Overview of the identified risk factors for adult-onset asthma, and their corresponding effect sizes
| Category | Risk factor | Number of reviews | Effect measure | Effect size (95% CI), reference |
| Air pollution and chemical exposures | Indoor formaldehyde exposure | 1 | OR | 1.81 (1.18–2.78) [21] |
| VOC exposure | 1 | NA | NA [27] | |
| Air pollution (NO2, PM10, O3) | 1 | OR | Range: 1.03–1.22 [31] | |
| Pesticide exposure | 1 | OR | Range: 0.41 (0.15–1.11)–3.67 (1.19–11.30) [46] | |
| Phthalate exposure | 1 | OR | 1.55 (1.18–2.05) [47] | |
| Domestic paint exposure | 1 | OR | 1.60 (1.00–2.50) [43] | |
| Arachidonic acid intake | 1 | NA | NA [38] | |
| Domestic cleaning products | 1 | NA | NA [49] | |
| Early life exposures | Low birth weight | 1 | OR | 1.25 (1.12–1.40) [29] |
| Early life vitamin D deficiency | 1 | OR | 0.57 (0.35–0.93) [26] | |
| High birth weight | 1 | OR | 1.26 (0.88–1.82) [45] | |
| High weight during childhood | 1 | OR | 1.32 (0.82–2.40) [45] | |
| Pre-term delivery | 1 | OR | Range: 1.86 (0.23–12.00)–1.14 (0.92–1.40) [41] | |
| Nutrition and weight status | BMI between 25 and 29.9 kg·m−2 | 1 | OR | 1.38 (1.17–1.62) [40] |
| BMI ≥30 kg·m−2 | 2 | OR | 1.92 (1.43–2.59) [40]; 2.02 (1.63–2.50) [31] | |
| BMI per kg·m−2 increase | 1 | Risk ratio | 1.05 (1.03–1.07) [42] | |
| Vitamin B12 | 1 | Risk ratio | 0.99 (0.95–1.04) [42] | |
| Iron | 1 | Risk ratio | 0.92 (0.67–1.25) [42] | |
| Folate | 1 | Risk ratio | 0.80 (0.43–1.21) [42] | |
| Linoleic acid | 1 | Risk ratio | 0.89 (0.85–0.93) [42] | |
| Alcohol intake | 1 | Risk ratio | 0.95 (0.91–0.99) [42] | |
| Zinc plasma levels | 1 | SMD | −0.26 (−0.40– −0.13) [23] | |
| Selenium plasma levels | 1 | SMD | −0.06 (−0.13–0.02) [23] | |
| Occupational exposures | Cleaning products | 2 | Risk ratio/OR | Risk ratio: 1.67 (1.11–2.50) [20]; OR range: 1.50–3.00 [48] |
| Workplace irritants | 1 | NA | NA [44] | |
| Wood dust exposure | 1 | Risk ratio | 1.53 (1.25–1.87) [34] | |
| Organic dust (wood, textile, etc.) | 1 | OR | Paper/wood: 1.62 (1.38–1.90); flour/grain: 1.48 (1.11–1.97); textile: 1.50 (1.08–2.09) [25] | |
| Persulphates (e.g. hair bleach) | 1 | NA | NA [30] | |
| Physiological, personal and socioeconomic characteristics | Younger age at menarche | 1 | OR | 1.37 (1.15–1.64) [37] |
| Age at puberty: early versus average | 1 | Risk ratio | 1.10 (1.04–1.15) [42] | |
| Age at puberty: late versus average | 1 | Risk ratio | 0.93 (0.90–0.96) [42] | |
| Smoking | 3 | Percentage/risk ratio/OR | 56% [36]; 0.97 (0.96–0.99) (risk ratio) [42]; 1.66 (1.44–1.90) (OR) [31] | |
| Second-hand smoke | 1 | OR | 1.44 (1.30–1.60) [31] | |
| Housing-related factors, e.g. mould | 1 | OR | Range: 1.43–1.73 [31] | |
| Acetaminophen use | 1 | OR | 1.63 (1.46–1.77) [24] | |
| Living in urban areas | 1 | OR | 1.89 (1.47–2.41) [32] | |
| Low SES | 1 | OR | 1.38 (1.37–1.39) [35] | |
| Female sex | 1 | Percentage | 58–75% [36] | |
| Male sex | 1 | OR | 1.30 (1.23–1.38) [31] | |
| Indoor fungi exposure | 1 | OR | 1.25 (0.99–1.58) [28] | |
| Temperature drops | 1 | OR | 1.00 (0.93–1.08) [33] | |
| Indoor furry pets | 1 | OR | 1.58 (0.99–2.54) [39] | |
| Exposure to greenness | 1 | NA | NA [22] |
95% confidence intervals are given when available. BMI: body mass index; NA: not assigned, indicates studies without a meta-analysis and without effect sizes; PM: particulate matter; SES: socioeconomic status; SMD: standardised mean difference; VOC: volatile organic compound.