Table 1.

Age-Standardized Characteristics of 50,543 BWHS participants in 1997 according to hair relaxer use^a,b

	Never or light use (n = 5183)	Moderate use (n = 35,194)	Heavy use(n = 10,166)
Age (mean ± SD)	44.6 ± 12.0	40.5 ± 10.7	40.0 ± 9.2
Column %s
BMI at age 18, kg2/m
<20	42	40	40
20–24	43	44	45
≥25	13	14	14
Body Mass Index, kg/m2
<25	41	34	33
25–29	31	32	34
30–34	15	18	18
≥35	12	15	15
Parity
Nulliparous	32	32	33
1 child	22	23	23
2 children	23	24	25
≥3 children	22	21	19
Age at first birth (among parous women)
<20 years	31	32	32
20–24 years	36	34	35
≥25 years	31	32	32
Alcohol consumption, drinks/week
<1	74	72	72
1–6	21	23	23
≥7	3	4	4
Physical activity
< 1 h/week	58	60	63
1–4 hs/week	29	28	27
≥5 h/week	10	9	8
Age at menarche
≤11 years	26	29	29
12–13 years	53	52	52
≥14 years	21	19	18
Family history of breast cancer	10	9	9
Menopausal status
Premenopausal	74	74	73
Postmenopausal	19	19	20
Educational attainment (1995)
≤12 years	22	18	18
13–15 years	34	36	35
16 years	22	24	26
≥17 years	22	22	22
Region of residence (U.S.)
Northeast	28	28	22
South	24	31	38
Midwest	20	23	25
West	28	18	15
Ever use of postmenopausal hormones	4	4	4
Ever use oral contraceptives	80	85	88
Had mammogram between 1995 and 1997	51	53	53

^aAge standardized in 5 year intervals; all characteristics from 1997 unless noted otherwise; percentages may not add to 100 due to missing values.

^bNo or light use is 1–4 years, ≤2 times/year; heavy use is use for ≥15 years, ≥7 times/year; remainder are moderate users (1–4 years, >3 times/year; 4–14 years, any frequency; and ≥15 years, <7 times/year).