Kids May Need Vitamin D Supplements Throughout Breastfeeding

Veronica Hackethal, MD

February 18, 2016

Breastfed children who do not receive vitamin D supplements are at risk for vitamin D deficiency, especially if breastfeeding extends beyond 1 year, according to a study published online on February 18 in the American Journal of Public Health.

The study is the first to look at the links between total time spent breastfeeding and vitamin D levels, according to researchers. It included the period beyond the first year of life, as well as children introduced to solid foods combined with breastfeeding.

"The longer the child breastfeeds beyond a year of age, the lower the vitamin D levels go. That decline is entirely preventable with vitamin D supplementation. Children who are receiving vitamin D supplementation and breastfed over a year of age didn't have that decline in levels," said senior author Jonathon Maguire, MD, pediatrician and researcher at St Michael's Hospital, Toronto, Ontario.

The findings suggest that "current recommendations about vitamin D supplementation should continue through whatever duration of breastfeeding," he added.

The Canadian Paediatric Society recommends supplementing breastfed children with 400 IU per day of vitamin D during the first year. The American Academy of Pediatrics (AAP) also recommends supplementing breastfed children with 400 IU of vitamin D, even if they are also receiving formula.

But many parents are breastfeeding beyond 1 year. For example, 20% to 30% of mothers in this study breastfed longer than 1 year, Dr Maguire pointed out.

The World Health Organization (WHO) recommends breastfeeding until 2 years of age or longer as desired by both mother and child, but the WHO guidelines do not say anything about vitamin D supplementation. Breastfeeding for that long can pose challenges, especially concerning vitamin D, which is not transferred well into breast milk.

"There's nothing wrong with breastfeeding, it's an incredible nutrient," he emphasized, "The issue is about living in northern parts of the world where moms just don't have that much vitamin D themselves."

The cross-sectional study involved 2508 healthy urban children aged 1 to 5 years who were receiving care at a participating TARGet Kids! doctor's office between September 2011 and August 2013. TARGet Kids! is a primary-care research network at the University of Toronto.

Researchers measured serum vitamin D (25-hydroxy vitamin D [25-OHD]) with a cutoff for low levels of <20 ng/mL, which indicates deficiency according to the Institute of Medicine. They determined total duration of breastfeeding and vitamin D supplementation from parental responses to standardized surveys.

Included children had a median age of 24.5 months and a median total duration of breastfeeding of 10.5 months. Of them, 5% had 25-OHD levels below 20 ng/mL, and 53% received vitamin D supplementation.

For each monthly increase in total duration of breastfeeding, vitamin D levels dropped by a mean 0.12 ng/mL among children who did not receive vitamin D supplements, compared with those who were supplemented. That translated into a 6% increase in the odds of having low vitamin D levels for each monthly increase in total time spent breastfeeding among unsupplemented children (odds ratio, 1.06; 95% CI 1.03–1.10).

After adjustment for age, BMI, total daily cow's milk intake, skin type, season, household income, and total time spent outdoors, children without vitamin D supplementation had a 16% chance of having low vitamin D levels by 2 years of age. That rose to 29% by 3 years.

There was no significant relationship between total duration of breastfeeding and vitamin D levels in children who received vitamin D supplementation.

As the authors note, limitations of the study included the use of parent-completed questionnaires and its cross-sectional nature, which could not look at time or seasonal trends. In addition, the study could not account for certain potential confounders like maternal vitamin D stores and supplementation and sources of vitamin D in the child's diet other than cow's milk. Because the study took place in Toronto, the results may not necessarily apply to regions with different levels of ultraviolet radiation.

The authors report no relevant financial relationships.

Am J Public Health. Published online February 18, 2016. Abstract

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