Breastfed babies living in northern latitudes often lack healthy levels of vitamin D, and may even be severely deficient, results of a new study suggest.

“In northern latitudes, such as that in Iowa (41 degrees North), sunshine is too diminished in the winter for the infants to generate enough vitamin D on their own,” lead author Dr. Ekhard E. Ziegler told Reuters Health.

Ziegler, from the University of Iowa in Iowa City, and his team analyzed blood samples from 84 infants when they were about 9 months old. Forty-nine received vitamin D, either from formula or supplements, while 35 were breastfed and received no supplements.

Eight breastfed infants were considered to be deficient, defined as having blood levels of the active metabolite of vitamin D - 25-hydroxyvitamin D - (25-OHD) of less than 11 nanograms per milliliter. Two of these infants were considered to be severely deficient, with levels below 5 nanograms per milliliter.

More infants were vitamin D deficient during winter (37 percent) than during summer (2 percent), and more dark-skinned than light-skinned infants were deficient (43 percent versus 6 percent).

According to their report in the journal Pediatrics, the investigators conducted another analysis of breastfed babies from ages 4 to 15 months. The results suggest that the deficiency is less prevalent as babies get older.

How did this high prevalence of vitamin D deficiency come about in a developed country? According to Ziegler, “at the beginning of the last century, it was standard practice to give infants a teaspoon of cod liver oil, which averages about 440 IU of 25-OHD per day.” When the use of baby formula became popular, enough vitamin D was added to the formula to prevent deficiency.

“Then since the 1970s,” he explained, “women returned to breast feeding, but they never resumed the practice of giving their babies any dietary supplements.”

Currently the American Academy of Pediatrics recommends vitamin D supplements of 200 IU per day for breastfed infants. “But they also include the proviso that supplements may not be required if there is adequate exposure to sunshine,” Ziegler added, “which they fail to define.”

So his advice is to give vitamin D supplements to breastfed infants living in northern latitudes, “at least in winter, which lasts from November to May here in Iowa.”

SOURCE: Pediatrics, August 2006.