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Iodine and the Thyroid

Iodine and the Thyroid. Mark Vanderpump UK National Coordinator Iodine Global Network. Thyroid gland. Retina. Brain. Pituitary. Inner ear. Heart. Spleen. Liver. Gut. Bone. Muscle. Thyroid hormone target tissues. Thyroid hormones act everywhere. Basal metabolic rate

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Iodine and the Thyroid

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  1. Iodine and the Thyroid Mark Vanderpump UK National Coordinator Iodine Global Network

  2. Thyroid gland

  3. Retina Brain Pituitary Inner ear Heart Spleen Liver Gut Bone Muscle Thyroid hormone target tissues Thyroid hormones act everywhere Basal metabolic rate Growth and development Temperature regulation Fat production Blood vessels Skin Hair Bone marrow Kidney Lung

  4. Thyroid hormones

  5. Thyroid hormone biosynthesis

  6. Iodine • An important element in the manufacture of thyroid hormones • Most iodine is present in sea water which evaporates and returns to the soil in rain • Low iodine levels are common in mountainous regions far away from the sea • The major source is bread and milk

  7. Iodine deficiency disorders • Fetus: abortion, stillbirth, congenital anomalies, perinatal mortality, endemic cretinism • Neonate: goitre, hypothyroidism, mental retardation • Child: goitre, (subclinical hypothyroidism), impaired mental function, delayed physical development • Adults: goitre, hypothyroidism, impaired mental function, spontaneous hyperthyroidism, iodine-induced hyperthyroidism

  8. Criteria for assessing iodine nutrition(WHO, 2007)

  9. Severe iodine deficiency in pregnancy and neurodevelopment Northern Himalayas (n=4000) Goitre 92% and hypothyroidism 40% Iodised oil shrunk goitres and reversed symptoms and signs of hypothyroidism No cretins or deaf mutes born despite previous incidence 20-25% (Ibbertson, 1971)

  10. Severe iodine deficiency inpregnancy and neurodevelopment Papua New Guinea (n=160,000) Placebo-controlled trial of iodised oil injections pre-conception or early pregnancy Reduced incidence of cretinism and improved motor/cognitive function (Pharoah et al, 1971)

  11. The Bronchocele(Prosser, 1769) ‘A tumour arising on the fore-part of the neck. It generally first appears sometime betwixt the age of eight and twelve years, and continues gradually to increase for three, four, or five years; and often the last half-year of this time, it grows more than it had for a year or two before.’ ‘It very rarely happens to boys, indeed I have never been able to make out one instance of it, in a man or boy.’ ‘It is very common in many counties in England, Derbyshire especially, where from its frequency it has the name of Derby Neck, and some other countries are almost free from it.’ ‘This disease….affects the inhabitants about the Alps, and other parts of Italy.’

  12. The present state of Derbyshire (Pilkington, 1789) “There is one disease to which the inhabitants of Derbyshire are so much subject, that it has taken its name from its great prevalence in this situation." Some thought it was hereditary, others that it was caused by living "on the bleak sides of hills." They all agreed that women, particularly "child-bearing poor women" were the main victims of "this very unfortunate female disease.“

  13. UK iodine status: Early studies • 1924 survey of 375,000 schoolchildren in England and Wales: Visible goitre in 30% • 1948 MRC survey: Visible goitre in 50% adult women in Oxford, 43% girls in Dorset, 26% of children in St Albans, 2% in Essex • 1958 repeat MRC survey: Goitre prevalence in girls in Oxford from 40% from 27% • 1963-66: Goitre in Sheffield (12% men, 25% women), E Lothian (0.3% men and 4% women), Durham (1% men, 9% women)

  14. “Accidental public health triumph”(Phillips, 1997) • Rise in iodine content of milk especially winter • Changes in UK farming practice from 1940s with iodine-rich artificial feeds/disinfectants • UK governments post WWII encouraged compulsory milk consumption in schools • Iodine content of milk alone sufficient to meet recommended daily requirement 150µg

  15. UK iodine status: Later studies • 1990: Thyroid enlargement no longer detectable in schoolchildren in South Wales • 1994: Median UIC 102µg/g in NE England • National monitoring aimed to avoid concerns re iodine toxicity not deficiency • 2002-2009: 50% of pregnant women in small surveys (Middlesbrough, Dundee, Cardiff, Guildford) median UI 66µg/L • 2006: Iodine deficiency in pregnant women in Ireland especially in summer months • 2007: Survey of 36 household salt preparations in supermarkets for iodine – sufficient in only 2 (Lazarus & Smythe)

  16. UK iodine statusA national survey Generously supported by Clinical Endocrinology Trust

  17. UI concentrations in UK schoolgirls (n=737) Median 80µg/L

  18. Summer Urine samples n=537 Median 76µg/L Winter Urine samples n=200 Median 95µg/L P<0.001 Aberdeen 82µg/L Newcastle/ Gateshead 75µg/L Belfast 62µg/L Birmingham 75µg/L London 85µg/L Cardiff 80µg/L Exeter 83µg/L

  19. UK iodine survey: Milk intake

  20. National iodine status based on UI in schoolchildren(WHO 2011)

  21. Impact of mild-moderate iodine deficiency • Hypothyroxinaemia not raised serum TSH • Maternal T4 crucial before 13 weeks gestation • Children born to women may have psycho-neurological deficits and delayed mental function compared with controls • Functional consequences in older children is unclear

  22. How to correct iodine deficiency? • Salt iodisation is safe, equitable, self-financing and extremely cost-effective • Mandatory bread salt iodisation in NZ and Australia has increased iodine intake • Oral potassium iodide supplements for most susceptible groups eg women pre-pregnancy

  23. Iodine status in industrialised countries • Strong public health objective to lower salt intake to reduce risk of hypertension • 10% of UK salt intake is added to food at table • Cow’s milk intake up to 50% and although UK milk iodine stable (300mcg/l) but evidence consumption falling • Dialogue with food/salt industries ?feasibility of adding iodised salt to processed foods • How provide reassurance at population level?

  24. Iodine awareness in UK(Combet et al, 2015) • Recent study of 1026 pregnant or recent post-partum women in Glasgow • Nutritional recommendations 96% • Iodine specific recommendations 16% • Identification of milk as source 9% • 50% of UK pregnancies unplanned

  25. Conclusions • UK is example of increase in mild-moderate iodine deficiency in industrialised countries • Mild perturbations of fetal and maternal thyroid function have impact upon neurodevelopment and potential impact in older children • Iodine supplementation is required in mild-moderate iodine deficiency • Variation in UI in different population groups with young women most vulnerable group • How can this group be targeted with a population-based intervention?

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