Genetic study suggests vitamin D is not linked to asthma or dermatitis

Genetic study suggests vitamin D is not linked to asthma or dermatitis

Supplementation with vitamin D ‘is unlikely’ to reduce the risk of asthma, atopic dermatitis, or allergies, a new genetic study has found.

The research, published in PLOS Medicine, researchers looked at genetic and health data from more than 100,000 people who took part in previous large-scale studies in a bid see whether genetic alterations associated with vitamin D levels predispose people to asthma, dermatitis, or high IgE levels.

A number of previous studies have suggested that lowered vitamin D levels are linked to increased rates of asthma, atopic dermatitis – itchy inflammation of the skin – and higher levels of immune molecules – known as IgE – that are linked to allergy.

Led by Dr Despoina Manousaki at the Lady Davis Institute in Canada, the team reported no statistically significant difference between rates of asthma (including childhood-onset asthma), atopic dermatitis, or IgE levels in people with or without any of the four genetic changes associated with lower levels of 25-hydroxyvitamin D.

"Our findings suggest that previous associations between low vitamin D and atopic disease could be due to spurious associations with other factors," said Manousaki. "Efforts to increase vitamin D levels will probably not result in decreased risk of adult and paediatric asthma, atopic dermatitis, or elevated IgE levels."

However, the new findings contrast with work previously done by the same group – which used similar methods to provide evidence supporting a role for vitamin D in the risk of multiple sclerosis.

"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", noted senior author Dr Brent Richards of McGill University, Canada.

Genetic study

Manousaki and colleagues tested whether genetically lowered vitamin D levels were associated with risk of asthma, atopic dermatitis, or elevated serum IgE levels, using Mendelian randomization (MR) methodology.

The team used data from 33,996 individuals in the UK Biobank resource and the SUNLIGHT, GABRIEL and EAGLE eczema consortia.

Using this data, the team filtered for four genetic trails known as single-nucleotide polymorphisms (SNPs) which are strongly associated with 25-hydroxyvitamin D (25OHD) levels.

“We conducted MR studies to estimate the effect of lowered 25OHD on the risk of asthma (n = 146,761), childhood onset asthma (n = 15,008), atopic dermatitis (n = 40,835), and elevated IgE level (n = 12,853) and tested MR assumptions in sensitivity analyses,” wrote the team.

“None of the four 25OHD-lowering alleles were associated with asthma, atopic dermatitis, or elevated IgE levels,” they said.

As a result, the team concluded that there is no evidence that genetically determined reductions in vitamin D levels leads to an increased risk of asthma, atopic dermatitis, or elevated total serum IgE, “suggesting that efforts to increase vitamin D are unlikely to reduce risks of atopic disease.”

The authors added that previous epidemiological associations between vitamin D and atopic diseases ‘could be due to confounding’ – with factors such as obesity and physical inactivity possible.

Source: PLOS Medicine
Published online ahead of print, doi: 10.1371/journal.pmed.1002294
“Vitamin D levels and susceptibility to asthma, elevated immunoglobulin E levels, and atopic dermatitis: A Mendelian randomization study”
Authors: Despoina Manousaki, et al

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