Table 2.
Hazard Ratios and 95% confidence interval (CI) for association between stressful life events and breast cancer in the Women’s Health Initiative Observational Study
| Cases | Person-years | Age-adjusted | + Socio-demographic and health factorsa | + Gail model score and other breast cancer risk factorsb | + Behavioral factorsc | |||||
|---|---|---|---|---|---|---|---|---|---|---|
| Hazard Ratio | 95% CI | Hazard Ratio | 95% CI | Hazard Ratio | 95% CI | Hazard Ratio | 95% CI | |||
| Baseline Life Events N=84,334 | ||||||||||
|
| ||||||||||
| 0 | 519 | 140,456 | reference | reference | reference | reference | ||||
| 1 | 838 | 199,225 | 1.14 | (1.02,1.27) | 1.12 | (1.01,1.25) | 1.12 | (1.01,1.25) | 1.12 | (1.01,1.26) |
| 2 | 585 | 148,657 | 1.08 | (0.96,1.22) | 1.08 | (0.96,1.21) | 1.08 | (0.96,1.22) | 1.08 | (0.95,1.22) |
| 3 | 316 | 83,821 | 1.05 | (0.91,1.21) | 1.06 | (0.92,1.22) | 1.08 | (0.94,1.24) | 1.08 | (0.93,1.24) |
| 4+ | 223 | 65,468 | 0.97 | (0.82,1.13) | 0.98 | (0.83,1.15) | 1.02 | (0.86,1.19) | 1.02 | (0.87,1.21) |
| p-value (total/trend) | 0.076/0.53 | 0.20/0.86 | 0.30/0.82 | 0.33/0.85 | ||||||
|
| ||||||||||
| Baseline Life Events Weighted by Participant’s Appraisal of Stress N=84,334 | ||||||||||
|
| ||||||||||
| 0 | 519 | 140,456 | reference | reference | reference | reference | ||||
|
| ||||||||||
| 1–2 | 838 | 199,225 | 1.16 | (1.04,1.3) | 1.15 | (1.02,1.28) | 1.14 | (1.02,1.28) | 1.145 | (1.02,1.29) |
|
| ||||||||||
| 3 | 585 | 148,657 | 1.06 | (0.93,1.21) | 1.043 | (0.91,1.19) | 1.050 | (0.92,1.20) | 1.056 | (0.92,1.21) |
|
| ||||||||||
| 4–5 | 316 | 83,821 | 1.056 | (0.93,1.20) | 1.062 | (0.93,1.21) | 1.070 | (0.94,1.22) | 1.055 | (0.92,1.21) |
|
| ||||||||||
| >5 | 223 | 65,468 | 1.023 | (0.90,1.16) | 1.039 | (0.91,1.18) | 1.065 | (0.94,1.21) | 1.063 | (0.93,1.21) |
| p-value (total/trend) | 0.08/0.64 | 0.19/0.93 | 0.23/0.76 | 0.24/0.85 | ||||||
|
| ||||||||||
| Time-varying stressful life events N=84,334
| ||||||||||
| 0 | 625 | 172,152 | reference | reference | reference | reference | ||||
| 1 | 862 | 210,637 | 1.09 | (0.98,1.21) | 1.09 | (0.99,1.21) | 1.09 | (0.98,1.21) | 1.09 | (0.98,1.22) |
| 2 | 535 | 137,611 | 1.01 | (0.90,1.13) | 1.01 | (0.90,1.13) | 1.02 | (0.91,1.15) | 1.01 | (0.90,1.14) |
| 3 | 281 | 68,733 | 1.04 | (0.90,1.19) | 1.06 | (0.92,1.22) | 1.07 | (0.93,1.24) | 1.08 | (0.93,1.25) |
| 4+ | 178 | 48,494 | 0.91 | (0.77,1.08) | 0.93 | (0.79,1.11) | 0.96 | (0.81,1.14) | 0.97 | (0.81,1.16) |
| p-value (total/trend) | 0.18/0.35 | 0.24/0.58 | 0.38/0.87 | 0.36/0.91 | ||||||
|
| ||||||||||
| Cumulative stressful life events N=73,228 | ||||||||||
|
| ||||||||||
| 0 | 147 | 132,487 | reference | reference | reference | reference | ||||
| 0.5–1 | 652 | 133,645 | 1.09 | (0.91,1.30) | 1.08 | (0.90,1.29) | 1.08 | (0.90,1.29) | 1.037 | (0.86,1.25) |
| 1.5–2 | 477 | 103,623 | 1.04 | (0.86,1.25) | 1.04 | (0.86,1.25) | 1.04 | (0.86,1.26) | 1.032 | (0.85,1.25) |
| 2.5–3 | 207 | 47,047 | 1.01 | (0.82,1.25) | 0.99 | (0.80,1.23) | 1.01 | (0.82,1.26) | 0.987 | (0.79,1.23) |
| 3.5+ | 105 | 25,509 | 0.96 | (0.75,1.24) | 0.99 | (0.77,1.28) | 1.04 | (0.80,1.34) | 1.027 | (0.79,1.33) |
| p-value (total/trend) | 0.67/0.38 | 0.74/0.44 | 0.90/0.76 | 0.98/0.87 | ||||||
Note: The first p-value is the chi-square test of the overall association between classifications, i.e. between breast cancer incidence and stressful life events. We also show the p-value for a chi-squared test of linear trend which evaluates whether breast cancer risk increases with number of stressful life events.
Adjusted for age plus education (<high school, high school or equivalent, some college, >=college degree), ethnicity (AI/AN, Asian/PI, Caucasian, Black/AA, Hispanic, Other), diagnosis with diabetes (yes/no), and BMI (linear). Additional factors considered: income (don’t know/missing, <20K, 20K to < 50K, 50K to <100K, 100K+), insurance status (none, public, or private), cardiovascular disease (yes/no), previous other cancer diagnosis (yes/no), and hypertension (no, yes-untreated, yes-treated).
Adjusted for those on the left plus five-year breast cancer risk from Gail prediction (age, age at menarche, number of previous breast biopsies, presence of atypical hyperplasia on biopsy, age at first childbirth, number of first-degree relatives with a history of breast cancer, and the interactions between biopsies and age and between age at first childbirth and number of affected first-degree relatives) parity (no births,1,2,3,4,5+), history of hysterectomy/bilateral oopherectomy, OC use (never, >0 to <5 years, 5 to <10 years, and 10+ years), HRT use (never, >0 to < 5years, 5 to <10 years, 10+ years). Additional factors considered: number of months breast feeding (never,1–8 mo, >8 mo).
Adjusted for those on the left plus alcohol consumption (none, 0–1/day,1–2/day,2–3/day,>3/day), smoking (never, past, current), fat intake (<30% vs. >=30%), and annual mammography rate during follow-up. Additional factors considered: current physical activity (vigorous exercise 2+ days/week)