A new study has shown that infants who are 3-months-old and have vitamin D levels lower than 25 nanomoles per liter (nmol/L) are two times more likely to have respiratory infections, when compared to children who have levels above 75 nmol/L. In this study, published in the journal Pediatrics, vitamin D levels were measured in the umbilical cord blood samples from 900 infants. The researchers examined whether these levels of vitamin D were associated with the risk of respiratory infections, wheezing, or asthma.
Some of the earlier studies had reported that infants born to mothers who have high levels of vitamin D in the blood during pregnancy have lower risk of wheezing. In the present study, Carlos Camargo, MD, DrPH, an associate professor of medicine and epidemiology at Harvard Medical School, and colleagues analyzed data from the New Zealand Asthma and Allergy Cohort Study. The average weight of the participating infants was 7 pounds and 9 ounces and all of them were born full term at 40 weeks. Mothers of these children reported about the history of asthma, wheezing, and respiratory infection from the time the children were 3-months-old until they turned 5-years-old. The vitamin source for most of the children was sunlight while few of them took vitamin supplements.
The results of the study show that:
- About 25% of the infants had low levels of vitamin D, represented by 25-hydroxyvitamin D levels below 25 nmol/L
- The average levels of 25-hydroxyvitamin D was 44 nmol/L
- Children born in winter, children of lower socioeconomic status and children who had family histories of asthma and smoking had low vitamin D levels
- Low levels of vitamin D in the infants were found to be associated with wheezing and respiratory infection, but the levels were not associated with being diagnosed with asthma.
Dairy products like milk and cheese are good sources of vitamin D. This vitamin is important in the development of strong bones and immune system in children. Vitamin D is also produced by exposure to sunlight.
One of the major health issues among children is acute respiratory infection, especially bronchiolitis, say researchers. Bronchiolitis is the leading cause of hospitalization in infants and researchers are trying to evaluate whether vitamin D supplementation can be of help to control the same. “The present study has shown that there is an association between low levels of vitamin D and wheezing, a symptom of respiratory infections," says Camargo. Respiratory infections may often lead to asthma exacerbations too and vitamin D supplementation may be of help to prevent those events. This is particularly useful during fall and winter, when the levels of vitamin D drop normally. Researchers are hoping to confirm the results through a randomized clinical trial, which will be starting next year.