The iodine concentrations of the milk types are shown in
Table 2. Overall, milk iodine concentration was not affected by
supermarket but was significantly (P < 0.001) influenced by milk
production system with organic and branded organic milk having
lower iodine concentrations than conventional.
Branded organic milk had the lowest mean iodine concentration and this had a tendency
to be lower than own-brand organic (P < 0.059). Overall, the
iodine concentration of organic (including branded organic) milk
was 35.5% lower than conventional. A production system x supermarket interaction (P < 0.05) was seen due to Supermarket 2 having unusually high iodine concentrations in its milk labelled as
organic. If data from this supermarket are excluded the iodine concentration of organic (including branded organic) milk was 43.9% lower than conventional. Interestingly, conventionally produced UHT milk had a lower (P < 0.05) iodine concentration than conventional pasteurised milk with a mean value not significantly different to organic milk. Iodine in Channel Island milk was not significantly different to conventional milk.