Manchester study confirms babies can safely continue breastfeeding despite high calcium levels

A new study led by researchers at Royal Manchester Children’s Hospital (RMCH), part of Manchester University NHS Foundation Trust (MFT) has found that some exclusively breastfed babies develop naturally high calcium levels in their blood, but importantly, the condition is harmless, temporary, and does not require stopping breastfeeding or switching to low calcium formula milk.

Researchers analysed the medical records of 25 babies, aged under six-months-old who were admitted to hospital for common issues such as jaundice or feeding concerns, and were incidentally noted to have increased calcium levels (known as hypercalcaemia).

Every baby in the study was asymptomatic, showing none of the typical side effects of hypercalcaemia such as vomiting, constipation, lethargy, or poor feeding, and they all had a suppressed parathyroid hormone (PTH), which is responsible for regulating calcium levels.

The team discovered that although the babies had high calcium in their blood and in some cases, high calcium in their urine, none of the babies showed any kidney damage. All babies went on to have a kidney ultrasound scan, and every scan was normal – with no sign of calcium building up in the kidneys, which is the main concern with hypercalcaemia.

All infants continued exclusively breastfeeding, and their calcium levels were monitored regularly until they settled naturally and returned to normal levels.

The study showed most babies reached their highest calcium levels in the first three weeks of life, and the elevated levels typically resolved by around two months.

Dr Amish Chinoy, Consultant in Paediatric Endocrinology and Metabolic Bone Disorders at RMCH, who led this work, said: “This research is the first of its kind and provides reassurance for both parents and healthcare professionals that a high calcium result in an otherwise healthy, fully breastfed baby is usually nothing to fear, and breastfeeding remains safe and should continue.

“This is likely part of normal development rather than an illness but if any parents are concerned about their baby, please seek further medical attention.”

The researchers have called this “breast milk–associated physiological hypercalcaemia” to highlight that this is a normal, self‑resolving condition. Research results suggest that the rise in calcium is a temporary and harmless effect of exclusive breastfeeding for some infants.

This condition is very different to rare genetic conditions that can also cause high calcium with low PTH levels, such as idiopathic infantile hypercalcaemia or Williams syndrome, which can lead to serious problems if left untreated.

Dr Chinoy added: “The next step in this research is to carry out simple hormone‑related blood tests in babies, to help us better understand what might be contributing to this and why it happens.”

This research was published in BMJ Paediatrics Open Journal in May 2026.