Anthropometry before Day 46 and Growth Velocity before 6 Months of Guatemalan Breastfed Infants Are Associated with Subclinical Mastitis and Milk Cytokines, Minerals, and Trace Elements

Background: Subclinical mastitis (SCM) is an inflammatory condition of the mammary gland, but its association with human milk composition and infant growth is not well described. Objectives: We investigated whether SCM, milk cytokines, and/or estimated intakes of milk minerals and trace elements were associated with infant anthropometry or growth velocity before 6 mo. Methods: Breast milk was collected from Mam-Mayan mothers (n = 114) at both early (2-46 d) and established (4-6 mo) lactation. Concentrations of 9 elements (sodium, potassium, calcium, magnesium, copper, iron, manganese, selenium, zinc) analyzed by inductively-coupled plasma mass spectrometry were used to estimate infants' daily intakes. Concentrations of 4 cytokines were measured. Milk concentrations and infants' estimated elemental intakes and anthropometricmeasurements during early and established lactationwere compared by SCMstatus. Multiple regression was used to identify factors associated with infant growth attainment (<46 d) for infant weight-(WAZ), length-(LAZ), and head circumference-for-age (HCAZ) and weight-for-length (WLZ) z scores and with growth velocity (expressed as Delta/d) from early to established lactation. Results: SCM prevalence was higher in early (30%) than established (10%) lactation. Breast milk of SCM mothers had higher cytokine concentrations and higher magnesium in early and higher selenium concentrations in both early and established lactation (P-adj < 0.0121). At day 46, regression models showed inverse associations of SCM with WLZ and IL-1 beta with LAZ (P-adj < 0.0150). In contrast, linear growth velocity was positively associated with IL-1 beta measured in early lactation (P-adj < 0.0124), whereas cranial growth velocity was positively associated with IL-8 measured during established lactation (P-adj < 0.0124). Conclusions: Despite a high prevalence of inadequate intakes, only infants' intake of milk magnesium during early lactation was associated with linear growth velocity in breastfed infants <6 mo. Evidence shows that SCM, breast-milk cytokines, and infants' estimated intakes of select elements are independently associated with growth attainment and growth velocity during lactation.