This piece was written by on of our contributors; registered nutritionist – Ghazal Abrishamchi.
An increasing number of people are now consuming milk-alternatives as a substitute for dairy products. While most people are aware of the issues this may raise around their calcium intake, many are unaware of the consequence in terms of their iodine intake.
Iodine is a mineral that is required for synthesis of thyroid hormones. Thyroid hormones play an important role in regulating our metabolism, as well as being essential for fetal brain development, normal growth, physical and mental development. Iodine requirement for adults is 150 mcg/d, and increases to 200 mcg/d in pregnant and breastfeeding women (1) .
In the UK, severe iodine deficiency is rare, however, mild-moderate iodine deficiency is relatively common. A large observational study looked at iodine status of pregnant women, and then 8-9 years later, assessed their child’s IQ and reading ability. They found that children of mothers with mild-moderate iodine deficiency, had lower IQs and worst reading ability compared to children of mother’s with optimal iodine status (2). This illustrates the importance of optimal iodine status during pregnancy. Inadequate or excess iodine intake can be problematic in all life-stages, leading to hypo/hyperthyroidism.
Sources of iodine:
In many countries, salt is now fortified with iodine. In the UK, however, no iodine fortification program has been introduced (although you can find iodised salt in some supermarkets) (3). This is because it is believed that salt iodisation policy would contradict the government advice to reduce salt intake, with 1 g of iodised salt providing between 20-30 mcg of iodine. Contrary to popular belief, Himalayan salt and sea salt are also not good sources of iodine.
Richest sources of iodine are seaweed, white fish and shellfish. However the most important source of any nutrient is one that is consumed most frequently and in large quantities. As such, the main sources of iodine in the UK diet are milk and milk products which contribute to 33% of adults iodine intake (4). It follows that anyone who does not consume milk and dairy products may have suboptimal iodine intake, with those excluding fish, meat, and eggs being particularly at risk of deficiency.
So then what options are available:
- Consuming alternative milks that have been fortified with iodine. Some brands that have fortified some of their products are: Oatly, Alpro, Koko and Marks & Spencer. However, even within these brands, not all products are fortified with iodine (currently). Therefore, always check the label. Also, some concerns have been raised around soy product consumption and thyroid function. However, a recent meta-analysis suggests that in healthy adults, soy products have no adverse effect on thyroid hormones (5).
- Supplementation – This should be as potassium iodide or potassium iodate (no more than 150 mcg/d), and not as kelp or seaweed supplement. If you are taking a multivitamin supplement, check the label to see if it contains any iodine, to avoid excessive intake.
- Fruit and vegetables also contain iodine, but the iodine content is variable and depends on the soil where they were grown on.
What about seaweed?
Iodine content of seaweed is highly variable, therefore, it is best that we don’t rely on seaweed as a source of iodine. Caution should especially be taken with brown seaweed such as kelp/kombu as iodine content of this type of seaweed is very high and can lead to excessive intake. Therefore, it is recommended that consumption of seaweed (mainly brown seaweed) is limited to 1 serve a week, especially in pregnant women (1) . Nori (e.g. in sushi) and other red and green types of seaweed have lower iodine content, and are generally considered to be safe.
Bear in mind that excessive iodine intake can be harmful. It may be worth speaking to a doctor or a dietitian if you are concerned about your iodine intake. Those with thyroids disease, and those with chronic low iodine intake, must speak to their doctor before supplementing their diet with iodine.
References
[1] Bath S, British D, Association D. Iodine Food Fact Sheet. Food Fact Sheet [Internet]. 2019 [cited 2020 May 11]; Available from: https://www.bda.uk.com/resource/iodine.html
[2] Bath SC, Steer CD, Golding J, Emmett P, Rayman MP. Effect of inadequate iodine status in UK pregnant women on cognitive outcomes in their children: Results from the Avon Longitudinal Study of Parents and Children (ALSPAC). Lancet [Internet]. 2013;382(9889):331–7. Available from: http://dx.doi.org/10.1016/S0140-6736(13)60436-5
[3] Bath SC, Button S, Rayman MP. Availability of iodised table salt in the UK – Is it likely to influence population iodine intake? Public Health Nutr. 2014;17(2):450–4.
[4] The Scientific Advisory Committee. Sacn Statement on Iodine and Health.
2014;(February):1–44.
[5] Otun J, Sahebkar A, Östlundh L, Atkin SL, Sathyapalan T. Systematic Review and Meta-
analysis on the Effect of Soy on Thyroid Function. Sci Rep. 2019;9(1):1–9.
[6] Advice on brown seaweed for pregnant women; breastfeeding women and children (27 June 2011) [Internet]. [cited 2020 May 11]. Available from:
https://www.foodstandards.gov.au/consumer/safety/brownseaweed/Pages/default.aspx
