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Table 4 Multivariate HR of Mortality According to Age at First Birth by Generation, 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) p-interaction
Born year (Age at baseline)
  < 1935 (≥60)      0.33
 No. of deaths 68 1169 528 104
 Multivariate HRa (95% CI) 1.18 (0.91–1.52) 1.00 (referent) 1.11 (1.00–1.24) 1.52 (1.22–1.89)
p-value 0.21   0.049 <0.01
1935–1955 (40–59)
 No. of deaths 8 183 89 16
 Multivariate HRa (95% CI) 1.01 (0.49–2.08) 1.00 (referent) 1.30 (1.00–1.69) 1.43 (0.83–2.46)
p-value 0.99   0.051 0.20
Birth year of the first child
  < 1960      0.58
 No. of deaths 73 1203 486 72
 Multivariate HRa (95% CI) 1.18 (0.92–1.51) 1.00 (referent) 1.05 (0.94–1.17) 1.33 (1.03–1.72)
p-value 0.19   0.38 0.03
1960-
 No. of deaths 3 149 131 48
 Multivariate HRa (95% CI) 0.61 (0.19–1.94) 1.00 (referent) 1.26 (0.98–1.63) 1.45 (0.97–2.16)
p-value 0.40   0.07 0.07
  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)