This isn't the first time that the topic has come up.
Since 2003, the American Academy of Pediatrics has recommended vitamin D supplementation of 200 international units (IU) per day for all infants who don't get at least 500 milliliters of vitamin D-fortified formula or milk. That includes breastfed babies, since breast milk is low in vitamin D.
Forty percent of those kids had suboptimal blood levels of vitamin D, including 12% who had vitamin D deficiency. And X-rays showed that a third of kids with vitamin D deficiency had bone demineralization, a sign of thinner bones, report Catherine M. Gordon, MD, MSc, and colleagues.
Breastfed babies were particularly likely to be low in vitamin D. Then again, only 20 babies in the study were exclusively breastfed, and only six of those infants had gotten vitamin D supplements.
"The current findings support recommendations advocating for vitamin D supplementation for all young children," Gordon's team writes.
The vitamin D thresholds used in the study are largely based on research done on adults, and it's not clear whether those benchmarks hold for children, notes the University of Washington's James Taylor, MD, in an editorial published with the study in the Archives of Pediatrics & Adolescent Medicine.