Table 2.
Main findings for each study including whether there was evidence of altered maternal or fetal/neonatal thyroid function, the outcome assessed, and the directionality of associations with air pollution exposure
| Study | Evidence of altered maternal thyroid function | Evidence of altered fetal/neonatal thyroid function | Outcome assessed/directionality of association |
|---|---|---|---|
| Chamot et al. [41] | -- | Yes | ↑ Increased exposure to PM2.5 and PM10 was associated with an increase in TSH concentration |
| Ghassabian et al. [42] | Yes | -- |
↑ Increased exposure to PM2.5 was associated with increased odds of hypothyroxinemia ⦸ No statistically significant association between exposure to PM10, PM2.5-10, PM2.5absorbance, NO2, and NOx and odds of hypothyroxinemia or high TSH concentration. No statistically significant association between exposure to PM2.5 and odds of high TSH concentration |
| Gong et al. [43] | Yes | -- |
↑ Increased exposure to PM2.5 and PM10 was associated with an increase in FT4 concentration ⦸ No statistically significant association between exposure to PM2.5 and PM10 and TSH concentration |
| Harari-Kremer et al. [44] | -- | Yes |
↑ Increased exposure to NO2 and NOx was associated with increased odds of developing CHT ⦸ No statistically significant association between exposure to PM2.5 and PM10-2.5 and odds of developing CHT |
| Howe et al. [45] | -- | Yes |
↑ Increased exposure to PM2.5 and PM10 was associated with increased TT4 concentration ⦸ No statistically significant association between NO2, O3, or NOx and TT4 concentration |
| Ilias et al. [46] | Yes | -- |
↑ Increased exposure to PM2.5 was associated with increased logTSH concentration ⦸ No statistically significant association between exposure to PM10 and NO2 and TSH concentration |
| Irizar et al. [47] | -- | Yes |
↑ Increased exposure to PM2.5 was associated with increased TT4 concentration ⦸ No statistically significant association between exposure to NO2 and TT4 concentration |
| Janssen et al. [33] | No | Yes |
↓ Increased exposure to PM2.5 was associated with decreased fetal TSH, FT4, and FT4/FT3 ratio concentrations ↑ Increased exposure to PM2.5 was associated with increased fetal FT3 concentration ⦸ No statistically significant associations between exposure to PM2.5 and maternal FT4, FT3, FT4/FT3 ratio, or TSH concentrations |
| Li et al. [48] | Yes | -- |
↑ Increased exposure to PM2.5 was associated with increased FT3 concentration ↓ Increased exposure to PM2.5 was associated with decreased FT4 and FT4/FT3 ratio concentration ⦸ No statistically significant associations between exposure to PM2.5 and TSH concentration |
| Nourouzi & Chamani [49] | -- | Yes | ↑ Increased exposure to PM2.5 and CO was associated with increased TSH concentration |
| Qi et al. [50] | -- | Yes |
↑ Increased exposure to O3 and NO2 was associated with an increased risk of CHT ⦸ No statistically significant association between exposure to SO2 and CO and risk of CHT |
| Qiu et al. [51] | Yes | -- |
↑ Increased exposure to PM2.5-bound Ba was associated with increased FT4 concentration. Increased exposure to PM2.5-bound Be and Mn were associated with increased FT3 concentration. Increased exposure to PM2.5-bound As, Cr, Se, Tl, and Ba were associated with increased FT4/FT3 ratio concentration ↓ Increased exposure to CO, NO2, and PM2.5-bound Be, Pb, Mn, and Ni were associated with decreased FT4 concentration. Increased exposure to PM2.5, PM10, CO, SO2, and PM2.5-bound As, Cr, Se, and Tl were associated with decreased FT3 concentration. Increased exposure to PM2.5-bound Al, Be, Pb, Mn, and Ni were associated with decreased FT4/FT3 ratio concentration ⦸ No statistically significant associations were observed between exposure to any of the pollutants and TSH concentration |
| Shang et al. [52] | -- | Yes |
↑ Increased exposure to PM2.5 was associated with an increased risk of CHT ⦸ No statistically significant association between exposure to PM10 and risk of CHT |
| Sun et al. [53] | Yes | -- | ↑ Increased exposure to PM2.5 and PM10 (particularly 60 days preconception – month of conception) was associated with increased risk of hypothyroidism |
| Wang et al. [54] | Yes | No |
↓ Increased exposure to PM2.5 was associated with decreased maternal FT4 concentration. Increased exposure to PM2.5 components (BC and NH4+) was associated with decreased maternal FT4 concentration ⦸ No statistically significant association between exposure to PM2.5 and its components and neonatal TSH concentration |
| Zeng et al. [55] | -- | Yes |
↑ Increased exposure to PM2.5 was associated with higher odds of abnormal fetal TSH concentration ⦸ No statistically significant association between exposure to PM2.5 and odds of abnormal fetal FT3 or FT4 concentration |
| Zhang et al. [56] | Yes | -- |
↓ Increased exposure to PM2.5 was associated with decreased FT4 and FT4/FT3 ratio concentration ⦸ No statistically significant association was found between exposure to PM2.5 and FT3 and TSH concentration. No statistically significant association was found between PM10 and any of the thyroid hormones measured |
| Zhao et al. [57] | Yes | -- |
↑ Increased exposure to PM2.5 was associated with an increased risk in hypothyroxinemia ↓ Increased exposure to PM2.5 (particularly in the second trimester) and NO2 (particularly in the first trimester) was associated with decreased FT4 concentration ⦸ No statistically significant association was found between PM2.5 and NO2 and TSH concentration. There was no statistically significant association found between NO2 and risk of hypothyroxinemia |
| Zhou et al. [58] | Yes | -- |
↑ Increased exposure to PM2.5 was associated with increased TSH concentration. Increased exposure to constituent Al and Si was associated with increased FT4 concentration ↓ Increased exposure to PM2.5 was associated with decreased FT4 and FT4/FT3 ratio concentration. Increased exposure to Zn was associated with decreased FT4 concentration. Increased exposure to K, Mn, and Zn weas associated with decreased FT4/FT3 ratio concentration ⦸ No statistically significant association was found between PM2.5 and inorganic constituents and FT3 concentration |
Symbols: –, not evaluated; ↑, positive association; ↓, inverse association; ⦸, no statistically significant association