Research shows that vitamin D supplementation and cow's milk intake have the greatest influence on 25-hydroxyvitamin D levels in healthy children aged 1-5 years.
The team found that skin color and sun exposure did not significantly impact 25-hydroxyvitamin D levels in this cohort, but they concede that this could be at least partly "a consequence of current cultural practice of sun avoidance of young children."
Jonathon Maguire (University of Toronto, Ontario, Canada) and colleagues enrolled 1898 healthy children who were attending a routine medical checkup between December 2008 and June 2011 to take part in their study. The mean 25-hydroxyvitamin D level of the children was 35 ng/mL, which is within the normal range, and only 6% had levels below 20 ng/mL, indicating low or deficient levels.
As reported in JAMA Pediatrics, Maguire and colleagues found that taking a daily vitamin D supplement was associated with a significant 3.4 ng/mL increase in blood levels of 25-hydroxyvitamin D compared with no supplementation, after adjusting for various confounding factors including daily outdoor play time, skin pigmentation, and season.
Similarly, drinking cow's milk on a regular basis also led to significant increases in the children's 25-hydroxyvitamin D levels, amounting to 1.6 ng/mL per 250 mL cup of milk consumed after adjustment for confounders.
In addition, summer season and light skin pigmentation increased 25-hydroxyvitamin D level by a significant 1.6 and 2.7 ng/mL, respectively.
"Early childhood is a critical stage in human development, so achieving and maintaining optimal vitamin D levels in early childhood may be important to health outcomes in later childhood and adulthood," commented Maguire in a press statement.
"When it comes to maintaining sufficient vitamin D stores in young children, the story is about dietary intake of vitamin D through vitamin D supplementation and cow's milk," he said, adding that it was encouraging to find that 57% of the children in the study were already taking a regular vitamin D supplement.
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