People with low levels of vitamin D appear more susceptible to upper respiratory tract infections (Zhang et al, PLOS One, Dec. 9, 2016) and even pneumonia (Haugen et al, Pediatric Research, online July 5, 2017). The research on supplementation has been inconclusive, however. Will extra vitamin D help protect children from colds?
Testing Extra Vitamin D against Respiratory Tract Infections:
A Canadian study published in JAMA compared high-dose vitamin D supplements to standard supplementation during the winter. Approximately 700 children took either 400 IUs of liquid vitamin D3 or 2000 IUs of vitamin D3. The investigators assigned them randomly so that neither they nor the parents knew which children got which dose.
Did Extra Vitamin D Make a Difference?
The two groups finished the study with a significant difference in vitamin D blood levels. However, there were no differences in the number of infections or the time before the first infection appeared. In both groups, youngsters had an average of one laboratory confirmed infection and two parent-reported infections.
According to the investigators,
“These findings do not support the routine use of high-dose vitamin D supplementation in children for the prevention of viral upper respiratory tract infections.”
Why Were Canadian Scientists Interested in Vitamin D Supplementation?
At northern latitudes sunlight is scarce and too weak to trigger vitamin D production in the winter. Consequently, Canadians may become low in the vitamin during winter months.
One study of Canadians found that one-third of them did not have adequate blood levels of vitamin D in the wintertime. Nearly half of the non-white Canadians studied had blood levels that fell short.
Vitamin D supplementation was associated with higher blood levels of the vitamin and much less seasonal variation. The investigators conclude that food choices alone are not able to maintain adequate vitamin D levels in the winter.
If you would like to learn more about vitamin D and the consequences of insufficient vitamin D, you may be interested in our Guide to Vitamin D Deficiency. This downloadable pdf describes how to avoid overdosing on extra vitamin D.