Table 2. Subgroup analyses of plasma folate and breast cancer.

Analysis specification	No. of studies	OR(95% CI)	Heterogeneity		P
			I 2	P
Highest vs lowest
All studies	12	0.98(0.82-1.17)	63.0%	0.002	0.822
Case-control	10	0.93(0.77-1.13)	63.4%	0.003	0.488
Cohort	2	1.63(0.61-4.37)	67.9%	0.078	0.331
Increment of 5 ng/ml
All studies	9	0.99(0.94-1.04)	71.4%	0.000	0.654
Case-control	7	0.96(0.90-1.03)	74.0%	0.001	0.246
Cohort	2	1.10(0.90-1.36)	70.0%	0.068	0.346
Menopausal status
Premenopausal	6	1.05(0.89-1.24)	24.1%	0.253	0.593
Postmenopausal	6	0.98(0.86-1.11)	17.5%	0.300	0.722
Receptor tumor status
ER+	3	1.11(0.72-1.71)	78.6%	0.009	0.649
ER-	3	0.94(0.68-1.30)	0.0%	0.455	0.698
PR+	3	1.07(0.67-1.71)	77.6%	0.012	0.776
PR-	3	1.02(0.79-1.32)	0.0%	0.987	0.864
ER+/PR+	2	1.26(0.80-1.98)	72.3%	0.057	0.314
ER-/PR-	2	1.08(0.69-1.68)	0.0%	0.642	0.750
HER2+	2	1.18(0.74-1.89)	0.0%	0.885	0.486
HER2-	2	1.02(0.74-1.40)	23.1%	0.254	0.912
Geographic location
Europe	4	1.00(0.86-1.17)	14.4%	0.320	0.976
America	5	1.10(0.83-1.46)	64.8%	0.023	0.505
Asia	1	0.52(0.26-1.04)	.%	.	0.066

Abbreviations: OR, odds ratio; CI, confidence interval.