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Breast Milk Rubidium and other Trace Elements are Associated with Neurocognitive Development in Infants at Age of 8 Months.

BACKGROUND
Trace elements may affect neuro-development. There is a lack of data on breast milk rubidium (Rb) in relation to neuro-development in infants. The associations of copper (Cu), zinc (Zn) and strontium (Sr) with neuro-development in infants remain uncertain.


OBJECTIVES
We sought to evaluate the associations of breast milk Rb (primary exposure), Cu, Zn, and Sr with neuro-development in infants at age 8 months.


METHODS
The study cohort included 117 breastfed infants. Breast milk samples were collected at 42 days and 8 months postpartum. Breast milk Rb, Zn, Cu and Sr were measured by ICP-MS. Neuro-development was assessed at age 8 months. The primary outcomes were attention and working memory scores as evaluated by A-(not)B task. Other outcomes included Mental Development Index (MDI) and Psychomotor Development Index (PDI) as evaluated by Bayley Scale of Infant Development III. Generalized linear models and restricted cubic spline regression were used to assess the associations between trace elements and neuro-development indices. Bonferroni correction was conducted on all data presented.


RESULTS
A non-linear association was observed between breast milk Rb at 42 days and infant's attention at age 8 months (non-linearity P = 0.037). Positive associations were observed with infant MDI for breast milk Rb at 42 days (β = 4.46, P = 0.06) and 8 months (β = 3.79, P = 0.009) postpartum. Breast milk Zn at 42 days was positively associated with infant's attention (β = 0.31, P = 0.039). Sr at 42 days was positively correlated with attention (β = 0.18, P = 0.043) and MDI (β = 2.18, P = 0.015) at 8 months. Inverted U-shape associations were observed for breast milk Cu at 42 days with infant attention and PDI. All associations were not significant after correction for multiple tests.


CONCLUSIONS
Our data suggest that Rb, Zn, Cu, and Sr in breast milk at certain concentrations are associated with neuro-development in breastfed infants. Further studies are warranted to validate the findings.