Table S3. The characteristics of included study (cross-section study).

Study	Study Design	Definition of outcomes	Measurement of folate/folic acid status	Main Findings	Study Limitations	Adjusted factors
Thuesen 200924	Cross-sectional study of 1,207 adults (15-77 yr) in Denmark, carried out in 1997-1998	Asthma: diagnose of allergic asthma, and self-reported allergy and asthma SPT reactivity: at least one positive SPT sIgE positivity: a positive test to at least one of the six inhalant allergens	MTHFRC677T polymorphism	No significant associations between MTHFRC677T polymorphism and asthma or allergy	Lack of data on folate levels, and potential selection bias	Sex, age, BMI, smoking, social status and alcohol intake
Matsui 200925	Cross-sectional study of 8,083 individuals (≥2 yr) in USA, collected data from the 2005-2006 National Health and Nutrition Examination Survey Wheeze: symptom Atopy: at least 1 positive allergen-specific IgE level	Asthma: doctor-diagnosed	Serum folate level	Higher serum folate levels were inversely associated with a lower risk of wheeze and atopy, but not with asthma	Nonassessment of the effect with different age group, and lack of data on dietary intake	Age, sex, race/ethnicity, and poverty income ratio
Woods 200326	Cross-sectional study of 1,601 adults in Australia, carried out in 1999 Atopy: a ≥3 mm wheal diameter in response to any allergen in SPT	Asthma: self-reported or doctor-diagnosed	folate consumption from foods	No consistent associations between intakes of folate and asthma, BHR, or atopy	Potential selection bias	Age, sex, body mass index, smoking status, region of birth, and family history of asthma