Title, Date of Publication & Journal

“Effect of inadequate iodine status in UK pregnant women on cognitive outcomes in their children: results from the Avon Longitudinal Study of Parents and Children (ALSPAC)”

22 May 2013, The Lancet

Claim supported by evidence?

The observational study demonstrates an association between poor iodine status during early gestation and lower child IQ at age 8 to 9 in the UK. As discussed by the authors this is an observational study and association does not imply causation. However, the authors suggest that iodine deficiency in pregnant women in the UK should be treated as an important public health issue that needs urgent attention.

Summary

• The ALSPAC study involved all pregnant women living in Avon district in 1991/92, recording socioeconomic and pregnancy related information took place as well as the storing of maternal urine samples. The paper is based on a retrospective analysis of the iodine content of first trimester urine samples and relating these to offspring IQ scores at ages 8 and 9.
• Two-thirds of pregnant women in the Avon district of the UK during 1991/2 were under the WHO criteria for adequate iodine during pregnancy.
• Those children born to mothers below this limit of 150 μg/g showed demonstrably poorer cognitive function in a series of tests.

Study Conclusions

The results suggest that in this area of the UK, where traditionally iodine deficiency was a problem, iodine consumption during pregnancy remains an issue.

The major source of iodine in the UK is dairy products, so there may be parts of the community where low dairy intake will require special attention.

Strengths/Limitations

This is a well carried out study which is described clearly. All reasonable methods have been used to control variation and reduce bias.

The use of spot urine samples rather than full 24 hour voided samples is standard practice when storing urine for possible unknown future use. Iodine values were scaled using creatinine values to provide scores as μg/g rather than μg/L. The WHO recommended adequate iodine level for pregnant women was interpreted as 150 μg/g. This procedure reduced the within-subject variability, although introduced the unlikely possibility that creatinine rather than iodine concentration is the important factor.

As discussed by the authors this is an observational study and association does not imply causation.

However it is known that extreme iodine deficiency leads to cretinism and other neuro-developmental problems.

A systematic change in the urine samples during storage could explain the apparent lower than expected average iodine status of these mothers. A simple prospective small study using 24 hour voided samples could easily confirm or otherwise the issue as a current public health problem.