Table 2.
Relative risks and changes in the prevalence (%) of breast cancer risk factors according to lifestyle changes from 1998 to 2015
| Relative risk (95% CI) | Prevalence (%) |
|||
|---|---|---|---|---|
| 1998 | 2015 | 2030 | ||
| Age at first birth (yr) | ||||
| ≤ 23 | 1.00 | 13.8 | 4.9 | - |
| 24-30 | 1.13 (0.98-1.32) | 66.7 | 36.5 | - |
| ≥ 31 | 1.27 (0.98-1.66) | 9.5 | 48.6 | - |
| Total period of breast feeding (mo) | ||||
| Never | 1.03 (0.87-1.21) | 89.8 | 62.1 | - |
| ≤ 6 | 1.28 (1.07-1.53) | 9.2 | 22.5 | - |
| > 6 | 1.00 | 1.0 | 15.4 | - |
| Obesity (kg/m2) | ||||
| BMI < 25 | 1.00 | 74.1 | 71.2 | - |
| BMI ≥ 25 | 1.40 (1.02-1.53) | 25.9 | 28.8 | - |
| Alcohol drinking | ||||
| No | 1.00 | 67.3 | 53.5 | - |
| Yes | 1.15 (0.72-2.66) | 32.7 | 46.5 | - |
| Oral contraceptive use | ||||
| Never | 1.00 | - | 84.3 | 84.3 |
| Ever | 1.31 (1.04-1.64) | - | 15.7 | 15.7 |
| Hormone replacement therapy use | ||||
| Never | 1.00 | - | 97.5 | 96.6 |
| Ever | 1.16 (0.36-3.87) | - | 2.5 | 3.4 |
This study assumed a latency period of about 15 years between the exposure of a risk factor and breast cancer development, except for oral contraceptive (OC) and hormone replacement therapy (HRT) use. We assumed the annual increasing rates for the future prevalence rates of OC and HRT use to be 0% and 2%, respectively, considering the trend for OC and HRT use during 2001-2015. CI, confidence interval; BMI, body mass index.