Iodine is widely known for its vital role in the production of thyroid hormones. But its effects are far reaching – iodine deficiency has been linked to heart disease, cognitive impairment, obesity and some forms of cancer . According to the World Health Organisation (WHO), over 56% of Europeans are deficient in iodine. A deficiency in iodine negatively affects every stage of human development and impairs the function of our brain and physical development (particularly critical for foetal development and early growth). For women who are pregnant or planning a pregnancy, adequate iodine is required to prevent impaired foetal neurological development. However, some research shows that because the breast glands concentrate iodine and the newborn may still get sufficient iodine through breast milk even if the mother is deficient. During childhood, iodine deficiency may impair growth, cognitive function and even motor function.
Iodine and Thyroid Health
Thyroid hormones (T4, aka thyroxine and T3), produced by the thyroid gland are made from iodine and the amino acid tyrosine which is a non-essential amino acid ie our bodies can normally produce it on our own.
Certain foods in our diet called goitrogens can interfere with thyroid metabolism by combining with iodine and disrupting iodine uptake in the thyroid gland. This can aggravate the effect of iodine deficiency. Goitrogens include cruciferous vegetables like cabbage, kale, broccoli, turnips, cauliflower, cassava which are highly nutritious but goitrogens are inactivated once cooked. In general, these goitrogenic foods do not have a major clinical effect unless there is an existing iodine deficiency.
In women with sub-clinical hypothyroidism, there is higher risk of atherosclerotic disease due to the impact of thyroid hormones on lipid profiles and lipoprotein a (LP(a)), a risk factor for cardiovascular disease.
Iodine and Cancer
A 2017 study in the Journal of Cancer suggested that an explanation for the exceptionally low incidence of breast cancer in Japanese women was due to the increased consumption of iodine in their diet. Interestingly, Japanese women who then adopted a Western diet showed a higher incidence of breast cancer. Iodine is required for healthy breast tissue development and is thought to suppress breast cancer cell growth.
Iodine deficiency is also associated with fibrocystic breast disease which affects over half of women of child-bearing risk and is associated with an increased risk of breast cancer.
Increasing dietary iodine
Iodine is a relatively scarce mineral but it is abundant in our oceans. Our soil today is increasingly stripped of vital minerals (due to modern intensive agriculture) compared to decades ago. As a result, it is getting harder to consume sufficient quantities of iodine. If you are concerned about iodine insufficiency, ensure your diet includes seaweed (a very rich source) , saltwater fish such as cod or eggs.