@article{Skaaby2018,
title = {Associations of genetic determinants of serum vitamin B12 and folate concentrations with hay fever and asthma: a Mendelian randomization meta-analysis.},
author = {T Skaaby and AE Taylor and RK Jacobsen and LT Møllehave and N Friedrich and BH Thuesen and DM Shabanzadeh and L Paternoster and U Völker and M Nauck and H Völzke and M Munafò and T Hansen and O Pedersen and T Jørgensen and N Grarup and A Linneberg},
url = {https://www.ncbi.nlm.nih.gov/pubmed/29249824},
year = {2018},
date = {2018-02-07},
journal = {European Journal of Clinical Nutrition},
abstract = {Studies of the effect of vitamin B12 and folate on the risk of asthma and hay fever have shown inconsistent results that may be biased by reverse causation and confounding. We used a Mendelian randomization approach to examine a potential causal effect of vitamin B12 and folate on hay fever, asthma, and selected biomarkers of allergy by using 11 vitamin B12-associated single-nucleotide polymorphisms (SNPs) and 2 folate-associated SNPs as unconfounded markers.
SUBJECTS/METHODS:

We included 162,736 participants from 9 population-based studies including the UK Biobank. Results were combined in instrumental variable and meta-analyses and effects expressed as odds ratios (ORs) or estimates with 95% confidence interval (CI).
RESULTS:
Using genetic proxies for B12 and folate, instrumental variable analyses did not show evidence for associations between serum B12 and hay fever: OR = 1.02 (95% CI: 0.98, 1.05), asthma: OR = 0.99 (95% CI: 0.95, 1.04), allergic sensitization: OR = 1.02 (95% CI: 0.74, 1.40), or change in serum IgE: 10.0% (95% CI: -9.6%, 29.6%) per 100 pg/ml B12. Similarly, there was no evidence for association between serum folate and hay fever: OR = 0.74 (95% CI: 0.45, 1.21), asthma: OR = 0.80 (95% CI: 0.43, 1.49), or allergic sensitization: OR = 1.92 (95% CI: 0.11, 33.45), but there was a statistically significant association with change in serum IgE: 2.0% (95% CI: 0.43%, 3.58%) per 0.1 ng/ml serum folate.
CONCLUSIONS:

Our results did not support the hypothesis that levels of vitamin B12 and folate are causally related to hay fever, asthma, or biomarkers of allergy, but we found evidence of a positive association between serum folate and serum total IgE.},
keywords = {17765, genetics},
pubstate = {published},
tppubtype = {article}
}

@article{Taylor22017,
title = {Estimating the causal effect of body mass index on hay fever, asthma and lung function using Mendelian randomization.},
author = {Møllehave 4 | L T T. Skaaby1 | A. E. Taylor2 3 | B. H. Thuesen1 | R. K. Jacobsen1 | N. Friedrich1 and S Hansen and Larsenaand S C U V€olker and M Nauck and H Volzke and T Hansen and O Pedersen and T Jørgensen and L Paternoster and M Munaf and N Grarup and A Linneberg},
year = {2017},
date = {2017-07-04},
journal = {Allergy},
abstract = {BACKGROUND:

Observational studies have shown that body mass index (BMI) is positively associated with asthma. However, observational data are prone to confounding and reverse causation. In Mendelian randomization, genetic variants are used as unconfounded markers of exposures to examine causal effects. We examined the causal effect of BMI on asthma, hay fever, allergic sensitization, serum total immunoglobulin E (IgE), forced expiratory volume in one-second (FEV1) and forced vital capacity (FVC).

METHODS:

We included 490 497 participants in the observational and 162 124 participants in the genetic analyses. A genetic risk score (GRS) was created using 26 BMI-associated single nucleotide polymorphisms (SNPs). Results were pooled in meta-analyses and expressed as odds ratios (ORs) or β-estimates with 95% confidence interval (CI).

RESULTS:
The GRS was significantly associated with asthma (OR=1.009; 95% CI: 1.004, 1.013), but not with hay fever (OR= 0.998; 95% CI: 0.994, 1.002) or allergic sensitization (OR=0.999; 95% CI: 0.986, 1.012) per BMI-increasing allele. The GRS was significantly associated with decrease in FEV1: β=-0.0012 (95% CI: -0.0019, -0.0006) and FVC: β=-0.0022 (95% CI: -0.0031, -0.0014) per BMI-increasing allele. Effect sizes estimated by instrumental variable analyses were OR=1.07 (95% CI: 1.03, 1.10) for asthma, a 9 ml decrease in FEV1 (95% CI: 2.0-15 mL decrease) and a 16 ml decrease in FVC (95% CI: 7.0-24 mL decrease) per 1 kg/m2 higher BMI.

CONCLUSIONS:

The results support the conclusion that increasing BMI is causally related to higher prevalence of asthma and decreased lung function, but not with hay fever or biomarkers of allergy.},
keywords = {17765, hay fever, lung function},
pubstate = {published},
tppubtype = {article}
}