Table 1.
Estimated relative risks for five lifestyle-related risk factor and breast cancer
| Risk factor | RR (95 % CI)a | Mean level within risk category | Comment | Source |
|---|---|---|---|---|
| BMI (kg/m2) | Continuous RR of 1.13 (95 % CI 1.08–1.18) per 5 kg/m2 | World Cancer Research Fund [6] | ||
| <25 | Reference | 21.9 kg/m2 | ||
| 25–30 | 1.15 (1.09–1.21) | 27.6 kg/m2 | ||
| >30 | 1.33 (1.19–1.49) | 33.8 kg/m2 | ||
| Physical inactivity | Days per week of at least 30 min of moderate intensity physical activityb. Continuous RR of 1.05 (95 % CI 1.03–1.07) per 2 h activity/week. | Wu et al. [7] | ||
| Active 5 days/week | Reference | 170 min/dayc | The reference category is based on (inter)national guidelines for physical activity [39]. | |
| Active 3–4 days/week | 1.06 (1.03–1.08) | 152 min/dayc | ||
| Active 1–2 days/week | 1.07 (1.04–1.10) | 147 min/dayc | ||
| Inactive | 1.34 (1.19–1.51) | 73 min/dayc | ||
| Alcohol (glass/day) | Continuous RR of 1.08 (95 % CI 1.05–1.10) per glass/day | World Cancer Research Fund [6] | ||
| Never drinker | Reference | 0 glasses/day | ||
| <1 | 1.05 (1.03–1.06) | 0.5 glasses/day | ||
| 1–3 | 1.20 (1.12–1.28) | 1.9 glasses/day | ||
| 4+ | 1.64 (1.35–1.97) | 5.2 glasses/day | ||
| Smoking | Categorical RR | Gaudet et al. [5] | ||
| Never | Reference | |||
| Past | 1.09 (1.04–1.15) | |||
| Current | 1.12 (1.08–1.16) | |||
| Dietary fibre (g/1000 kJ/day) | Continuous RR of 0.95 (95 % CI 0.91–0.98) per 10 g/day | Aune et al. [4] | ||
| >3.4 | Reference | 27 g/day | The reference is based on (inter)national recommendations for dietary fibre intake [40, 41] | |
| 2–3.4 | 1.03 (1.01–1.06) | 21 g/day | ||
| <2 | 1.07 (1.03–1.13) | 14 g/day |
For BMI, physical inactivity, alcohol and fibre intake, a continuous RR available from the literature was converted in an RR that matched the mean level of exposure in each risk factor category as observed from the population exposure rates. For example, based on the literature-derived RR for overweight/obesity of 1.13 per five units of increase in BMI, and a mean BMI of 21.9 kg/m2 in the reference category, 27.6 kg/m2 in the overweight category, and 33.8 kg/m2 in the obese category, the risk category associated RRs compared to the reference are 1.13(27.6−21.9)/5 = 1.15, and 1.13(33.8−21.9)/5 = 1.33 (outcome based on the calculation by using exact numbers)
aRelative risk (RR) and 95 % confidence interval (95 % CI)
bThe questionnaire included both occupational and non-occupational activities
cAverage number of minutes per week were derived from activity diaries which were filled in by a subsample of participants. Reported activity in the diaries includes all types of physical activity, irrespective of intensity level