Table 1.

Baseline Characteristics of Participants by Breast Cancer Diagnosis Status, Shanghai Women's Health Study, 1997–2008

Characteristic	Cases (n = 718)		Noncases (n = 72,519)		P Valuea
	Mean (SD)	%	Mean (SD)	%
Age at baseline, years	52.7 (8.8)		52.5 (9.1)		0.46
Age at menarche, years	14.7 (1.8)		14.9 (1.7)		0.003
Ever parous		95.4		96.7	0.05
Age at first livebirth, years	26.5 (4.14)		25.6 (4.1)		<0.0001
Postmenopausal		51.9		51.1	0.69
Age at menopause, years	49.3 (4.0)		49.1 (4.0)		0.37
Ever use of hormone replacement therapy		2.7		2.1	0.49
History of fibroadenoma		6.8		3.3	<0.0001
Family history of breast cancer		3.6		1.8	0.0004
Height, m	1.575 (0.055)		1.581 (0.056)		0.005
Waist-to-hip ratio	0.813 (0.052)		0.811 (0.054)		0.17
Body mass index, kg/m2	24.2 (3.4)		24.0 (3.4)		0.08
Educational attainment					<0.0001
College or above		19.1		13.5
High school		35.0		27.9
Middle school		32.5		37.2
Less than middle school		13.4		21.5
Household income
High		24.5		27.6	0.11
Middle		39.0		38.9
Low		36.5		33.5
Ever smoked regularly		2.0		2.8	0.18
Ever drank alcohol regularly		2.1		2.3	0.78
Physical activity, MET-hours/week per year	102 (44)		107 (45)		0.13
Ever used a B vitamin supplement		13.7		10.3	0.003
Daily dietary intake
Energy, kcal	1,674 (373)		1,674 (394)		0.76
Vegetables, g	299 (162)		296 (169)		0.43
Fruits, g	265 (179)		264 (179)		0.83
Red meat, g	48.4 (33.4)			50.9 (36.1)		0.79
Fat, g	29.2 (12.4)		29.4 (13.0)		0.87

Abbreviations: MET, metabolic equivalent; SD, standard deviation.

^aP values are from t tests for log-transformed continuous variables, F tests for energy-adjusted least-squares means for log-transformed dietary intakes, and χ² tests for categorical variables.