Despite its health benefits and countless advocates, breastfeeding is also known as a major cause of vitamin D deficiency in infants — compared to formula milk, breastmilk has a lower vitamin D content. Researchers at Japan's Oita University used a case study involving a month-old male child who had developed hypocalcaemic seizures and dilated cardiomyopathy because of vitamin D deficiency, despite having been fed a sufficient amount of regular infant formula. He had a low birth weight (1.83kg), which saw him admitted to the neonatal ICU. There, he was fed regular formula and observed to have appropriate weight gain, and was then discharged at 24 days of age. He continued to consume regular formula after being discharged, but was not exposed to enough sunlight at home for one month. At 48 days of age, he developed an afebrile seizure and was transferred to the paediatric clinic of a regional emergency centre, where a blood test revealed he had hypocalcaemia (low blood serum levels of calcium). An intensive medical family history revealed that at 36 years old, the boy's mother had developed hyperemesis early in her pregnancy, and had then stayed in bed most of the day without sufficient food intake, which subsequently led to severe weight loss. Late in her pregnancy, she developed hypertension, and was prescribed oral methyldopa at 35 weeks of gestation. Two weeks later, she suffered jaundice, and a blood test confirmed the presence of cholestasis, with marked elevation in her levels of serum bilirubin and leucine. The doctors discontinued the methyldopa treatment after suspecting drug-induced cholestasis, after which she recovered from jaundice and the accompanying liver dysfunction. At this juncture, however, foetal growth retardation was observed, and the infant was delivered via C-section at 37 weeks and four days of gestation. His clinical and biological condition was stabilised following intensive treatment for hypocalcaemia — caused by vitamin D deficiency — but at two months old, he started to gradually exhibit signs of tachypnoea (abnormally rapid breathing). Echocardiography revealed the child had a dilated left ventricle, and he was diagnosed with congestive heart failure because of dilated cardiomyopathy. Following a period of treatment, the child’s cardiac function had recovered to nearly normal at almost six months of age. His mother's laboratory data showed improvement in cholestasis, but vitamin D deficiency persisted. In this case, the cause of vitamin D deficiency was maternal vitamin deficiency stemming from severe hyperemesis and insufficient exposure to sunlight, mainly induced by the malabsorption of fat-soluble vitamins, which was in turn caused by maternal cholestasis. The details of the case study are consistent with previous reports, which have shown that dilated cardiomyopathy can be accompanied by hypocalcaemia caused by vitamin D deficiency. The researchers wrote that in a review of 59 cases of dilated cardiomyopathy induced by hypocalcaemia, "most cases showed a reversible course with a good prognosis using treatment with calcium preparations"​. In 12 of the cases, cardiac function normalised after an average of 12.4 months. The average period before normalisation of cardiac function was eight to 12 weeks for 13 of the cases, while 14 of the cases had a two- to five-month average before normalisation. However, five deaths were also reported. The researchers concluded: "To our knowledge, detailed clinical data on the course of cardiomyopathy associated with hypocalcaemia have rarely been reported, suggesting that dilated cardiomyopathy gradually develops despite normalisation of calcium concentration in the blood with vitamin D supplementation, and that cardiac dysfunction gradually improves over several months.​ "Further studies with more patients are needed to clarify whether this clinical course was specific to this patient, or typical of cardiomyopathy induced by severe vitamin D deficiency.​ "Maternal cholestasis should be considered a risk factor for lipid-soluble vitamin deficiencies, especially vitamin D deficiency. Dilated cardiomyopathy due to vitamin D deficiency may clinically appear, even after the successful treatment of calcium metabolism."​ ​ Source: Clinical Pediatric Endocrinology​ https://doi.org/10.1297/cpe.27.187​ "Vitamin D deficiency associated with dilated cardiomyopathy in early infancy caused by maternal cholestasis"​ Authors: Tomona Omotobara-Yabe, et al.​
Breastfeeding has been linked to greater incidences of vitamin D deficiency in infants than baby formula , due to the higher incidence of vitamin D in formula . Researchers in pregnancy have called for greater monitoring of maternal health , during and after pregnancy , in order to avoid vitamin D deficiency in infants and newborns . Their recommendation follows a case study into infant onset seizures and dilated cardiomyopathy caused by vitamin D deficiency , in this case the result of maternal vitamin deficiency following hyperemesis and insufficient insulin exposure during pregnancy .