Table 4 Summary ORs of asthma and early life vitamin D intake (highest versus lowest category) in cohort studies, according to selected subgroups
From: Early life vitamin D status and asthma and wheeze: a systematic review and meta-analysis
Age at outcome assessment >5y | Age at outcome assessment ≤5y | |||||||
|---|---|---|---|---|---|---|---|---|
Subgroup | Studies (Ref. no.) | No. of studies | OR (95% CI) | I2 | Studies (Ref. no.) | No. of studies | OR (95% CI) | I2 |
Window of exposure assessment | ||||||||
 During pregnancy (mother) | 2 | 1.21 [0.90, 1.62] | 64% | 4 | 0.89 [0.77, 1.04] | 68% | ||
 During infancy | [52] | 1 | 0.74 [0.56, 0.96] | – | 2 | 0.95 [0.85, 1.06] | 27% | |
Period of outcome assessment | ||||||||
 At an end point (e.g. at age 1y) | 3 | 0.90 [0.56, 1.45] | 77% | [54] | 1 | 0.60 [0.27, 1.31] | – | |
 Up to an end point (e.g. by age 1y) | [50] | 1 | 0.60 [0.32, 1.11] | – | 5 | 0.94 [0.86, 1.02] | 60% | |
Latitude | ||||||||
 Tropics or subtropics (more intense UVR) (≤40°N/S) | – | – | – | – | [54] | 1 | 0.60 [0.27, 1.31] | – |
 Temperate (40–66.5°N/S) | 3 | 0.90 [0.56, 1.45] | 77% | 5 | 0.94 [0.86, 1.02] | 60% | ||
Region | ||||||||
 Europe | 3 | 0.90 [0.56, 1.45] | 77% | 4 | 0.96 [0.88, 1.05] | 47% | ||
 USA/Canada |  |  |  |  | [55] | 1 | 0.65 [0.46, 0.93] | – |
 Asia |  |  |  |  | [54] | 1 | 0.60 [0.27, 1.31] | – |
Adjusted for family history of atopy | ||||||||
 No | [57] | 1 | 1.33 [0.97, 1.82] | – | [55] | 1 | 0.65 [0.46, 0.93] | – |
 Yes | 2 | 0.73 [0.56, 0.94] | 0% | 5 | 0.95 [0.87, 1.04] | 43% | ||
Adjusted for seasonality | ||||||||
 No | [57] | 1 | 1.33 [0.97, 1.82] | – | 4 | 0.64 [0.48, 0.86] | 29% | |
 Yes | 2 | 0.73 [0.56, 0.94] | 0% | 2 | 0.97 [0.88, 1.06] | 0% | ||
Adjusted for smoking statues | ||||||||
 No | [57] | 1 | 1.33 [0.97, 1.82] | – | [56] | 1 | 3.16 [0.61, 16.32] | – |
 Yes | 2 | 0.73 [0.56, 0.94] | 0% | 5 | 0.93 [0.85, 1.01] | 56% | ||
Outcome assessment | ||||||||
 Maternal report of doctor diagnosed or medication only | [50] | 1 | 0.60 [0.32, 1.11] | – | 2 | 0.94 [0.85, 1.05] | 71% | |
 Maternal report of doctor diagnosed plus medication and/or wheeze symptom | 3 | 0.90 [0.56, 1.45] | 77% | 2 | 0.82 [0.55, 1.24] | 77% | ||
 Doctor diagnosed or medical review | – | – | – | – | [54] | 1 | 0.60 [0.27, 1.31] | – |
 Based on ISAAC questionnaire | – | – | – | – | [56] | 1 | 3.16 [0.61, 16.32] | – |
Risk of bias | ||||||||
 Moderate | 2 | 0.98 [0.55, 1.75] | 87% | 4 | 0.96 [0.88, 1.06] | 14% | ||
 High | [50] | 1 | 0.63 [0.28, 1.44] | – | 2 | 0.61 [0.45, 0.84] | 0% | |
Overall | 3 | 0.90 [0.56, 1.45] | 77% | 6 | 0.93 [0.85, 1.02] | 56% | ||