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Table 2 Cox Proportional Hazard Ratios (HRs) of Mortality Because of Cardiovascular Disease and Cancer According to Age at First Birth, the Ohsaki Cohort, Japan, 1995–2008

From: Age at first birth and long-term mortality for mothers: the Ohsaki cohort study

  Age at first birth (years)
  ≤19 20–24 25–29 ≥30
  (n = 498) (n = 13,607) (n = 5,625) (n = 894)
Person-years 5,347 153,247 64,446 9,881
All-cause
 No. of deaths 76 1352 617 120
 Crude HR (95% CI) 1.62 (1.29–2.04) 1.00 (referent) 1.08 (0.99–1.19) 1.38 (1.15–1.67)
p-value <0.01   0.10 <0.01
 Age at baseline adjusted HR (95% CI) 1.35 (1.07–1.70) 1.00 (referent) 1.05 (0.95–1.15) 1.30 (1.08–1.57)
p-value 0.01   0.34 <0.01
 Multivariate HRa (95% CI) 1.17 (0.92–1.49) 1.00 (referent) 1.09 (0.99–1.20) 1.33 (1.08–1.62)
p-value 0.21   0.09 <0.01
Cancer
 No. of deaths 22 381 178 35
 Crude HR (95% CI) 1.66 (1.08–2.55) 1.00 (referent) 1.11 (0.93–1.33) 1.43 (1.01–2.02)
p-value 0.02   0.25 0.04
 Age at baseline adjusted HR (95% CI) 1.50 (0.98–2.31) 1.00 (referent) 1.08 (0.90–1.29) 1.37 (0.97–1.94)
p-value 0.06   0.42 0.07
 Multivariate HRa (95% CI) 1.31 (0.83–2.06) 1.00 (referent) 1.12 (0.93–1.34) 1.45 (1.00–2.10)
p-value 0.25   0.25 0.051
CVD
 No. of deaths 27 468 195 38
 Crude HR (95% CI) 1.66 (1.13–2.45) 1.00 (referent) 0.99 (0.84–1.17) 1.26 (0.91–1.76)
p-value 0.01   0.90 0.17
 Age at baseline adjusted HR (95% CI) 1.32 (0.89–1.94) 1.00 (referent) 0.96 (0.81–1.14) 1.19 (0.85–1.65)
p-value 0.17   0.64 0.31
 Multivariate HRa (95% CI) 1.11 (0.74–1.67) 1.00 (referent) 0.97 (0.81–1.16) 1.13 (0.77–1.62)
p-value 0.62   0.72 0.51
Other
 No. of deaths 27 503 244 47
 Crude HR (95% CI) 1.55 (1.05–2.28) 1.00 (referent) 1.15 (0.99–1.34) 1.46 (1.08–1.97)
p-value 0.03   0.07 0.01
 Age at baseline adjusted HR (95% CI) 1.25 (0.85–1.83) 1.00 (referent) 1.11 (0.96–1.30) 1.37 (1.01–1.84)
p-value 0.26   0.16 0.04
 Multivariate HRa (95% CI) 1.11 (0.74–1.65) 1.00 (referent) 1.20 (1.02–1.41) 1.43 (1.03–1.99)
p-value 0.61   0.03 0.03
  1. Note. CI confidence interval, CVD cardiovascular disease, HR hazard ratio
  2. a The multivariate HR has been adjusted for age at baseline (continuous variable), number of births (1, 2, 3, or ≥4), use of oral contraceptives (yes or no), consumption of green vegetables, carrot or pumpkin, orange (for each food, ≤1–2 times per month, 1–2 times per week, 3–4 times per week, or almost every day), consumption of coffee (<1, 1–2, 3–4, or ≥5 cups per day), smoking status (never, former, or currently smoking), alcohol drinking (never, former, or currently drinking), body mass index at baseline in kg/m2 (<18.5, 18.5–24.9, or ≥25.0), increase in body weight since age 20 years (<10.0 or ≥10.0 kg), walking duration (<1 or ≥1 h per day), sleeping time in hours per day (continuous variable), defecation frequency (≥1 time per day, 1 time per 2–3 days, 1 time per 4–5 days or ≤1 time per 6 days), years of education (<10, 10–12, or ≥13 years), ikigai (yes, uncertain, or no), perceived mental stress (high, moderate, or low), and history of diabetes (yes or no)