When we think of hunger, we think of the gaunt and emaciated children in sub-Saharan Africa. There is another form of hunger known as “hidden hunger” which requires the services of a biochemist to detect deficiency symptoms in blood or urine and the three main nutrients of hunger are iron, leading to anaemia, vitamin A leading to blindness and iodine, leading to goiter. Today’s blog focuses on the latter. Iodine is required as an element within the molecular structure of the thyroid hormone and this hormone plays an essential role in every cell where it regulates metabolic rate. Iodine also has a major role in brain development during pregnancy and the very early years of life. If iodine intakes are inadequate, a condition known as goiter emerges in which the thyroid gland in the neck swells as it seeks to extract every last drop of iodine in blood for thyroid hormone synthesis. Most importantly, iodine deficiency in pregnancy will lead to impaired cognitive ability and if severe will lead to severe mental retardation, a condition known as cretinism.
Iodine is a rare element in the earth’s crust and is highly water-soluble and is thus concentrated in the oceans. It is deposited on land as rainwater and the further the distance from the sea, the lower the impact of this iodine rich rainfall. Inland mountainous regions are particularly susceptible to low soil iodine levels as rainwater and streams wash the iodine away, returning it to the sea. Thus there are large tracts of land known as goiter belts where soil iodine is sufficiently low to create a high prevalence of goiter. Iodine deficiency remains one of the great global nutritional challenges with the WHO estimating that 1.9 billion, almost one third of humanity, had inadequate intakes of iodine over the period 1994 to 2006 with approximately 20 million cases of impaired mental function. Great progress has been made in reducing this figure through the fortification of salt with iodine. In contrast to the improving situation in developing countries, inadequate iodine intake is now becoming an issue in developed countries.
Without any planned intervention, the problem of inadequate iodine intakes in certain developed countries was considerably reduced from the 1960s onwards because of the introduction of iodized cleansing substances (iodophors) into modern milking parlour and also the introduction of iodine enriched salt licks to ensure adequate iodine intake by dairy cows. Milk became on of the main sources of iodine and milk consumption was encouraged particularly in children. However, the use of iodophor sanitizing agents in dairy farming has declined dramatically in recent times and the use of table salt, including iodized salt, has fallen, given the negative nutritional messages about salt and health. In a recent survey of the iodine status of UK schoolgirls using urinary iodine levels, 51% were deemed to have mild iodine deficiency, 16% had moderate deficiency and 1% had severe deficiency. Just about one third had adequate iodine status. The UK is now ranked eighth in the top ten of iodine deficiency countries according to the International Council for Control of Iodine Deficiency Disorders. Two studies have shown that if young children with poor nutritional status receive iodine supplements, their cognitive function rises significantly.
From a nutrition policy point of view, the issue of iodine adequacy is of greatest importance in women of childbearing age. The method used to assess the iodine status in populations is to take a single urine sample with the average value being compared to a WHO reference range for mild, moderate and severe iodine deficiency. However, whereas that approach can tell us if a population overall has a problem with iodine status, it cannot tell us who within that population has a true problem. A recent paper has shown that 10 different urine samples from one individual are needed to assess an individual’s iodine status. Thus at present, there is a need to ensure that all women of childbearing age receive adequate iodine intake. If, as the data would indicate, inadequate iodine status is such a serious issue especially as it relates to early life cognitive function, then iodine must become a very important public health nutrition issue.
Ironically, the many pregnant women who shift to organic foods in the belief that this will help ensure as healthy a baby as possible, will see a very significant fall in iodine intake. Organic animal production greatly restricts the use of mineral and vitamin supplements in animal feeds. Recent survey of the iodine content of milk from organic and conventional farms shows that the organic milk is 42% lower in iodine than conventional milk, and milk accounts for almost half the UK iodine intake. In fact, pregnant women should be counseled to avoid organic milk.