Fewer than a third of U.S. infants have vitamin D levels consistent with current guidelines, with breastfed infants less likely to have adequate levels than formula-fed infants, according to results of a study.

Baby drinking formula from a bottle. patrisyu/Thinkstock

The American Association of Pediatrics has recommended since 2008 that breastfeeding babies under 1 year of age receive 400 IU of vitamin D supplementation daily, usually in the form of drops, to prevent rickets. For formula-fed infants, the AAP recommends that infants be fed one liter of formula daily, as formulas must contain 400 IU of vitamin D per liter.

A study looking at caregiver-reported dietary data through 2012 suggested that the guideline was having little impact, with only 27% of U.S. infants considered to be getting adequate vitamin D. The same researchers have now updated those findings with data through 2016 to report virtually no improvement over time. For their research, published in Pediatrics, Alan E. Simon, MD, of the National Institutes of Health in Rockville, Md., and Katherine A. Ahrens, PhD, of the University of Southern Maine in Portland, analyzed data for 1,435 infants aged 0-11 months. All data were recorded during 2009-2016 as part of the ongoing National Health and Nutrition Examination Survey (NHANES).

Overall, 27% of infants in the study were considered likely to meet the guidelines. Among nonbreastfeeding infants, 31% were deemed to have adequate levels, compared with 21% of breastfeeding infants (P less than .01).

Parents’ income and education affected infants’ likelihood of meeting guidelines. Breastfeeding infants in families with incomes above 400% of the federal poverty level were twice as likely to meet guidelines (31% vs. 14%-16% for lower income brackets, P less than .05). Babies from families whose head of household had a college degree had a 26% likelihood of having enough vitamin D, compared with less than 11% of those in whose parents had less than a high school education (P less than .05). Babies from families with private insurance also had a better chance of meeting guidelines, compared with those with public insurance (24% vs. 13%; P less than .05).

Ethnicity was seen as affecting vitamin D intake only insofar as some groups had more formula use than breastfeeding. The only ethnic or racial subgroup in the study that saw more than 40% of infants likely to meet guidelines was nonbreastfeeding infants of Asian, American Indian, Native Hawaiian or Pacific Islander, or multiracial parentage, with 46% considered to have adequate vitamin D levels. This group makes up 6% of the infant population in the United States.

“Reasons for low rates of meeting guidelines in the United States and little improvement over time are not fully known,” Dr. Simon and Dr. Ahrens wrote in their analysis. “One factor may be that the impact of low vitamin D in infancy is not highly visible to physicians because rickets is an uncommon diagnosis in the United States.” They noted that recent studies from Canada, where public health officials have done more to promote supplementation, have shown rates of adequate vitamin D in breastfeeding babies to be as high as 90%.

The researchers listed among limitations of their study the fact that the data source, NHANES, captured nutrition information only for the previous 24 hours; that it relied on parental report, and did not confirm serum levels of vitamin D; and that it was possible that cow’s milk – which is not recommended before age 1 but frequently given to older infants anyway – could be a hidden source of vitamin D that was not taken into consideration.

In an editorial comment, Jaspreet Loyal, MD, and Annette Cameron, MD, of Yale University in New Haven, Conn., faulted “a combination of inconsistent prescribing by clinicians and poor adherence to the use of a supplement by parents of infants … further complicated by a lack of awareness of the consequences of vitamin D deficiency in infants among the public” for the low adherence to guidelines in the United States, compared with other countries.

Also, the editorialists noted, the dropper used to administer liquid supplements has been associated with “inconsistent precision” and concerns about infants gagging on the liquid. More research is needed to better understand “prescribing patterns, barriers to adherence by parents of infants, and alternate strategies for vitamin D supplementation to inform novel public health programs in the United States,” they wrote.

The National Institutes of Health funded the study, and Dr. Ahrens is supported by a faculty development grant from the Maine Economic Improvement Fund. The researchers declared no conflicts of interest. Dr. Loyal and Dr. Cameron disclosed no funding and no relevant financial disclosures.

SOURCE: Simon AE and Ahrens KA. Pediatrics 2020 May. doi: 10.1542/peds.2019-3574; Loyal J and Cameron A. Pediatrics. 2020 May. doi: 10.1542/peds.2020-0504.