We explored intriguing research on the nutrient's immunity-related roles in “Vitamin D May Explain the Flu… and Fight it, Too.”
Affirming those indications, a 2010 study in Japanese children and teens found that while taking 1200 IUs of vitamin D daily had no effect on rates of influenza type B, the regimen reduced the kids' risk of another major kind (influenza A)... see “Vitamin D Cuts Flu Rate in First Clinical Trial.”
According to Carlos Camargo, M.D., DrPH, who led the study, “Acute respiratory infections are a major health problem in children. For example, bronchiolitis—a viral illness that affects small airway passages in the lungs—is the leading cause of hospitalization in U.S. infants.”
Vitamin D is produced by the body in response to sunlight, and achieving adequate levels in winter can be challenging, especially in regions with significant seasonal variation in sunlight.
But many American children are deficient in the hormone-like nutrient, whose best sources are sunlight, supplements, and fatty seafood (Mansbach JM et al. 2009).
Previous studies by Camargo's team found that the children of women who took vitamin D pills during pregnancy were less likely to develop wheezing during childhood.
And as Dr. Camargo said in a press release, “Our data suggest that the association between vitamin D and wheezing, which can be a symptom of many respiratory diseases and not just asthma, is largely due to respiratory infections” (MGH 2010).
The MGH team's new study examined the relationship between newborns' blood levels of vitamin D and their risk of respiratory infection, wheezing, and asthma through age five.
Infants highest in vitamin D had the fewest respiratory infections
The Boston-based researchers analyzed data from the New Zealand Asthma and Allergy Cohort Study (Camargo CA Jr et al. 2010).
Midwives or study nurses gathered a range of measures, including samples of umbilical cord blood from newborns whose mothers enrolled them in the study.
The mothers answered questionnaires… which, among other things, asked about respiratory and other infectious diseases, the incidence of wheezing, and any diagnosis of asthma the children received from birth through age five.
The cord blood samples from 922 newborns—which provide an accurate measure of blood chemistry at birth—were analyzed for vitamin D levels.
More than 20 percent of them had vitamin D levels less than 25 nmol/L, which is considered very low.
The average level in the newborns was just 44 nmol/L… many researchers believe that the target level for most people should be as high as 100 nmol/L.
Vitamin D levels were lowest among children born in winter, from families of lower socioeconomic status, and with familial histories of asthma or smoking.
Dr. Camargo noted that very few children in this study took supplements before age five; their post-natal vitamin D status was primarily a function of the amount of sun exposure they got.
By the age of 3 months, infants with vitamin D levels below 25 nmol/L were twice as likely to have developed respiratory infections as those with levels of 75 nmol/L or higher.
(They arrived at this number after adjusting for more than 12 potential “confounders”—that is, other factors affecting the risk for lung infections—which did not materially change the results.)
Survey results covering the first five years of the infants' lives showed that the lower their neonatal vitamin D level, the higher their risk of wheezing.
But no significant association was seen between the infants' vitamin D levels and receiving a diagnosis of asthma by the age of five.
Some previous studies had suggested that unusually high levels of vitamin D might increase the risk for allergies, but no such association was seen among study participants with the highest levels.
Sadly, as Dr. Camargo and his colleagues wrote in a 2009 paper, “millions of [American] children may have suboptimal levels of [vitamin D], especially non-Hispanic black and Hispanic children” (Mansbach JM et al. 2009).
Dr. Camargo stressed that the study results do not mean that vitamin D levels are unimportant for people with asthma:
“There's a likely difference here between what causes asthma and what causes existing asthma to get worse.
“Since respiratory infections are the most common cause of asthma exacerbations, vitamin D supplements may help to prevent those events, particularly during the fall and winter when vitamin D levels decline and exacerbations are more common.
“That idea needs to be tested in a randomized clinical trial, which we hope to do next year” (MGH 2010).
Stay tuned… we'll let you know how that trial turns out.
Camargo CA Jr, Ingham T, Wickens K, Thadhani R, Silvers KM, Epton MJ, Town GI, Pattemore PK, Espinola JA, Crane J; the New Zealand Asthma and Allergy Cohort Study Group. Cord-Blood 25-Hydroxyvitamin D Levels and Risk of Respiratory Infection, Wheezing, and Asthma. Pediatrics. 2011 Jan;127(1):e180-e187. Epub 2010 Dec 27.
Mansbach JM, Ginde AA, Camargo CA Jr. Serum 25-hydroxyvitamin D levels among US children aged 1 to 11 years: do children need more vitamin D? Pediatrics. 2009 Nov;124(5):1404-10. Erratum in: Pediatrics. 2009 Dec;124(6):1709.
Massachusetts General Hospital (MGH). Newborns with low vitamin D levels at increased risk for respiratory infections. December 27,2010. Accessed at http://www.eurekalert.org/pub_releases/2010-12/mgh-nwl122210.php