Transcript Powerpoint - Iodine Global Network

Iodine and the Thyroid
Mark Vanderpump
UK National Coordinator
Iodine Global Network
Thyroid gland
Thyroid hormone target tissues
Retina
Pituitary
Thyroid hormones act
everywhere
Heart
Liver
Basal metabolic rate
Growth and development
Temperature regulation
Fat production
Blood vessels
Skin
Hair
Bone marrow
Kidney
Lung
Brain
Inner ear
Spleen
Gut
Bone
Muscle
Thyroid hormones
Thyroid hormone biosynthesis
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
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, iodineinduced hyperthyroidism
Criteria for assessing iodine nutrition
(WHO, 2007)
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)
Severe iodine deficiency in
pregnancy 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)
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.’
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.“
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)
“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
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)
UK iodine status
A national survey
Generously supported by
Clinical Endocrinology Trust
UI concentrations in UK schoolgirls
(n=737)
%
Median 80µg/L
Summer
Urine samples n=537
Median 76µg/L
Aberdeen 82µg/L
Winter
Urine samples n=200
Median 95µg/L
Belfast 62µg/L
Newcastle/
Gateshead 75µg/L
P<0.001
Birmingham 75µg/L
Cardiff 80µg/L London 85µg/L
Exeter 83µg/L
UK iodine survey: Milk intake
National iodine status based on
UI in schoolchildren
(WHO 2011)
Impact of mild-moderate iodine
deficiency
• Hypothyroxinaemia not raised serum TSH
• Maternal T4 crucial before 13 weeks gestation
• Children born to women may have psychoneurological deficits and delayed mental
function compared with controls
• Functional consequences in older children is
unclear
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
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?
Iodine awareness in UK
(Combet et al, 2015)
• Recent study of 1026 pregnant or recent postpartum women in Glasgow
• Nutritional recommendations 96%
• Iodine specific recommendations 16%
• Identification of milk as source 9%
• 50% of UK pregnancies unplanned
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 mildmoderate 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?