Enhanced iodine concentrating capacity by the mammary gland in iodine deficient lactating women of an endemic goiter region in Sicily

Iodine balance during pregnancy and lactation was investigated by measuring iodine con-centration in the urine of 11 pregnant women, born and living in a moderately iodine deficient endemic goiter area in Northeastern Sicily, collected during the last week of pregnancy, and between the 5th and 7th day after delivery, and in their milk sampled simultaneously with the urine of their newborns. The results were compared with those obtained on similar samples from 16 euthyroid age-matched nongoitrous women and their offspring from an iodine sufficient area. Urinary iodine concentration in pregnant women from the endemic area (1.28 ± 0.13 gMg/dl, mean ± SE) was significantly lower than that of pregnant women from the iodine sufficient area (3.77 ± 0.57 gMg/dl) (t = 3.56, p < 0.005). The longitudinal measurement of iodine concentration in each nursing woman showed a marked increase (≈90%) when compared with the values obtained during pregnancy in both endemic and control groups (2.32 ± 0.36 and 7.76 ± 2.08 gMg/dl; t = 2.13 p < 0.05, respectively). The slight difference in milk iodine concentration between the endemic (3.25 ± 0.77 gMg/dl) and the control (4.33 ± 0.57 gMg/dl) group was not statistically significant (t = 1.14; p < 0.5, NS). Similarly no difference was found in urinary iodine excretion between the endemic and the control newborn groups (3.41 ± 0.76 and 4.30 ± 0.65 gMg/dl, respectively, t = 0.88 p < 0.1, NS). The similarity between milk and urinary iodine content of newborns in the two areas was in contrast with the greatly different daily iodine intake of the mothers (endemic area 45 ± 6 gMgl/24h vs control area 106 ± 23 gMgl/24h, t = 2.14 p < 0.05 estimated in general population). An explanation for this was given by the calculation of milk iodine uptake (% intake) by the mammary gland, which was higher in endemic as compared with the control group (45 ± 6% vs 34 ± 4%). Enhanced iodine uptake by the mammary gland of the lactating mothers from endemic goiter area in the presence of low iodine supply can account for the above findings. This enhanced concentrating capacity, being inversely related to daily iodine intake (r = -0.41 p < 0.05), appears to be a further effort to effectively compensate for iodine deficiency, in order to prevent congenital hypothyroidism and to correct transient hypothyroidism of the infant.