Table 4.
Associations of parity and lactation patterns with incident clinical fractures *
| Predictor | Univariate model† | Multivariable-adjusted model‡ | ||
|---|---|---|---|---|
| HR (95% CI)§ | p | HR (95% CI) | p | |
| Parity characteristics | ||||
| # pregnancies lasting >6 months | 0.02 | 0.14 | ||
| Never pregnant | Reference** (1.00) | Reference (1.00) | ||
| Never had term pregnancy lasting ≥6 months | 0.81 (0.59–1.12) | 0.69 (0.43–1.09) | ||
| 1 | 1.03 (0.84–1.25) | 1.22 (0.96–1.55) | ||
| 2 | 0.87 (0.74–1.03) | 1.01 (0.83–1.23) | ||
| 3 | 0.89 (0.76–1.05) | 0.94 (0.77–1.16) | ||
| 4 | 0.92 (0.77–1.10) | 0.97 (0.78–1.21) | ||
| 5+ | 1.10 (0.92–1.32) | 1.00 (0.80–1.25) | ||
| How many times pregnant | 0.20 | 0.78 | ||
| None | Reference (1.00) | Reference (1.00) | ||
| 1 | 1.00 (0.81–1.24) | 1.17 (0.91–1.51) | ||
| 2 | 0.93 (0.79–1.10) | 1.03 (0.84–1.27) | ||
| 3 | 0.86 (0.73–1.02) | 0.97 (0.79–1.19) | ||
| 4 | 0.92 (0.77–1.09) | 0.99 (0.80–1.23) | ||
| 5 | 0.93 (0.76–1.13) | 0.98 (0.77–1.24) | ||
| 6 | 1.01 (0.81–1.27) | 0.92 (0.69–1.23) | ||
| 7 | 0.96 (0.72–1.28) | 0.86 (0.60–1.23) | ||
| 8+ | 1.22 (0.95–1.56) | 0.98 (0.71–1.35) | ||
| Age at first birth (years) | 0.06 | 0.40 | ||
| Never pregnant/No pregnancy lasting ≥6 months | Reference (1.00) | Reference (1.00) | ||
| <20 | 0.82 (0.67–0.99) | 1.08 (0.84–1.38) | ||
| 20 – 29 | 0.97 (0.85–1.12) | 1.02 (0.86–1.22) | ||
| 30+ | 1.09 (0.89–1.32) | 1.19 (0.94–1.50) | ||
| Lactation pattern among participants who had been pregnant (n=83,563) | ||||
| Breastfed for at least 1 month | 0.71 | 0.51 | ||
| No | Reference (1.00) | Reference (1.00) | ||
| Yes | 1.02(0.92–1.12) | 0.96 (0.86–1.08) | ||
| How many children breastfed? | 0.38 | 0.82 | ||
| None | Reference (1.00) | Reference (1.00) | ||
| 1–2 | 0.99(0.89–1.10) | 0.96(0.84–1.09) | ||
| 3–5 | 1.05(0.92–1.19) | 0.95(0.81–1.11) | ||
| 6+ | 1.28(0.94–1.76) | 1.10(0.74–1.62) | ||
| How old when first breastfed? (years) | 0.70 | 0.69 | ||
| Never breastfed | Reference (1.00) | Reference (1.00) | ||
| <20 | 0.97(0.80–1.18) | 1.02(0.80–1.30) | ||
| 20 – 24 | 1.03(0.91–1.16) | 0.96(0.83–1.11) | ||
| 25 – 29 | 1.02(0.89–1.17) | 0.91(0.77–1.08) | ||
| 30 – 34 | 1.13(0.91–1.39) | 1.13(0.89–1.44) | ||
| 35 – 39 | 0.85(0.56–1.29) | 0.87(0.55–1.40) | ||
| 40 – 44 | 0.22(0.03–1.53) | 0.28(0.04–2.02) | ||
| 45+ | NA | NA | ||
| How old when last breastfed? (years) | 0.29 | 0.91 | ||
| Never breastfed | Reference (1.00) | Reference (1.00) | ||
| <20 | 0.92(0.66–1.29) | 1.03(0.69–1.56) | ||
| 20 – 24 | 0.99(0.85–1.17) | 0.93(0.77–1.14) | ||
| 25 – 29 | 0.94(0.82–1.08) | 0.98(0.83–1.16) | ||
| 30 – 34 | 1.07(0.93–1.23) | 0.97(0.82–1.15) | ||
| 35 – 39 | 1.04(0.86–1.25) | 0.87(0.70–1.09) | ||
| 40 – 44 | 1.39(1.04–1.86) | 1.14(0.82–1.60) | ||
| 45+ | 1.50(0.56–4.00) | 1.08(0.35–3.36) | ||
| Total number of months breastfed | 0.83 | 0.62 | ||
| Never breastfed | Reference (1.00) | Reference (1.00) | ||
| 1–6 | 1.03(0.92–1.15) | 0.96(0.84–1.10) | ||
| 7–12 | 0.98(0.84–1.14) | 0.92(0.76–1.11) | ||
| 13–23 | 0.98(0.83–1.17) | 0.93(0.76–1.15) | ||
| 24+ | 1.11(0.91–1.36) | 1.12(0.88–1.42) | ||
Cox proportional hazards regression models were used. Incident clinical fractures were defined as any clinical fracture with the exception of fractures of the fingers and toes, ribs, sternum/chest, skull/face, and cervical vertebrae.
Includes predictor only without any covariates
Includes the following covariates: age, race/ethnicity, education, smoking status, alcohol consumption, hysterectomy, bilateral oophorectomy, years since menopause, previous fracture age 55+, parental history of fracture, number of falls in the past 12 months, estrogen use, estrogen route of delivery, recency of estrogen use, use of prescription osteoporosis medication, use of aromatase inhibitors, tamoxifen use, antidepressant use, corticosteroid use, proton pump inhibitor use, anti-epileptic use, anti-neoplastic use, thiazolidinedione use, body mass index, total energy expenditure per week from physical activities (log-transformed), total calcium intake (log -transformed), total vitamin D intake (log-transformed) at baseline, and weight change since age 35.
HR denotes hazard ratio; CI denotes confidence interval.
Ref denotes reference group.