Table 1. Characteristics of included studies in the meta-analysis.

First Author	Region	Study design	Publication year	Relationship between DR and SCH	Sample size	Age(years)	SCH sample	DR sample
Kim Bo-Yeon7	Korea	Case control	2011	YES	489	61.7 ± 9.8	61	207
Chen HS8	Taiwan	Case control	2007	NO	588	67.2 ± 10.8	41	158
Yang Jinkui11	China	Case control	2010	YES	327	61.0 ± 13.7	127	158
Chen Jihai12	China	Case control	2012	YES	400	75.53 ± 6.53	45	29
Guo Dan13	China	Case control	2012	YES	162	55.84 ± 13.03	40	30
Zheng Yongqiang14	China	Case control	2012	NO	138	60.2 ± 11.8	28	39
Yang Guangran53	China	Case control	2010	YES	371	59.94 ± 10.61	83	187
Tang Jiandong54	China	Case control	2012	YES	1156	64.6 ± 10.2	164	610