We note that there has already been an ALSPAC study showing an effect of fish intake during pregnancy on I.Q in the child. Fish is a rich source of iodine which may, at the very least, have contributed to the beneficial effects of fish observed. Therefore, this project would build on this association and evaluate the link between maternal iodine status during pregnancy and developmental scores in the offspring.

Background

Iodine is essential for the production of thyroid hormones, thyroxine (T4) and triiodityronine (T3). The mother is an important source of thyroid hormones to the developing fetus, particularly in the first trimester before the onset of fetal thyroid function. Thyroid hormones are required for the neurological development of the child.

The recommended intake of iodine in the UK is 140 mcg/day and no increment is recommended during pregnancy. However, more recently the World Health Organisation has advised 250mcg of iodine per day during pregnancy.

Iodine deficiency during pregnancy in the most severe form, leads to development of cretinism in the offspring. However, studies have also demonstrated that mild to moderate maternal iodine deficiency, and the subsequent effect on thyroid hormone concentration, can lead to a spectrum of disorders in the offspring including reduction in psychomotor development, reduction in IQ, and ADHD development.

The recommended method of assessing the adequacy of iodine intake in a population, is through urinary iodine concentration measurements. This is because over 90% of ingested iodine is ultimately excreted in the urine and therefore is a useful biological marker of recent iodine intake.

Historically iodine deficiency was common in several parts of the U.K, and a goitre belt was documented from the West Country up to the Cotswalds and Derbyshire, including the area of Avon. Though the UK is currently considered to be iodine sufficient, the status of iodine in the population is not monitored through urine measurements. Data on iodine from the National Diet and Nutrition Survey is based on food diary analysis, which is not as accurate as urinary measures. However, this indicates that young women (19-24 years) have mean intakes below the RNI and that 12% of this age group of women had intakes less than the lower reference nutrient intake. In addition to the NDNS data, other studies in the UK have measured urinary iodine in pregnant women, which revealed mild to moderate deficiency in some women. We have assessed iodine deficiency in a group of women of childbearing age from the University of Surrey: 33% of the women had an iodine intake below the reference nutrient intake (RNI) and had they become pregnant, 79% of them would have been below the current WHO requirements for pregnancy.

Study proposal:

To date, there are no studies in the UK which assess the impact of mild to moderate maternal iodine deficiency on child (or birth) outcome. It is therefore proposed to use the ALSPAC urine samples to measure iodine status in pregnancy and to link that to the existing ALSPAC data on pregnancy and birth outcomes, IQ and other developmental scores in the offspring. Through the use of the food frequency questionnaires, foods that contribute to iodine status can be evaluated against outcome measures in order to provide practical dietary advice for women during pregnancy.

In order to asses iodine in urine, approximately 1.2 ml of urine would be required from the frozen stored samples. We plan to analyse some 1000 urine samples and the outcomes listed above will be evaluated in the children of the pregnant women studied. (Sarah Bath, my PhD student, could assist in pulling th4 samples from the freezer if that would help.) The food frequency questionnaires would be assessed with particular attention to foods rich in iodine (fish, milk and dairy products) to determine the foods that contribute the most to the iodine status in this group of women.

Selection of urine samples will use that gestation (which should be as near to 12 weeks as possible) for individuals for whom most outcomes are available (especially for IQ at age 8, and where possible WPSSI at age 4).

The urine samples will be analysed in Southampton. Iodine determination will be carried out by ICP-MS.

The statistical analyses will be undertaken by the PhD student, Sarah Bath, under the guidance of Colin Steer.