Breast milk–associated physiological hypercalcaemia: an observational study of clinical, biochemical and radiological outcomes

INTRODUCTION: Asymptomatic physiological hypercalcaemia in exclusively breastfed infants is recognised but has not been systematically characterised when breastfeeding is continued. OBJECTIVE: To evaluate the clinical, biochemical and radiological outcomes of breast milk-associated physiological hypercalcaemia. METHODS: A multi-centre retrospective study over 5 years included infants with hypercalcaemia (serum corrected calcium (cCa) ≥2.8 mmol/L) who were exclusively breastfed and had no other identifiable causes of hypercalcaemia. Clinical, biochemical and radiological data were analysed. RESULTS: Twenty-five infants (15 males, 10 females) were studied. The mean peak cCa was 3.08 mmol/L (SD 0.17; normal 2.2-2.8 mmol/L). All infants were asymptomatic and continued exclusive breastfeeding without interventions such as intravenous fluids, diuretics or bisphosphonates. Mean serum parathyroid hormone (PTH) was suppressed at 1.04 pmol/L (SD 0.9; reference 2.0-9.4 pmol/L). Renal ultrasound examinations performed in all infants showed no nephrocalcinosis. Hypercalcaemia resolved spontaneously over a median of 64 (range, 9-329) days, and the median duration of exclusive breastfeeding was 150 (range, 8-540) days. CONCLUSION: Breast milk-associated physiological hypercalcaemia is a benign, PTH-independent condition without clinical symptoms or nephrocalcinosis. Infants can safely continue exclusive breastfeeding, preserving its well-established benefits, without switching to low calcium formulas. Further research is needed to elucidate the underlying mechanisms.