First-month variations in total iodine content of human breast milks.

In 183 samples of breast milk from 23 young mothers we found the mean total iodine content to be 47 ng/ml, a value that is not dependent on length of gestation. There is a progressive increase in iodine concentration from colostrum to transitional and mature milk. The results show that breast milk sometimes contains an amount of iodine barely necessary to make thyroid hormones, which is around 10 micrograms in the first days of life rising to about 15-20 micrograms after four weeks. Secondly, nursing mothers should be watched, because if their daily breast milk contains more than 50 micrograms iodine for several consecutive days, they may be on a negative balance.