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Interested in iodine and thyroid function? - 13/01/2004
 
VEGA raises some issues in a letter to The Lancet

The Editor
THE LANCET
32 Jamestown Road
London
NW1 7BY

14th April 2003,


Sir,

Monitoring iodine deficiency in the UK

Vitti and colleagues (April 5, p 1226) include the UK among iodine-sufficient countries. However, significant populations within the UK with various dietary aversions may be threatened with deficiency because of allergies, food-intolerances or vegetarian and vegan persuasions. Current “sufficiency” in the dietary iodine supply in the UK may be attributed to “silent prophylaxis”: milk and animal- and fish-derived products are the main iodine sources, being haphazard supplementation at one remove from fortified feeds given to farm animals to stimulate production and residues of iodophors used to disinfect mucky teats and udders and dairy machinery. Iodine levels fluctuate seasonally, being higher in winter milk and its derivatives when the cows are housed and fed on greater quantities of concentrates. Hypoiodism is not an uncommon cause of illthrift and lowered fertility in British grazing animals, for which vets are prepared to administer supplements.

Little iodised salt is used in human diets in the UK and is not readily available for table use or cooking or among the ingredients in manufactured commodities; sea-salt contains very little iodine. Drinking water is a very poor source of iodine: supplies are not even routinely monitored for this purpose.

Over the last 10 years, partly in collaboration with the then MAFF, we have been assessing the iodine (and selenium) and thyroid status of populations with aversions, for various reasons, to dairy products and other animal- and fish-derived commodities, using dietary surveys, recourse to suitable supplementation, and urine analyses. These surveys have acquired a national significance, especially for women of childbearing age and the checks made when they are assessed at antenatal bookings. Iodine intakes need to be raised to ensure satisfactory gestation and delivery of a baby with a well-developed brain and a prognosis of cognitive competence and favourable prospects in learning and behaviour.

Our research has also shown that individuals who consume certain seaweeds may have daily iodine intakes approaching or exceeding the provisional maximum tolerable daily intake (PMTDI)2 of 1000 mcg. Concentrations of iodide in seawater are very low, but seaweeds possess the means of concentrating iodine even to toxic levels and with adverse environmental consequences; terrestrial plants lack the capability to “mine” soils. Seaweeds are minor components of British diets, although eligible to be included in the initiatives to stimulate consumption of fruit and vegetables. We are urging retailers to increase information on the nutritional value and application of commercially-available seaweed products. Health food manufacturers have increased the monitoring of kelp tablets after we and the MAFF discovered wide discrepancies of content displayed on labels – in one instance a dangerous excess up to nearly 10 times the declared value. The trade also gives assurances of low contents of heavy metals in these products.

Dietary aversions accompanied by extreme consumption of some plant-foods, such as soya and cruciferous vegetables with goitrogenic activity, may exacerbate the effect of iodine deficiency in some regimens.

We advocate modest fortification (with iodide or iodate) and appropriate labelling of alternative choices for the significant and increasing population of meat-reducers and dairy-frees, for whom recommendations on intakes of iodised salt would tangle with general recommendations to the public and the food-industry to reduce use and consumption of salt. (Recommended nutrient intakes for adults are 150mcg and 200mcg for pregnant and lactating women; regular daily intakes above 1000mcg are to be avoided. Contents, per 100g, of some major dietary sources of iodine are (in mcg): mackerel 140; cod 110; “vegetarian” cheddar cheese 26; whole or semi-skimmed milk 20 (summer), 41 (winter); human milk 7. 6gm of iodised salt furnishes about 120mcg of iodine). We also recommend doctors appraising TSH and T4 results to consider overlooked dietary issues before resorting to prolonged courses of thyroxine for their patients.


References

Vitti P, Delange F, Pinchera A, Zimmermann M, Dunn JT. Europe is iodine deficient. Lancet 2003; 361: 1226

Lightowler HJ, Davies GJ. Iodine intake and iodine deficiency in Vegans as assessed by the duplicate-portion technique and urinary iodine excretion. Br J Nutr 1998; 80: 529-535

Department of Health. Dietary Reference Values for Food Energy and Nutrients for the United Kingdom. London: HMSO, 1991

Food Standards Agency. McCance and Widdowson’s The Composition of Foods, Sixth summary edition. Cambridge: Royal Society of Chemistry, 2002

Yours

Helen Lightowler
Nutrition and Food Science Group,
School of Biological and Molecular Sciences,
Oxford Brookes University,
Oxford,
OX3 0BP
UK

Alan Long
VEGA Research (Vegetarian Economy and Green Agriculture),
14 Woodland Rise,
Greenford,
UB6 0RD
UK
Email: info@vegaresearch.org
 
 
 

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