A team of researchers - led by Dr. Brent Richards, of the McGill University and the Lady Davis Institute at the Jewish General Hospital, both in Montreal, Canada - set out to determine whether or not there is a genetic background to these alleged correlations.
As the authors of the new study explain, atopy is a term that refers to a predisposition to allergic diseases including asthma and atopic dermatitis, or eczema. Atopy usually presents itself with elevated IgE levels - a type of immunoglobulin that serves to protect against parasitic infections.
The studies that correlated low vitamin D with increased IgE levels and associated disease risk were observational, the authors of the new research point out. Given that vitamin D deficiency affects over 40 percent of the population of the United States and is easy to remedy with supplements, the alleged correlation between low vitamin D and allergic disorders could be a matter of public health, the authors write.
In this context, Dr. Richards and team decided to investigate the genetic data available. The results were published in the journal PLOS Medicine.
Vitamin D supplementation will 'probably not' reduce atopic disease risk
The team examined the single nucleotide polymorphisms (SNPs) of more than 100,000 people from existing large-scale studies, such as the SUNLIGHT Consortium, the Canadian Multicentre Osteoporosis Study, and the EAGLE Eczema Consortium.
SNPs are the most common form of genetic variation found in people's DNA. The team looked at the four genetic variations that are associated with low levels of 25-hydroxyvitamin D (a marker of vitamin D insufficiency).
The researchers looked at the possible associations with adult-onset asthma and analyzed the correlations with childhood asthma separately.
The study did not find any significant differences between the incidence of asthma, atopic dermatitis, or raised IgE levels among those with the four genetic variants and those without.
However, this does not rule out the possibility of a correlation between these genetic changes and levels of the active form of vitamin D - namely, 1,25-dihydroxyvitamin D.
A further limitation of the study is that the analyses were confined to a white population of European ancestry, so the researchers do not know if the results cover non-European populations, or people with "frank vitamin D deficiency."
Dr. Despoina Manousaki, first author of the study and a Ph.D. student at the Lady Davis Institute, comments on the results:
"Our findings suggest that previous associations between low vitamin D and atopic disease could be due to spurious associations with other factors. Efforts to increase vitamin D levels will probably not result in decreased risk of adult and pediatric asthma, atopic dermatitis, or elevated IgE levels."
Dr. Richards also weighs in on the results, saying, "Our previous findings suggest that low vitamin D levels increase risk for some inflammatory diseases like multiple sclerosis, but these effects do not translate to other inflammatory diseases like asthma and atopic dermatitis."
White, European populations, and women are at a higher risk of developing multiple sclerosis.