The mean concentration of iodine in the milk rose from 1991 (117 37 mg/L) to 2008
(259 58 mg/L) (P < 0.001). The iodine concentration was greater in skimmed milk (273 52 mg/L) than
in semi-skimmed milk (254 57 mg/L) or whole milk (251 61 mg/L) (P < 0.0001). The winter samples
had a greater concentration of iodine (270 55 mg/L) than the summer samples (247 58 mg/L)
(P < 0.0001), independently of the type of milk. The urinary iodine concentrations in all three epidemiologic
studies were significantly associated with the frequency of milk intake.
Conclusions: The concentration of iodine in cow’s milk has risen over recent years, and it is higher in
skimmed milk. The results also show that cow’s milk is a relevant source of dietary iodine.