Correlations Among Maternal and Infant Factors, Lead Exposure, and Serum Prolactin Levels During Lactation: A Cross-sectional Study in Indonesia

OBJECTIVES

Prolactin is vital for breastfeeding and milk production, and its secretion is influenced by factors related to the mother, infant, and environment. To date, no study has concurrently investigated the correlation of these factors with serum prolactin levels during lactation. Therefore, the objective of this study was to investigate the correlations among maternal and infant factors, lead exposure, and serum prolactin levels during lactation.

METHODS

A cross-sectional approach was employed in Surabaya, Indonesia, among 110 exclusively lactating mothers. The mothers' daily diets were determined using multiple 24-hour recalls, while blood lead levels were measured with inductively coupled plasma mass spectrometry. Serum prolactin levels were assessed using the electrochemiluminescence immunoassay. For bivariate analysis, we employed the Spearman correlation, Mann-Whitney, and Kruskal-Wallis tests, while for multivariate analysis, we utilized multiple linear regression.

RESULTS

The average serum prolactin level of the lactating mothers was 129.19±88.96 ng/mL. Positive correlations were found between serum prolactin levels and breastfeeding frequency (p < 0.001), protein intake (p < 0.001), and calcium intake (p = 0.011) but had negative correlation with blood lead levels (p < 0.001) and vitamin B6 intake (p = 0.003). Additionally, prolactin levels were not significantly associated with maternal age; parity; intake of calories, vitamin D, vitamin E, zinc, folic acid, magnesium, or iron; infant age; or infant sex.

CONCLUSIONS

Breastfeeding frequency had a stronger positive relationship with serum prolactin levels than protein and calcium intake. However, lead exposure was associated with reduced serum prolactin levels during lactation. Consequently, specific interventions from policymakers are necessary to manage breastfeeding in mothers exposed to lead.

The Role of Protein Intake on the Total Milk Protein in Lead-Exposed Lactating Mothers

Protein is an essential macronutrient for the growth and development of infants. Protein levels in lactating mothers are dynamic and influenced by various factors, particularly the environment and maternal characteristics. Therefore, this study aimed to evaluate the complex correlation between maternal blood lead levels (BLLs), maternal diet, and total milk protein. The Kruskal-Wallis test was used to compare total milk protein in the three groups of lead exposure, while Spearman's correlation was used to assess the correlation between maternal diet, BLLs, and total milk protein. The multivariate analysis used multiple linear regression. The results showed that the median of maternal BLLs and total milk protein were 3.3 µg/dL and 1.07 g/dL, respectively. Maternal protein intake and current BMI had a positive correlation with total milk protein, while BLLs had a negative correlation. BLLs ≥ 5 μg/dL had the most significant impact on reducing the total milk protein (p = 0.032). However, increasing maternal protein intake can effectively maintain total milk protein levels in mothers with BLLs under 5 μg/dL (p < 0.001). It is crucial to measure BLLs in lactating mothers residing in areas exposed to lead because high maternal protein intake can only maintain total milk protein levels when the BLLs are <5 μg/dL.