plant based diets lead to iodine deficiency and, if so, how to avoid it.

According to the National Diet and Nutrition Survey (NDNS), intake of iodine appears to be particularly low among certain groups, especially teenage girls. One of the main sources of iodine in the diet is milk, so could ditching dairy in favour of a plant-based alternative put you at greater risk of deficiency, or can you get enough from other foods?

Why do we need iodine in the diet?

Iodine is used in the body to make thyroid hormones, which include the master hormone called thyroxine. These hormones help to control growth, repair cells and support a healthy metabolism. A very low intake of iodine means your thyroid has to work extra hard to maintain thyroxine levels in the blood, and in rare cases can cause swelling in the neck known as goitre (although this is very rare in the UK).

How much iodine do you need?

The UK recommended daily intake for iodine is 150mcg for adults and 200mcg for pregnant and breastfeeding women. The higher levels are required to ensure enough thyroid hormones are produced to help support the development of the baby's brain, and is a reason why low levels in teens are such as concern given the high rate of teenage pregnancies in the UK. Research has shown that many women in the UK have a lower level of iodine than is optimal for their child's development.

How much iodine do we get in the UK?

According to the NDNS, average adult (aged 19-64) intakes are above the Reference Nutrient Intake (RNI), showing that, on average, the UK population is getting enough of this nutrient. However, 15% of women and 9% of men do not get enough from their diet. Among teenagers the average intake is only 88% of the RNI, and 27% of girls and 14% of boys do not get enough iodine from their food.¹

Where do you find iodine?

Milk is the main source in the diet, but there are others, and it's important to take note of these if you are choosing to eliminate milk from your diet.

Why is milk one of the richest sources?

Milk and dairy products provide around 40% of the UK's overall intake of iodine. The reason milk is high in iodine is because it is added to cattle feed and the sanitising agents used to clean milking equipment.

Current food trends have had a big impact on milk consumption in the UK. The popularity of dietary regimes that promote the exclusion of dairy foods has seen a dramatic decrease in the number of milk drinkers, and as such there has been a large reduction in the value of milk sales over the years.

Why could going dairy free leave you at risk of deficiency?

A study carried out by the University of Surrey has warned that the trend to cut out dairy foods and switch to fashionable, non-dairy alternatives may be increasing the risk of iodine deficiency, especially among women. Researchers examined the iodine content of 47 milk alternative drinks (including soya, almond, coconut, oat, rice, hazelnut and hemp) and compared it with that of cow's milk.²

It was discovered that the majority of milk-alternative drinks did not have adequate levels of iodine, with concentration levels found to be around 2 per cent of that found in cow's milk. The findings from this study showed that most milk-alternative drinks are not an adequate substitute, as they all lack adequate iodine (a glass of a milk alternative drink would only provide around 2mcg iodine, compared to 100mcg in a glass of cow's milk).

How can you ensure your iodine intake in the absence of milk?

1. Take a daily multivitamin and mineral supplement that contains iodine.
2. Include at least one serving of white fish such as cod and haddock each week. These foods are one of the richest sources of iodine.
3. Explore the use of sea vegetables in your diet. Sushi is great and you can add seaweed to miso soup and salads. You can also buy dried seaweed thins in the snack aisles of supermarkets and health food shops.
4. Try swapping your cereal for eggs at breakfast. Two eggs provide around one-third of your recommended intake.

There is no reason to cut dairy foods (including milk) from your diet if you don't need to. Eating three servings of dairy foods each day can provide you with enough iodine to meet your daily requirement, alongside other foods in your diet.

If you need to go dairy free or choose to do so, then be mindful of your iodine intake and consider including other iodine-rich foods in your diet, or taking a supplement.