Iodine content in milk from German cows and in human milk: new monitoring study

Objective: Milk can provide more than 1/3 of the iodine content in hu- man diet. Moreover, iodine supply in cow's milk in Germany has improved throughout the last decade. Since 1982, analyses of io- dine content of cow's and human milk have been undertaken regularly in the State of Thuringia (East Germany). Data show in- creasing iodine concentration in milk over the past few years. Nonetheless, dietary sup- ply of iodine via milk needs to be continu- ously monitored. Material and methods: To investigate the latest trend of iodine content in milk over time, 135 samples of cow's milk and 65 samples of human milk were ana- lyzed by ICP-MS after digestion with tetra- methyl-ammonium hydroxide. Samples of cow's milk (conventionally and organically produced) were purchased from the same supermarkets in Thuringia in March and No- vember every year between 2007 and 2011. Human milk samples were obtained on a vol- untary basis from breast-feeding women in Thuringia during the same time period. Re- sults: Samples of cow's milk from 2007 to 2011 showed a mean iodine concentration of 122.0 ± 36.8 µg/l. There was no significant change during these 5 years (p > 0.05). In the same period, iodine content of conven- tionally produced milk was on average 51 µg/l higher compared to organically pro- duced milk (p < 0.001). For all human milk samples, the mean iodine content was 170 ± 96 µg/l, with a range of 45.6 - 478.4 µg/l. In breast milk, not only were high variations present between samples of milk from the individual women, but iodine content also varied over lactation time. Conclusions: The current results demonstrate that in East Ger- many the average iodine content in cow's milk has remained stable at an appropriate level during the last 5 years. Although io- dine concentrations in human milk likewise reveal relatively constant values on average, individual variations can be substantial.