South Korean researchers say that encouraging pregnant women to spend more time outdoors or to increase their vitamin D supplementation may reduce the number of respiratory tract infections (RTIs) in their infants.
The team, led by Soo-Jong Hong (University of Ulsan College of Medicine, Seoul), found that low concentrations of 25-hydroxyvitamin D [25(OH)D] in cord blood were independently associated with the risk for acute nasopharyngitis in the first 6 months of life.
And, the study findings also highlight that low vitamin D status at birth is very common in the Asian population, with a combined rate of insufficiency and deficiency of 89.9%, which the authors note is much higher than that previously reported in Western populations.
“This finding may be due to ethnic differences, greater skin pigmentation, and a different geographical latitude,” they suggest.
The team studied 525 infants from whom cord blood was obtained at birth and who were followed-up until the age of 6 months.
They found that, despite the infants being otherwise healthy, only 10.1% of newborns had optimal vitamin D concentrations of 75.0 nmol/L cord blood or higher, while 55.6% and 34.3% were born with vitamin D insufficiency (25.0–74.9 nmol/L) or deficiency (<25.0 nmol/L), respectively.
Overall, 32.8% of the infants developed an RTI before the age of 6 months. The most common was acute nasopharyngitis at 28.2%, followed by otitis media and bronchiolitis, both at 5.5%.
In multivariate analysis, adjusted for multivitamin use during pregnancy, season of birth, and exposure to passive smoking during pregnancy, infants deficient in vitamin D at birth were 3.56 times more likely to develop one of these RTIs during the first 6 months of life than vitamin D-sufficient infants. Infants with vitamin D insufficiency were also 2.06 times more likely to develop an RTI in the first 6 months of life.
Cord blood concentrations did not independently associate with the risk for otitis media or bronchiolitis but vitamin D deficient and insufficient infants were 5.34 and 3.17 times, respectively, more likely to develop nasopharyngitis than vitamin D-sufficient infants during follow-up.
“This association seems to be robust, and shows a clinically and statistically significant association when controlling for potential confounders,” comment Hong et al in the Korean Journal of Pediatrics.
Noting that further studies are needed, they conclude: “The results suggest that more time spent outdoors and increased vitamin D supplementation may be necessary to increase vitamin D concentrations in pregnant women in order to protect their offspring from acute nasopharyngitis during early infancy.”
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