Table 3 Summary ORs of asthma and early life blood vitamin D levels (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) | 7 | 0.98 [0.80, 1.20] | 49% | 5 | 0.79 [0.63, 0.99] | 0% | ||
 Cord blood | 2 | 1.03 [0.60, 1.79] | 0% | [23] | 1 | 2.00 [0.48, 8.31] | – | |
Period of outcome assessment | ||||||||
 At an end point (e.g. at age 1y) | 6 | 0.94 [0.75, 1.17] | 39% | 3 | 0.81 [0.64, 1.02] | 20% | ||
 Up to an end point (e.g. by age 1y) | 3 | 1.12 [0.77, 1.64] | 49% | 3 | 0.83 [0.40, 1.75] | 17% | ||
Latitude | ||||||||
 Tropics or subtropics (more intense UVR) (≤40°N/S) | [31] | 1 | 0.58 [0.29, 1.15] | – | 4 | 0.87 [0.61, 1.24] | 0% | |
 Temperate (40–66.5°N/S) | 7 | 1.01 [0.82, 1.25] | 40% | 2 | 0.77 [0.57, 1.03] | 54% | ||
Region | ||||||||
 Europe | 7 | 1.01 [0.82, 1.25] | 40% | 3 | 0.81 [0.64, 1.02] | 20% | ||
 USA/Canada |  |  |  |  | [23] | 1 | 2.00 [0.48, 8.31] | – |
 Australia | [31] | 1 | 0.58 [0.29, 1.15] | – | [45] | 1 | 0.74 [0.26, 2.14] | – |
 Asia |  |  |  |  | [35] | 1 | 0.40 [0.09, 1.80] | – |
Adjusted for family history of atopy | ||||||||
 No | 3 | 1.14 [0.88, 1.48] | 67% | 3 | 0.70 [0.50, 0.96] | 25% | ||
 Yes | 5 | 0.75 [0.55, 1.03] | 0% | 3 | 0.93 [0.68, 1.28] | 0% | ||
Adjusted for seasonality | ||||||||
 No | 3 | 0.92 [0.62, 1.37] | 69% | 2 | 0.87 [0.60, 1.26] | 0% | ||
 Yes | 5 | 0.98 [0.78, 1.24] | 30% | 4 | 0.78 [0.59, 1.03] | 35% | ||
Adjusted for smoking statues | ||||||||
 No | 3 | 1.04 [0.81, 1.33] | 52% | 2 | 0.60 [0.25, 1.44] | 0% | ||
 Yes | 5 | 0.84 [0.60, 1.18] | 44% | 4 | 0.83 [0.66, 1.04] | 26% | ||
Outcome assessment | ||||||||
 Maternal report of doctor diagnosed or medication only | 3 | 1.04 [0.75, 1.45] | 49% | 3 | 0.92 [0.64, 1.32] | 0% | ||
 Maternal report of doctor diagnosed plus medication and/or wheeze symptom | 3 | 0.90 [0.69, 1.16] | 33% | 3 | 0.75 [0.57, 1.00] | 31% | ||
 Doctor diagnosed or medical review | [41] | 1 | 0.61 [0.18, 2.13] | – |  |  |  |  |
 Other definition | [20] | 1 | 5.40 [1.09, 26.65] | – |  |  |  |  |
Blood 25(OH)D measurement | ||||||||
 LC-MS/MS (gold standard) | 5 | 0.98 [0.78, 1.24] | 30% | 5 | 0.82 [0.66, 1.03] | 2% | ||
 Other method | 3 | 0.92 [0.62, 1.37] | 69% | [35] | 1 | 0.40 [0.09, 1.80] | – | |
Risk of bias | ||||||||
 Moderate | 6 | 0.98 [0.80, 1.21] | 13% | 5 | 0.82 [0.66, 1.03] | 2% | ||
 High | 2 | 1.57 [0.18, 13.80] | 84% | [35] | 1 | 0.40 [0.09, 1.80] | – | |
Overall | 8 | 0.96 [0.79, 1.18] | 43% | 6 | 0.81 [0.65, 1.01] | 0% | ||