Supplemental Table S1 Characteristics of the 35 excluded studies

Study / Reason for exclusion
Missing Cu plasma/serum levels
Awadallah et al. Z Ernahrungswiss 1978, 17, 79-83 / Without intact paper
Awadallah et al. Z Ernahrungswiss 1978, 17, 72-78. / Without intact paper
Hill et al. JAMA 1987 15, 257, 2593. / A letter to the editors
Smith et al. J Trace Elem Electrolytes Health Dis 1988, 2, 239-243. / Without intact paper
Raz et al. Diabetes Res 1989, 10, 21-24. / Without intact paper
Behall et al. Adv Exp Med Biol. 1990, 270, 7-16. / Missing healthy controls
Chen et al. Zhonghua Yi Xue Za Zhi (Taipei) 1991, 48, 431-438. / Without intact paper
Car et al. Biol Trace Elem Res 1992, 32, 325-329. / Without intact paper
Cunningham et al. Metabolism 1994, 43, 1558-1562. / Without intact paper
Isbir et al. Diabetes Res 1994, 26, 41-45 / Without intact paper
Ruiz et al. J Trace Elem Med Biol 1998, 12, 91-95. / Without intact paper
Terres-Martos. J Trace Elem Med Biol 1998, 12, 44-49. / Without intact paper
Aguilar et al. Ann Nutr Metab 2007, 51, 402-406 / What body fluids the authors quantified Cu level with is confusing because the descriptions between “Analytical Methods” and “Table 2” are different.
Kazi et al. Biol Trace Elem Res 2008, 122, 1-18 / Cu levels in whole blood
Prabodh et al. Biol Trace Elem Res 2011, 142, 29-35. / Cu levels in whole blood
Ferdousi et al. Mymensingh Med J 2012, 21, 475-478. / Without intact paper
Savu et al. J Int Med Res 2012, 40, 709-716 / The characteristics of diabetes patients who were included in the Cu level analysis were not consistent with those shown in the article.
Forte et al. Biol Trace Elem Res 2013, 156, 79–90 / Cu levels in whole blood
Basaki et al. Biol Trace Elem Res 2012, 148, 161-164 / Missing the units of Cu levels
Rambousková et al. Arch Gerontol Geriatr 2013, 56, 389-94 / Cu levels in whole blood
Salmonowicz et al. Adv Clin Exp Med 2014, 23, 259–268 / Only the percentage of Cu levels
Missing diagnosis of diabetes type in each participant
Mateo et al. Biomedicine 1978, 29, 56-8 / Missing diagnosis of diabetes type
Williams et al. Analyst 1995, 20, 887-890 / Missing diagnosis of diabetes type
Chen et al. J Trace Elements Med Biol 2001, 14, 228-231 / Missing diagnosis of diabetes type
Yildirim et al. Ann N Y Acad Sci. 2007, 1100, 199-206. / Missing diagnosis of diabetes type
Prabodh et al. Biol Trace Elem Res 2011, 142, 29–35 / Missing diagnosis of diabetes type
Batista et al. Biol Trace Elem Res 2006, 112, 1-12 / Missing diagnosis of diabetes type

Supplemental Table S1 (continued)

Missing healthy controls
Khan et al. Biol Trace Elem Res 2015, 168, 321-329 / Unhealthy controls
Rotter et al. Int J Environ Res Public Health 2015, 12, 3944-3961. / Unhealthy controls
Smoking subjects
El Husseiny et al. Biol Trace Elem Res 2011, 143, 1451–1460 / Smoking interference
Gestational study
Hyvönen-Dabek et al. Clin Chem 1984, 30, 529-33. / Gestational interference
Not case-control study
Cunningham et al. Metabolism, 1995, 44, 996-999 / Not case-control study
Tison et al. Parkinsonism Relat Disord 1996, 2, 131-135. / Not case-control study
Cooper et al. Diabetes 2005, 54, 1468-1476 / Not case-control study
Leber et al. Eur J Clin Nutr 2012, 66, 1110-1115. / Not case-control study