Body mass index had different effects on premenopausal and postmenopausal breast cancer risks: a dose-response meta-analysis with 3,318,796 subjects from 31 cohort studies

Table 1 Subgroup analysis showing differences between studies included in the meta-analysis (highest versus lowest BMI)

Variables	Number of studies	Number of cases	Test of association		Test of heterogeneity		Publication bias		P ^a
Variables	Number of studies	Number of cases	Pooled RR (95% CI)	P value	I ² (%)	P value	Begg’s Pvalue	Egger’s P value	P ^a
All	31	43,698	1.19(1.06–1.33)	0.002	67	<0.00001	0.696	0.542
Menopausal status									0.0006
Pre-^b	18	5588	0.94(0.81–1.11)	0.49	49	0.01	0.705	0.347
Post-^c	26	35,012	1.33(1.20–1.48)	<0.0001	66	<0.00001	0.113	0.603
Post- age									0.400
above 65	4	3580	1.53(1.39–1.68)	<0.0001	0	0.68	0.734	0.581
below 65	4	1346	1.35(1.04–1.76)	0.02	55	0.09	0.308	0.208
Post- ER status									<0.0001
ER + ^d	6	7776	1.32(1.23–1.42)	<0.0001	0	0.67	1.000	0.679
ER-^e	5	1109	0.87(0.72–1.05)	0.15	0	0.57	0.806	0.496
Post- HRT use									0.06
Never	8	8684	1.43(1.21–1.68)	<0.0001	55	0.03	0.902	0.811
Ever	4	2580	0.94(0.63–1.40)	0.76	61	0.05	0.734	0.669
Post- Area									0.0006
America	12	20,036	1.29(1.14–1.46)	<0.0001	63	0.002	0.945	0.912
Asia	5	2234	2.10(1.64–2.69)	<0.0001	0	0.8	0.806	0.152
Europe	9	12,742	1.19(0.98–1.43)	0.07	71	0.0006	0.917	0.046
Post- follow up years									0.610
Below 5	5	6482	1.21(0.97–1.51)	0.08	0	0.56	0.806	0.849
Above 5	21	28,730	1.29(1.19–1.41)	<0.0001	59	0.0003	0.415	0.792
Pre- follow up years									0.510
Below 5	3	1071	0.82(0.60–1.12)	0.22	33	0.23	1.000	0.190
Above 5	15	4517	0.92 (0.79–1.08)	0.32	41	0.05	0.921	0.202
Pre- Area									0.004
America	5	1322	1.10(0.77–1.57)	0.61	71	0.008	0.858	0.304
Asia	5	1179	1.23(0.95–1.59)	0.12	0	0.44	0.806	0.698
Europe	8	3087	0.79(0.70–0.88)	<0.0001	0	0.49	0.283	0.387

^a indicates that P value was used for comparing the differences among subgroups. ^b indicates premenopausal women, c indicates postmenopausal women, d indicates estrogen receptor positive status, e indicates estrogen receptor negative status

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