Infants may get enough vitamin D from breast milk if their mothers take high-dose vitamin D supplements, a U.S. study suggests, offering a potential alternative to the vitamin drops parents are currently advised to give nursing babies.

Pediatricians recommend that mothers exclusively breast-feed infants until at least six months of age because it can reduce babies' risk of ear and respiratory infections, sudden infant death syndrome, allergies, childhood obesity and diabetes.

But because breast milk typically doesn't contain enough vitamin D to help infants develop healthy bones, the American Academy of Pediatrics also advises nursing mothers to give their babies daily supplements of 400 IU (international units) of vitamin D.

As an alternative to giving infants daily vitamin D drops, researchers gave mothers different doses of the supplement ranging from 400 to 6,400 IU daily. When women took the highest dose, their breast-fed babies received vitamin D levels in breast milk that were similar to the amount provided by the infant drops.

"By supplementing the mother, the baby would no longer need to be supplemented," study co-author Dr. Carol Wagner, a pediatrics researcher at the Medical University of South Carolina in Charleston, said by email. "This would be a complete paradigm shift in clinical recommendations."

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The study, published today in Pediatrics, followed 334 mother-infant pairs over six months. Researchers monitored vitamin D levels with blood and urine tests.

One limitation of the study is that over time, many of the mothers either stopped breast-feeding entirely or started offering babies some formula or solid foods, the researchers acknowledge. They also didn't test the levels of vitamin D in breast milk, relying instead on tests of vitamin D levels for the babies.

Vitamin D helps the body use calcium, and calcium in turn helps support bone health.

For most women, including nursing mothers, the recommended daily intake of vitamin D is 600 IU, though this goes up to 800 IU after age 70, according to the U.S. National Institutes of Health.

While the current study does suggest women may be able to take vitamin D supplements themselves instead of giving drops to their infants, a single study may not be enough to warrant a change in practice, said Dr. Richard So, a pediatrician at Cleveland Clinic Children's, in email to Reuters Health.

"Vitamin D is not harmless," said So, who wasn't involved in the study.

Too much vitamin D can result in a buildup of calcium in the blood that can cause poor appetite, nausea and vomiting, weakness, frequent urination and kidney problems. But serious side effects haven't been reported to U.S. drug regulators for the doses mothers took in the study, the researchers report.

Women who take supplements may increase the number of infants who receive adequate supplies of vitamin D, since only about one in five breast-fed babies receive the recommended daily drops, Dr. Lydia Furman notes in an editorial.

"For the infant, there is not a benefit or risk to receiving vitamin D through milk instead of via vitamin D drops," Furman, a pediatrician at UH Rainbow Babies & Children's Hospital in Cleveland and Case Western Reserve University, said by email. "Certainly the vitamin drops are not very delicious and sometimes make the baby gag - this is the main benefit I can think of for receiving the vitamin D via mom's breast milk."