Breast Milk Iodine Concentration (BMIC) as a Biomarker of Iodine Status in Lactating Women and Children <2 Years of Age: A Systematic Review

Abstract

Background: Iodine is needed for the production of thyroid hormones, which are essential for infant growth and development. Given that there are wide variations in breast milk iodine concentration (BMIC) and urinary iodine concentration (UIC), it is unclear if BMIC is associated with UIC in populations residing in iodine sufficient or deficient areas. Aim: To investigate if BMIC can be used as a biomarker for iodine status in lactating women and children &lt;2 years of age. Methods: Electronic databases; PubMed, Web of Science and Scopus were searched until year 2021, for studies investigating the relationship between BMIC and UIC. Studies were reviewed for eligibility, according to inclusion and exclusion criteria, followed by data extraction, according to the PRISMA guidelines. Results: Overall, 51 studies met the criteria for inclusion in the systematic review. BMIC ranged from 18 to 1153 µg/L. In iodine-deficient and iodine-sufficient lactating women, BMIC ranged from 26 to 185 µg/L and 15 to 1006 µg/L, respectively. In most studies, the categorisation of iodine status assessed by median UIC was consistent with the categorisation of iodine status assessed by median BMIC cut off of ≥100 µg/L, to determine iodine sufficiency in lactating women and children &lt;2 years of age. Conclusions: The systematic review indicated that BMIC is a promising biomarker of iodine status in lactating women and children &lt;2 years of age. However, these data need to be interpreted cautiously, given the study limitations in the included studies. Future studies should consider investigating the optimal median BMIC, as there is a lack of high-quality observational and intervention studies in lactating women and infants.

Assessment of Iodine Concentration in Human Milk from Donors: Implications for Preterm Infants

“…In our study, with a median UIC of 112.41 µg/L and a median DHMIC of 148.48 µg/L we might assume an adequate iodine status of the recruited donors. Although there is currently no well-established cut-off point for setting iodine status by BMIC, in most studies the categorization of iodine status assessed by the median UIC was consistent with the categorization of iodine status assessed by the median BMIC cut off of 100 µg/L for determining iodine sufficiency in lactating women [ 30 ].…”

“…For the assessment of the iodine status of our milk donor’s population, a median UIC ≥ 100 µg/L [ 29 ] and a median DHMIC ≥ 100 mcg/L were considered an adequate iodine nutrition [ 6 , 30 ].…”

Prevalence of thyroid dysfunction in neonates receiving parenteral nutrition in the intensive care unit

“…19 Also, the lactating woman's iodine status can influence children's iodine status, whereas lactating women with iodine deficiency (breast milk content < 100 mcg/L) contributed to a reduced urinary iodine content in infants (< 100 mcg/L). 19 …”

Biomarkers of Micronutrients and Phytonutrients and Their Application in Epidemiological Studies

“…During pregnancy, dietary requirements for iodine increase by 50% to 250 µg/d due to the increased production of thyroid hormones required by the mother and her fetus [ 35 ], low thyroid hormone levels may result in a variety of negative effects, notably on brain growth and development, making it worth considering specific assessment for pregnant women iodine status. Postulated pathways for how iodine shortage affects growth may involve decreased levels of insulin-like growth factor 1 (IGF-1) and IGF binding protein 3 (IGFBP-3).…”