Background: Recent studies suggested low serum folate and impaired folate metabolism as potential risk factors for development of asthma and atopic disease, but the results are inconsistent. The aim of this study was to investigate the relations of markers of folate and vitamin B₁₂ (B₁₂) deficiency with different phenotypes of asthma and atopy.

Methods: A random sample of 6784 persons from a general population aged 30-60 years participated in a health examination in 1999-2001, and 4516 (66.6%) of those also participated in a follow-up examination 5 years later. The examinations included spirometry, measurements of serum folate and B₁₂, specific IgE to inhalant allergens, total IgE, and genotyping of the MTHFR-C677T polymorphism – a genetic marker of impaired folate metabolism. Information about dietary intake of folate and B₁₂, asthma diagnosis, and airway symptoms was obtained by questionnaires.

Results: Low serum folate levels and the TT genotype of the MTHFR-C677T polymorphism were associated with increased prevalence of self-reported doctor-diagnosed asthma [odds ratio (OR) 1.37, 95% confidence interval (CI) 1.05-1.79 and OR 1.52; 95% CI 1.12-2.06, respectively] and attacks of shortness of breath (OR 1.43, 95% CI 1.14-1.79 and OR 1.47; 95% CI: 1.14-1.91, respectively). We found no significant associations with lung function or atopic outcomes. Serum levels of B₁₂ and dietary intake of folate and B₁₂ were not associated with asthma or atopy.

Conclusions: We found that two objective markers of folate deficiency were associated with self-reported doctor-diagnosed asthma and attacks of shortness of breath, but not with lung function or atopy.

Thuesen BH, Husemoen LL, Ovesen L, Jørgensen T, Fenger M, Gilderson G, Linneberg A. Atopy, asthma, and lung function in relation to folate and vitamin B(12) in adults. Allergy. 2010 Nov;65(11):1446-54. doi: 10.1111/j.1398-9995.2010.02378.x. PMID: 20456312.