TABLE 1.
Geographical differences in physiological zinc levels.
| Country | Gender*† (male: female) | Age in years* | Source | ASD mean zinc level | Control mean zinc level | p-value | References |
| Africa | |||||||
| Egypt | 3:1 | 4.1 ± 0.8 | Hair | 304.99 ± 25.8 μg/mg | 419.5 ± 45.96 μg/mg | n/a | Eman Elsheshtawy et al., 2011 |
| Antarctica—N/A | |||||||
| Asia | |||||||
| China | 4:1 | 3.78 (SD 1.22) | Serum | 78.7 (SD 7.0) μg/dl | 87.7 (SD 8.7) μg/dl | <0.001 | Li et al., 2014 |
| India | 4:1 | 4–12 | Hair | 130.46 (SD 15.65) μg/g | 171.68 (SD 20.60) μg/g | <0.01 | (Lakshmi Priya and Geetha, 2011) |
| Nails | 150.83 (SD 18.09) μg/g | 193.98 (SD 23.27) μg/g | <0.01 | Lakshmi Priya and Geetha, 2011 | |||
| Japan | 3.8:1 | 0–15 | Hair | ∼30% of ASD patients had a > 2 SD lower zinc concentration than reference | 129 (range 86.3–193) ppm | Yasuda and Tsutsui, 2013 | |
| Oman | 4.4:1 | 3–14 (mean 5.3) | Hair | Median 5.4 (quartile 0.82) μg/g | Median 2.9 (quartile 2.2) μg/g | 0.0001 | Al-Farsi et al., 2013 |
| Saudi Arabia | 5.3:1 | 3–9 | Hair | 67.04 (SD 23.78) mg/kg | 110–227 mg/kg | n/a | Blaurock-Busch et al., 2012 |
| Australia—N/A | |||||||
| Europe | |||||||
| Ireland (Northern) | 7.2:1 | 2–18 | Serum | 11.68 (SD 1.7) μmol/L | 11.63 (SD 2.1) μmol/L | 0.86 | Sweetman et al., 2019 |
| Romania | Not reported | 5.83 ± 3.10 | Whole blood | 5.54 (SD 0.78) μg/ml | 6.14 (SD 0.76) μg/ml | 0.005 | Craciun et al., 2016 |
| United Kingdom | 3.8:1 | 2–16 (mean 7.0) | Serum | 10.01 (SD 1.52) μmol/L | 11.76 (SD 2.14) μmol/L | <0.001 | Goyal et al., 2019 |
| Italy | 3:1 | 2–6 | Serum | 1021.52 (SD 100.76) ng/g | 808.03 (SD 131.89) ng/g | 0.01 | Vergani Lauraad et al., 2011 |
| 5.3:1 | 9.00 ± 4.05 | Hair | Median 149 (25th to 75th percentile 89.00—187.75) μg/g | Median 143(25th to 75th percentile 105.50—166.35) μg/g | 0.428 | Giuseppe De Palma et al., 2011 | |
| Slovenia | 7.8:1 | 1–16 | Serum | 10.74 (SD 1.81) μmol/L | 12.10 (SD 1.52) μmol/L | 0.007 | Marta Macedoni-Lukšič et al., 2014 |
| Russia | Not reported | 2–9 (mean 5.12 ± 2.36) | Hair | Median 124.6 (25th to 75th percentile 77.0–174.2) μg/g | Median 113.3 (25th to 75th percentile 69.4–166.3) μg/g | 0.365 | Skalny et al., 2017 |
| North America | |||||||
| United States | 3.5:1 | 6.3 (SD 3.67) | Serum | 76.89 (SD 14.1) μg/dl | Reference 66 μg/dl | n/a | Faber et al., 2009 |
| 6.2:1 | 11.7 ± 5.62 | Serum | 78.36 (SD 20.32) mg/dL | 84.42 (SD 24.18) mg/dL | 0.3541 | Russo and Devito, 2011 | |
| Canada | 4:1 | 3.90 ± 1.68 | Red-cell | 134.95 (SD 23.94) μmol/L | 148.27 (SD17.09) μmol/L | 0.08 | Joan Jory, 2008 |
| South America | |||||||
| Brazil | Not reported | <18 | Serum | 105 (SD 0.73) mg/dl | Not reported. | n/a | Saldanha Tschinkel et al., 2018 |
| Venezuela | Not reported | Not reported | Serum | 180.50 ± 57.72 μg/dl | 219.49 ± 72.10 μg/dl | N.S. | Semprún-Hernández et al., 2012 |
*For studies that list control and ASD patient age/gender separately, ASD patient information is reported in this table. †Gender ratios were calculated from reported numbers for simplicity. SD denotes standard deviation and variance reported are as published in the literature. If variance was not specified as standard error or deviation, variance is reported as mean ± variance.