Table 1. Characteristics of the included studies about serum copper levels and cervical cancer risk.

Study, year	Country	Age (range or Mean ± SD)	Study type	Study quality scores	Cervical cancer cases		Controls
					n	Serum copper: mean ± SD	n	Serum copper: mean ± SD
Arumanayagam et al., 1993 [8]	China	58.7± 1.83	HBCC	7	57	19.1 ± 0.55 (μmol/l)	24	18.2 ± 0.75 (μmol/l)
Cetinkaya et al., 1988 [9]	Turkey	NA	PBCC	7	9	1.69 ± 0.6 (μg/ml	20	0.44 ± 0.46 (μg/ml)
Chen et al., 1990 [10]	China	25–70	HBCC	7	99	117.1 ± 14.6 (μg/ml)	50	109.4 ± 17.4 (μg/ml)
Cunzhi et al., 2003 [11]	China	30–65	PBCC	6	40	19 ± 7 (μmol/l)	50	14 ± 4 (μmol/l)
Fu et al., 2009 [12]	China	31–70	PBCC	7	74	18.96 ± 3.25 (μmol/l)	180	15.78 ± 3.88 (μmol/l)
Grail et al., 1986 [13]	U.K.	25–60	PBCC	8	24	1.47 ± 0.26 (mg/l)	21	1.25 ± 0.16 (mg/l)
Kim et al., 2003 [19]	Korea	35–74	HBCC	7	36	101.6 ± 5.25 (μg/dl)	44	101.5 ± 5.47 (μg/dl)
Naidu et al., 2007 [14]	India	25–65	PBCC	8	30	117.4 ± 12.26 (μg%)	30	109.7 ± 10.85 (μg%)
Ramteke et al., 2015 [15]	India	35–75	PBCC	8	50	156.9 ± 3.4 (μg/dl)	50	107.2 ± 1.79 (μg/dl)
Subramanyam et al., 2013 [20]	India	30–75	PBCC	7	104	78.15 ± 2.8 (μg/dl)	50	98.76 ± 2.43 (μg/dl)
Wang et al., 2010 [16]	China	25–60	PBCC	7	41	14.23 ± 3.15 (μmol/l)	260	12.73 ± 2.56 (μmol/l)
Yu et al., 2016 [21]	China	36–65	PBCC	7	70	12.39 ± 2.1 (μmol/l)	150	48.74 ± 6.5 (μmol/l)
Zhang et al., 1996 [17]	China	32–61	PBCC	6	55	24.93 ± 6.05 (μmol/l)	35	19.31 ± 2.46 (μmol/l)
Zhang et al., 2015 [18]	China	32–70	PBCC	7	58	50.9 ± 4.5 (μmol/l)	50	10.3 ± 4 (μmol/l)

Abbreviations: HBCC, hospital-based case–control study; PBCC, population-based case–control study.