Vitamin D supplementation cuts childhood colds and flu in half

Tuesday, August 28, 2012. A report published online on August 20, 2012 in the journal Pediatrics reveals a dramatic decrease in the incidence of wintertime acute respiratory tract infections (ARIs) in children supplemented with vitamin D. Although observational studies have associated a lower risk of the infections with higher vitamin D levels, the investigation is one of the first randomized, double-blinded trials to study the effects of vitamin D supplementation on childhood ARI.

The trial included 247 children residing in Mongolia, which receives limited winter sunlight. Participants had a median serum 25-hydroxyvitamin D concentration of 7 nanograms per milliliter (ng/mL) at the beginning of the study (a deficient level associated with reduced sunlight exposure). One hundred forty-three children received milk fortified with 300 international units (IU) vitamin D per day and 104 subjects received unfortified milk for seven weeks beginning in late January.

At the trial's conclusion, vitamin D levels increased to a median of 19 ng/mL among those who received vitamin D fortified milk while remaining the same among the control group. Parents of subjects who received vitamin D reported 48 percent fewer respiratory infections in their children over the course of the study compared with those whose children did not receive the vitamin. Adjustment for age and other factors resulted in a similar, 50 percent lower risk in the supplemented group.

"Our randomized controlled trial shows that vitamin D has important effects on infection risk," stated first author and Harvard Medical School professor of Medicine Carlos Camargo, MD. "In almost 250 children with low blood levels of vitamin D during winter, we found that taking a daily vitamin D supplement cut in half the risk of a respiratory infection."

"Our study design provides strong evidence that the association between low vitamin D and respiratory infections is causal and that treating low vitamin D levels in children with an inexpensive and safe supplement will prevent some respiratory infections," he added. "The large benefit was undoubtedly related to the low baseline vitamin D levels of these children, so I would not expect the supplement to provide similar benefit in children who start with healthy levels of vitamin D. The key question for future research is at what initial vitamin D level would children no longer receive benefit from winter supplementation?"

"At the time the trial was designed, the Institute of Medicine recommended 200 IU daily for all individuals from birth to age 50 years," the authors write. "The 2011 Institute of Medicine report has since increased the recommendation to 400 IU daily for children. Although this higher dose is certainly an improvement, we suspect that even 400 IU daily will fall short for many children with vitamin D deficiency. Other groups, such as the Canadian Paediatric Society, recommend 1000 IU daily for children, and we believe that this higher dose is more likely to achieve adequate 25-hydroxyvitamin D levels for almost all children without pushing them to a potentially toxic level."