Many breastfed infants may not get enough vitamin D because their mothers prefer not to give babies supplement drops, a study suggests.

Pediatricians recommend that mothers exclusively breastfeed 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.

Because breast milk typically doesn't contain enough vitamin D to help infants develop healthy bones, the American Academy of Pediatrics advises nursing mothers to give their babies daily supplements of 400 IU (international units) of vitamin D. As an alternative, women can take vitamin D supplements themselves - typically 4,000 to 6,000 IU daily - to give babies enough in breast milk so that drops aren't needed.

The research team surveyed 184 breastfeeding mothers, including 44 mothers who also gave their babies formula in addition to breast milk.

Altogether, just 55 percent of the women said they gave their babies vitamin D drops and only 42 percent supplemented with the recommended 400 IU.

"Many mothers were not aware of the need for vitamin D supplementation or their physician had not recommended supplementation," said senior study author Dr. Tom Thacher, a researcher at the Mayo Clinic in Rochester, Minnesota.

"Others believed that breast milk had all the needed nutrition, and some mentioned the inconvenience of giving a supplement or their poor experience of giving a supplement to previous children," Thacher added by email.

Severe vitamin D deficiency can lead to rickets, or soft bones, seizures due to low calcium or heart failure in infants. While adults may get some vitamin D from sunlight, direct sun exposure isn't recommended for babies.

About 76 percent of mothers said they took vitamin D themselves, and most of them preferred daily supplements to longer-acting versions taken less often. Overall, nearly nine in 10 women said they would prefer to take supplements themselves rather than give drops to their babies.

Women who didn't give babies vitamin D most often cited safety concerns, the survey found.

One limitation of the study is that it included mostly white mothers, and the findings might not apply to women of other racial or ethnic groups or with a high risk of vitamin D deficiency, the authors note in the Annals of Family Medicine.

Still, the findings highlight the need to educate new parents about vitamin D and make sure breastfeeding mothers take supplements themselves or give babies drops, said Dr. Lydia Furman, a researcher at Case Western Reserve University and Rainbow Babies and Children's Hospital in Cleveland, Ohio.

"Infants can only receive adequate vitamin D if their mothers receive adequate vitamin D and thus there is adequate vitamin D in their breast milk, or if they are supplemented," Furman, who wasn't involved in the study, said by email.

Some infant formulas may contain enough vitamin D to make drops unnecessary. But babies who consume both breast milk and formula may not get enough vitamin D and still need drops or mothers who take supplements.

Many women who breastfeed incorrectly believe that this gives babies all the nutrients they need, said Dr. Carol Wagner of the Medical University of South Carolina in Charleston.

"There is an inherent belief that breast milk is the perfect food for their baby," Wagner, who wasn't involved in the study, said by email.

It's no surprise women prefer taking supplements themselves, because infant drops can be hard to remember and hard to get babies to swallow, Wagner added.

"We have found that mothers are more apt to take medications and vitamin supplements themselves than to give anything to their infants," Wagner said. "It is much easier to give a vitamin to an adult than to an infant."