Dr Justine Butler from Viva! examines the best ways to get iodine into your diet.
Government guidelines recommend that adults get 140 micrograms of iodine a day. A microgram is a millionth of a gram, so we need only a very small amount, but getting that small amount is vital.
The UK has been considered iodine-sufficient for many years, but there is now some concern that iodine deficiency may be more prevalent than previously thought. In pregnancy, this could affect brain development in infants. There is no current recommendation in the UK to take iodine supplements during pregnancy and the NHS reckons you should be able to obtain all the iodine you need by eating a varied diet.
Signs of iodine deficiency include an enlarged thyroid gland (goitre), tiredness, weight-gain, increased susceptibility to infections, depression, feeling cold at all times and dry and cracked skin.
On the other hand, too much iodine can disrupt thyroid function, leading to weight gain, hypothyroidism or hyperthyroidism. The Department of Health advise that intakes of up to 500 micrograms a day of iodine are unlikely to cause harm.
Are we getting enough?
According to the UK Scientific Advisory Committee on Nutrition (SACN), there is public health concern that many people may not be getting enough iodine, regardless of their diet, especially during adolescence, reproduction, gestation and development. The 2018 National Diet and Nutrition Survey found low levels of iodine in nine per cent of children aged 4-10 years, 12 per cent of children aged 11-18 years, 14 per cent of adults aged 19-64 and eight per cent of adults aged 65 years and over.
So where can we get it? It is a trace element found in seawater, rocks and some types of soil, so the iodine content of food depends on the amount of iodine in the soil or water from which it came. For some foods, such as cow’s milk, farming practices also affect iodine content.
The major animal food sources include dairy products and fish, but sea fish and shellfish are often contaminated with polychlorinated biphenyls (PCBs), dioxins and mercury. Raw and undercooked fish and shellfish can also contain harmful viruses and bacteria.
The iodine in cow’s milk is not a natural component, but comes from iodine supplements in cattle feed and iodine-containing disinfectants used to sterilise milking equipment and added to teat dips and udder washes! Iodine has been used in the treatment of wounds for more than 170 years and as dairy cows’ udders are prone to infection (mastitis) they are routinely washed with iodine and some of it ends up in their milk.
There is a wide seasonal variation in the iodine content of cow’s milk, with substantially higher levels found in winter when cows are confined indoors and fed only iodine-fortified feed. Organic dairy products contain over 40 per cent less iodine than non-organic.
Plant foods containing iodine include wholegrains, green beans, courgettes, kale, spring greens, watercress, strawberries and organic potatoes with skin. However, amounts tend to be low and variable depending on how much iodine is in the soil.
The 2016 European Prospective Investigation into Cancer and Nutrition (EPIC Oxford) study was made up of 18,244 meat-eaters, 4,531 fish-eaters, 6,673 vegetarians and 803 vegans. It suggested that vegans were falling short of iodine, but the food frequency questionnaire used in this study did not record the use of seaweed or iodised salt, two potentially concentrated sources of iodine.
Seaweed absorbs iodine from seawater and is an excellent source. Sea vegetables also contain many other minerals and trace minerals, including calcium, copper and magnesium. They can be high in protein and fibre whilst being low in calories and fat-free.
The amount of iodine in seaweed (kombu, nori, arame and wakame) is highly variable. The edible kelp, kombu, used in East Asian cuisine can be extremely high, so avoid using kelp if you have a thyroid problem. Some health bodies advise not eating seaweed more than once a week during pregnancy, as it may contain too much iodine that can disrupt thyroid function. Use sparingly and refer to the nutritional information on the packaging for guidance.
For most people, regular use of small amounts of powdered or crumbled seaweed added to soups, stews, salads, pasta dishes or used as a condiment, is an excellent way to ensure a good iodine intake. A healthy vegan diet containing a wide range of vegetables, with some occasional seaweed and/or iodised salt (used sparingly) should supply sufficient iodine.
The dairy industry is clearly on the back foot as the plant milk market is booming. Iodine may be low in a plant-based diet, but with a sprinkle of seaweed and occasional use of iodised salt, you can continue to avoid cow’s milk and fish and the harmful substances they contain.
Visit www.vivahealth.org.uk for more information – Viva!Health is a part of Viva!, Europe’s largest vegan campaigning organisation.