Iodine is an essential trace nutrient for all infants that a normal component of breastmilk. Recommendations for maternal intake during lactation by various organizations range between 150 and 290 mcg daily. Infant requirements are estimated to be 15 mcg/kg daily in full-term infants and 30 mcg/kg daily in premature infants. The use of excessive amounts of iodine in the mother near term and during breastfeeding can increase breastmilk iodine levels and cause transient hypothyroidism in breastfed infants. The absorption of iodine can be marked after application to open wounds or mucous membranes. Exposure of mothers to iodine who are or will be breastfeeding should be avoided or minimized to the extent possible by avoiding its use on maternal mucous membranes (e.g., vaginal use, wound therapy), avoiding prolonged contact time, avoiding repeated applications, and applying it to the smallest possible surface areas of the body. It is possible that maternal exposure to iodine near term could interfere with thyroid studies done as a part of newborn screening tests.
Iodine is a normal mineral in breastmilk that is essential for the infant's thyroid. The amounts of iodine in breastmilk vary with maternal iodine intake. A 1981-82 survey of 61 breastmilk samples from 37 women in North Carolina found a mean iodine concentration of 178 mcg/L (range 29 to 490 mcg/L). A 2002-06 survey of 57 women in the Boston area found a similar mean concentration of 205 mcg/L (range 2.7 to 1968 mcg/L) and a median iodine breastmilk concentration of 157 mcg/L.
A study of 36 breastmilk samples from 18 different states in 2003-04 found a mean iodide breastmilk concentrations of 63.3 mcg/L (range 4.5 to 162 mcg/L). Another study of 108 breastmilk samples from 10 women by the same authors found a mean iodide concentration of 87.9 mcg/L (range 3.1-334 mcg/L), and a median concentration of 55.2 mcg/L. The reason for the differences in iodine values between these two studies and the above studies is not clear.
Two women were givenpotassiumiodide orally. One was given 325 mg orally 3 times daily to a total of 3.6 grams and the other was given 650 mg orally 3 times daily to a total of 4.6 grams. Milk samples were obtained after the eighth and eleventh doses in the first woman and 2 hours after the last dose in the second woman. The first woman had milk iodide concentrations of about 33 and 29 mg/L and the second had a concentration of about 38 mg/L. The analytic method used in this old study was insensitive and imprecise by modern standards.
A woman developed an abdominal wall abscess 1 week after having a cesarean section. The abscess was treated with systemic antibiotics and the wound was packed with 60 sq. cm of iodine tampons, containing about 10.5 mg of iodine. On day 29 postpartum, her milk iodine was 4410 mcg/L (normal range 29 to 490 mcg/L). Her iodine therapy was stopped, and 2 days later milk iodine was about 1400 mcg/L; by day 40 postpartum, it was about 1000 mcg/L. By day 60 postpartum, the milk level was below 100 mcg/L.
The mother of a 31-week preterm infant packed her cesarean section wound with iodine-soaked gauze because of wound dehiscence and infection. Her breastmilk iodine concentration at 3 weeks postpartum was 1911 mcg/L (upper limit of normal 185 mcg/L).
The mothers of 31 preterm Korean infants was measured for iodine concentration on week 1, 3 and 6 postpartum. Korean mothers have elevated iodine levels from large amounts of dietary iodine in brown seaweed soup during the first month postpartum. Median breastmilk iodine levels were 2529, 1153 and 822 mcg/L at the 3 times, respectively.
A mother used an iodine antiseptic on her episiotomy wound for 10 to 12 days postpartum. At 15 days postpartum, her milk iodine level was 300 mcg/L (normal 100-200 mcg/L).
A mother ate large amounts of seaweed soup imported from China for the first 10 days postpartum to increase her breastmilk supply. Breastmilk iodine levels were much higher during the time of seaweed consumption at 878 mcg/L total iodine compared to 188 mcg/L 4 weeks later and 144 mcg/L 7 weeks later.
A study in northern Spain compared the milk iodide level of mothers taking a normal diet, including iodized salt and seafood (n = 14), with mothers on the same diet plus a supplement of 200 mg daily ofpotassiumiodide (n = 46). The median breastmilk iodide levels from supplemented mothers of preterm infants was 0.172 mg/L in the supplemented mothers compared to 0.128 mg/L in the unsupplemented mothers. The median breastmilk iodide levels from supplemented mothers of fullterm infants was 0.178 mg/L in the supplemented mothers compared to 0.117 mg/L in the unsupplemented mothers. No statistical difference was found between preterm and fullterm milk iodide in either the supplemented or unsupplemented group. The authors conclude that in this iodine-sufficient area, unsupplemented mothers excrete sufficient amounts of iodide in breastmilk.
Sixteen lactating women were administered 752 mcg ofpotassiumiodide (572 mcg iodine) in the morning afer an overnight fast. They also ingested an additional 36 to 685 mcg of dietary iodine during the study period. Breastmilk samples were obtained at baseline and every hour for 8 hours. Breastmilk iodide increased from an average of 46 mcg/L at baseline to a peak of 354 mcg/L. Peak iodine levels in milk occurred at an median of 6 hours (range 5 to 7 hours) after the dose of iodine.
The preterm infants of Korean mothers with high levels of breastmilk iodine had relative high urinary iodine levels that were thought to be related to high maternal intake of iodine.
A woman developed an abdominal wall abscess 1 week after having a cesarean section. The abscess was treated with systemic antibiotics and the wound was packed with 60 sq. cm of iodine tampons, containing about 10.5 mg of iodine. On day 29 postpartum, her breastfed infant's urine contained 3932 mcg/L of iodine (normal range <185 mcg/l).="" by="" day="" 40="" postpartum,="" the="" infant's="" urine="" iodine="" level="" was="">185>
The mother of a 31-week preterm infant packed her cesarean section wound with iodine-soaked gauze because of wound dehiscence and infection. The urine iodine level of her 2-week-old breastfed neonate was 684 mcg/L (normal range 42-350 mcg/L).
A mother used an iodine antiseptic on her episiotomy wound for 10 to 12 days postpartum. At 15 days of age, her infant had a urinary iodine concentration of 410 mcg/L (normal 100 to 200 mcg/L).
Two mothers originally from Asia (Korea and China) reportedly ate large amounts of soup made from seaweed from their home countries in the postpartum period. The infants of both mothers had elevated urinary iodine levels. The Korean mother continued to eat the soup for several weeks postpartum. Her infant's urinary iodine levels were 391 mcg/L and 690 mcg/L (normal range 100 to 300 mcg/L) at 1 and 2 months postpartum. The Chinese mother ate large quantities of seaweed soup for the first 10 days postpartum to increase her breastmilk supply. Her infant's urinary iodine level at 4 weeks of age was 343 mcg/L or 5055 mcg/gram of creatinine (normal range 100 to 300 mcg/gram).
A study of 46 nursing mothers supplemented with 200 mg ofpotassiumiodide daily measured the iodine content of their breastfed infants' urine. Urine iodide concentrations were 0.365 mg/L among preterm infants and 0.376 mg/L among fullterm infants.
Effects in Breastfed Infants:
In Switzerland, a girl born at 29 weeks of gestation with adequate size for gestational age showed negative TSH screening on day 5. Her mother developed an abscess of the abdominal wall 1 week after her cesarian section and the wound was packed with tampons containing about 10.5 mg of iodine. The baby's TSH was elevated to 23 milliunits/L on day 23, and 288 milliunits/L on day 29. Free thyroxine (T4) levels were decreased to 2.8 ng/L and free liothyronine (T3) with 1.52 ng/L, without signs or symptoms of hypothyroidism. Iodine contents of maternal milk and of infant urine were 4.4 mg/L and 3.9 mg/L, respectively. Treatment with levothyroxine was started, breastfeeding was discontinued and disinfection with iodine was stopped. The infant's thyroid function tests normalized after 6 days. The infant's abnormal thyroid function tests were probably caused by maternal iodine use.
The mother of a 31-week, 961 gram preterm infant packed her cesarean section wound with iodine-soaked gauze because of wound dehiscence and infection. She was expressing milk for her hospitalized infant. The infant's thyroid function tests were normal at birth, but at 2 weeks of age, the infant's serum thyroxine was borderline low and TSH levels were elevated. One week later, TSH had increased to 77 milliunits/L and both thyroxine and free thyroxine levels were low. Breastmilk was discontinued and levothyroxine was started. The mother discontinued the iodine packing and 1 week later breastmilk feeding was resumed. At 2 months of age, the infant's thyroid function test were normal while taking levothyroxine.
A study of 31 preterm infants born at 34 weeks gestational age or less was performed in Korea where mothers typically ingest large amounts of seaweed soup during the first month postpartum. Subclinical hypothyroidism was frequently found in the infants with high intake of iodine from breastmilk.
A mother used an iodine antiseptic on her episiotomy wound for 10 to 12 days postpartum. At 15 days of age, her infant had elevated TSH and low free T4 serum levels, an enlarged thyroid gland, and an elevated urinary iodine concentration. The infant's symptoms were probably related to maternal iodine application.
Two mothers originally from Asia (Korea and China) reportedly ate large amounts of soup made from seaweed from their home countries in the postpartum period. Their infants had elevated thyrotropin (TSH) levels when tested at 3 to 4 weeks of age and signs of hypothyroidism. Both were treated with thyroid hormones and regained normal thyroid function.
Possible Effects on Lactation:
Relevant published information was not found as of the revision date.
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