Iodine Status and Growth in Cow's Milk Allergy
Even mild iodine deficiency can affect school performance, intellectual ability, and work capacity presenting a threat to future social and economic achievement across the world, as demonstrated by Bougma et al (5) who found a 6.9 to 10.2 reduction in intelligent quotient points in iodine-deficient children compared with those that were iodine replete. Global evidence of iodine status is, however, incomplete and limited evidence exists for subgroups of the population who are more at risk, such as those required to exclude cow's milk in their diet. A dietary survey performed in the United Kingdom has found that cow's milk is the main dietary source of iodine and that intake of this mineral is low in many population groups; however, these data are likely to underestimate the scale of the problem in at-risk subgroups such as children with cow's milk protein allergy (CMPA) (6). In children with CMPA, the mainstay of treatment is the complete avoidance of cow's milk and its derivatives and where breast milk is not available for infants, a suitable hypoallergenic formula is used (7). The iodine content of infant formula in the EU, which includes hypoallergenic formula, is closely regulated by the 2014 European Directive (8) and must be between 15 and 50 μg/100 kcal (equivalent to 6.5–32.5 μg/100 mL) with an adequate intake for this age group of 70 μg/day.
Thomassen et al (9) published an observational study that for the first time highlights the relation between CMPA in children on exclusion diets, iodine status, and growth. The cohort included 57 Norwegian children younger than 2 years with suspected CMPA (based on symptom relief following cow's milk protein exclusion) who were either completely breast-fed, partially breast-fed, and supplemented with hypoallergenic formulas or weaned onto solids. All had been on a cow's milk protein elimination diet for a minimum of 3 weeks. Two spot urine samples, 3-day diet diaries and food frequency questionnaires were used to analyse iodine status and intake and growth parameters were taken at birth and during the study.
In this cohort 57% of children were breast-fed (24% mainly and 33% partially) and 69% had hypoallergenic formula and were weaned. Within the pooled cohort, there was a large range in urinary iodine content (UIC), with a median content of 159 μg/L; however, more than 30% of children were found to be iodine deficient (<100 μg/L as defined by the World Health Organization (3)). The present study found that children with CMPA who were mainly breast-fed had a higher risk of iodine deficiency with a median UIC of 86 μg/L and a prevalence of deficiency of 58% compared with those who were fed a combination diet (breast milk and hypoallergenic formula) or weaned diet (median UIC content 172 and 175 μg/L, respectively and risk of deficiency 12% and 32%, respectively).