Table 3.
Association of hair product use frequency, color of dyes, and duration of use with uterine cancer in the Sister Study
| Hair product usea | Person-years | Full cohort | Case | Age-adjusted HR (95% CI)c | Fully adjusted HR (95% CI)c,d |
|---|---|---|---|---|---|
| No. (%)b | No. (%)b | ||||
| Permanent dyes | |||||
| Frequency in the past 12 months prior to baseline | |||||
| Never | 162 425 | 14 795 (44.4) | 184 (49.9) | Referent | Referent |
| ≤4 times | 83 284 | 7740 (23.2) | 64 (17.3) | 0.80 (0.60 to 1.06) | 0.79 (0.59 to 1.05) |
| >4 times | 117 166 | 10 791 (32.4) | 121 (32.8) | 0.92 (0.73 to 1.16) | 0.98 (0.78 to 1.24) |
| Ptrende | .44 | .77 | |||
| Color used in the past 12 months prior to baseline | |||||
| Never | 162 425 | 14 795 (44.4) | 184 (49.9) | Referent | Referent |
| Light colorf | 107 507 | 9895 (29.6) | 98 (26.5) | 0.87 (0.69 to 1.10) | 0.93 (0.73 to 1.18) |
| Dark colorf | 111 846 | 10 401 (31.2) | 101 (27.4) | 0.92 (0.72 to 1.16) | 0.91 (0.72 to 1.16) |
| Duration of use, lifetime | |||||
| Never | 128 528 | 11 660 (35.4) | 151 (41.8) | Referent | Referent |
| <5 years | 61 572 | 5688 (17.3) | 48 (13.3) | 0.76 (0.55 to 1.06) | 0.75 (0.54 to 1.04) |
| 5 to <10 years | 55 141 | 5064 (15.4) | 50 (13.9) | 0.83 (0.60 to 1.14) | 0.84 (0.61 to 1.15) |
| ≥10 years | 113 108 | 10 494 (31.9) | 112 (31.0) | 0.80 (0.63 to 1.03) | 0.82 (0.64 to 1.05) |
| Ptrende | .10 | .14 | |||
| Semipermanent dyes | |||||
| Frequency in the past 12 months prior to baseline | |||||
| Never | 293 148 | 26 829 (80.5) | 307 (82.7) | Referent | Referent |
| ≤4 times | 41 738 | 3903 (11.7) | 35 (9.4) | 0.92 (0.65 to 1.31) | 0.91 (0.63 to 1.29) |
| >4 times | 27 852 | 2581 (7.7) | 29 (7.8) | 0.96 (0.65 to 1.40) | 0.98 (0.67 to 1.44) |
| Ptrende | .69 | .77 | |||
| Color used in the past 12 months prior to baseline | |||||
| Never | 293 148 | 26 829 (80.5) | 307 (82.7) | Referent | Referent |
| Light colorf | 25 324 | 2339 (7.0) | 19 (5.1) | 0.72 (0.45 to 1.14) | 0.73 (0.46 to 1.17) |
| Dark colorf | 46 522 | 4364 (13.1) | 44 (11.9) | 1.02 (0.74 to 1.40) | 1.03 (0.74 to 1.42) |
| Duration of use, lifetime | |||||
| Never | 249 458 | 22 877 (70.1) | 254 (71.1) | Referent | Referent |
| <5 years | 54 979 | 5014 (15.4) | 49 (13.7) | 0.94 (0.69 to 1.27) | 0.93 (0.69 to 1.27) |
| 5 to <10 years | 25 424 | 2326 (7.1) | 28 (7.8) | 1.08 (0.73 to 1.60) | 1.15 (0.78 to 1.70) |
| ≥10 years | 25 570 | 2414 (7.4) | 26 (7.3) | 0.91 (0.61 to 1.36) | 0.90 (0.60 to 1.35) |
| Ptrende | .78 | .85 | |||
| Straighteners, relaxers, or pressing products | |||||
| Frequency in the past 12 months prior to baseline | |||||
| Never | 333 535 | 30 329 (90.9) | 332 (89.7) | Referent | Referent |
| ≤4 times | 14 268 | 1464 (4.4) | 12 (3.2) | 1.06 (0.59 to 1.88) | 1.20 (0.63 to 2.29) |
| >4 times | 15 464 | 1572 (4.7) | 26 (7.0) | 2.19 (1.47 to 3.26) | 2.55 (1.46 to 4.45) |
| Ptrende | <.001 | .002 | |||
| Hair permanents or body waves | |||||
| Frequency in the past 12 months prior to baseline | |||||
| Never | 323 483 | 29 689 (89.0) | 316 (85.6) | Referent | Referent |
| ≤2 times | 21 293 | 1951 (5.8) | 23 (6.2) | 0.99 (0.65 to 1.52) | 0.92 (0.60 to 1.41) |
| >2 times | 18 486 | 1730 (5.2) | 30 (8.1) | 1.28 (0.87 to 1.89) | 1.11 (0.75 to 1.63) |
| Ptrende | .24 | .71 | |||
Missing: permanent dyes (2 cases, 137 overall); color of permanent dyes (4 cases, 168 overall); duration of permanent dye uses (10 cases, 557 overall); semipermanent dyes (150 overall); color of semipermanent dyes (2 cases, 172 overall); duration of semipermanent dyes use (14 cases, 832 overall); straighteners, relaxers, or pressing products (1 case, 98 overall); hair permanents or body waves (2 cases, 93 overall). CI = confidence interval; HR = hazard ratio.
Participants with complete confounder information.
Accounted for age by using age as the timescale, where the participants were followed from age at baseline until age at end of follow-up.
Adjusted for race and ethnicity (African American/Black, Hispanic/Latina non-Black, non-Hispanic White, other), education (high school or less, some college, college and above), body mass index (restricted cubic spline, continuous, kg/m2), physical activity (metabolic equivalent [MET] hours per week, continuous), menopausal status at enrollment (premenopausal, postmenopausal), parity (0, 1, 2, ≥3), smoking (never, past, or current), alcohol (never or past, current <1 drink, current ≥1 drinks), oral contraceptive use duration (none, <2 years, 2 to <10 years, ≥10 years), hormone replacement therapy (none, estrogen alone, estrogen plus progestin but never estrogen alone), age at menarche (<13 years, ≥13 years old).
Assessed using Wald tests for continuous variables of hair product use frequency and duration.
Hair color is nonexclusive: participants could be both light and dark users. Both colors were included in the models simultaneously.