American Association for Cancer Research

Table 1.

Characteristics of women according to whether they had ≤30% or ≥70% of the breast showing mammographic densities

	Mammographic densities^*
		≤30% (n = 287)	≥70% (n = 256)
Age, y (mean ± SD)	51.4 ± 5.7	46.1 ± 4.5
Body mass index, kg/m² (mean ± SD)	28.9 ± 6.0	23.3 ± 3.1
Age at menarche, y (mean ± SD)	12.5 ± 1.6	12.7 ± 1.5
Parity (mean ± SD)	3.0 ± 1.7	2.1 ± 1.4
Age at first birth,^† y (mean ± SD)	23.2 ± 3.9	24.7 ± 4.8
Oral contraceptive use (%)	55.4	70.1
Menopausal status (%)
Premenopausal	31.4	75.3
Perimenopausal	7.0	4.7
Postmenopausal	61.7	20.0
Hormone replacement therapy use (%)^‡	41.3	49.0
Family history of breast cancer^§ (%)	23.2	32.0
Age when leaving full time school, y (mean ± SD)	18.3 ± 2.3	19.3 ± 2.7
Daily average alcohol intake, drinks (mean ± SD)	0.30 ± 0.57	0.55 ± 0.89
Daily average caloric intake, kcal (mean ± SD)	1,964 ± 730	1,994 ± 760
Smoking status (%)
Nonsmoker	43.6	45.7
Former smoker	37.3	27.7
Current smoker	19.2	26.6

	Mammographic densities^*
		≤30% (n = 287)	≥70% (n = 256)
Age, y (mean ± SD)	51.4 ± 5.7	46.1 ± 4.5
Body mass index, kg/m² (mean ± SD)	28.9 ± 6.0	23.3 ± 3.1
Age at menarche, y (mean ± SD)	12.5 ± 1.6	12.7 ± 1.5
Parity (mean ± SD)	3.0 ± 1.7	2.1 ± 1.4
Age at first birth,^† y (mean ± SD)	23.2 ± 3.9	24.7 ± 4.8
Oral contraceptive use (%)	55.4	70.1
Menopausal status (%)
Premenopausal	31.4	75.3
Perimenopausal	7.0	4.7
Postmenopausal	61.7	20.0
Hormone replacement therapy use (%)^‡	41.3	49.0
Family history of breast cancer^§ (%)	23.2	32.0
Age when leaving full time school, y (mean ± SD)	18.3 ± 2.3	19.3 ± 2.7
Daily average alcohol intake, drinks (mean ± SD)	0.30 ± 0.57	0.55 ± 0.89
Daily average caloric intake, kcal (mean ± SD)	1,964 ± 730	1,994 ± 760
Smoking status (%)
Nonsmoker	43.6	45.7
Former smoker	37.3	27.7
Current smoker	19.2	26.6

Percentage of the breast showing mammographic densities.

In parous women.

In postmenopausal women.

Mother, sister, daughter, maternal or paternal grandmother, or aunt.