TABLE 1

Univariate and Multivariate Cox Proportional Hazard Models of Age at Menarche

CharacteristicsTotalMean Age at MenarcheaUnadjusted HR (95% CI)Adjusted HR (95% CI)b
Total319913.56
Demographic variables
 Year of birth
  1973–198059614.061.001.00
  1981–198569714.060.85 (0.75–0.96)*0.77 (0.67–0.88)**
  1986–199076213.481.26 (1.15–1.38)**1.12 (0.99–1.27)
  1991–199548213.001.69 (1.53–1.86)**1.51 (1.33–1.71)**
  1996–200466212.752.13 (1.87–2.41)**1.92 (1.70–2.17)**
  P trendc<.001<.001
 Region
  Northeastern area49113.451.001.00
  East coast66413.660.91 (0.80–1.03)0.83 (0.72–0.96)*
  Central area109613.471.03 (0.94–1.13)1.13 (1.03–1.25)*
  Western area94813.660.95 (0.84–1.08)1.02 (0.91–1.15)
 Ethnicity
  Han271013.521.001.00
  Minority45213.800.93 (0.83–1.05)0.99 (0.87–1.12)
  Missing3714.500.41 (0.17–0.94)*0.35 (0.17–0.72)*
Socioeconomic variables
 Rural or urban residency
  Rural228913.681.001.00
  Urban91013.201.32 (1.18–1.48)**1.26 (1.15–1.38)**
 Household income per person
  Q178514.031.001.00
  Q278613.601.19 (1.06–1.32)**1.06 (0.94–1.20)
  Q378613.481.32 (1.19–1.47)**1.03 (0.92–1.16)
  Q478413.121.59 (1.40–1.80)**0.96 (0.82–1.13)
  Missing5812.921.95 (1.40–2.73)**1.55 (1.09–2.20)*
  P trendc<.001.301
 Paternal education (y)
  ≤659913.911.001.00
  7–9124013.581.18 (1.06–1.31)*0.96 (0.86–1.06)
  10–1271313.481.30 (1.12–1.52)**0.98 (0.84–1.13)
  ≥136713.371.38 (1.22–1.55)**0.85 (0.72–1.00)*
  Missing17113.121.53 (1.34–1.74)**0.85 (0.63–1.16)
  P trendc<.001.239
 Maternal education (y)
  ≤6110113.871.001.00
  7–9111613.401.30 (1.18–1.43)**1.09 (0.97–1.22)
  10–1251213.421.39 (1.21–1.59)**1.16 (1.02–1.32)*
  ≥1316113.101.55 (1.28–1.89)**1.02 (0.80–1.29)
  Missing30913.281.37 (1.17–1.61)**0.72 (0.51–1.03)
  P trendc<.001.231
 Living with parents
  Without parents18012.871.001.00
  Father or mother29513.260.78 (0.63–0.97)*0.67 (0.47–0.95)*
  Father and mother270413.610.66 (0.54–0.79)**0.55 (0.31–0.98)*
  Missing2013.700.60 (0.39–0.92)*0.79 (0.50–1.25)
  P trendc<.001.072
Nutritional and lifestyle variables
 BMI
  Underweight28014.061.001.00
  Normal229013.541.40 (1.21–1.62)**1.41 (1.23–1.61)**
  Overweight13312.762.13 (1.66–2.72)**2.05 (1.63–2.57)**
  Obese6312.632.71 (1.83–4.01)**2.33 (1.58–3.42)**
  Missing43313.661.28 (1.04–1.57)*1.30 (1.06–1.59)*
  P trendc<.001<.001
 Energy intake (kcal/d)
  Low156313.481.001.00
  Normal98213.610.91 (0.82–1.00)1.04 (0.91–1.20)
  High53413.511.04 (0.94–1.14)1.29 (1.11–1.50)**
  Missing12014.190.67 (0.53–0.85)**0.69 (0.48–1.01)
  P trendc.856.005
 Protein intake (g/d)
  Low85613.511.001.00
  Normal65213.680.91 (0.80–1.04)0.93 (0.83–1.05)
  High157113.491.02 (0.93–1.16)0.99 (0.88–1.10)
  Missing12014.190.68 (0.54–0.86)*
  P trendc.444.921
 Fat intake (%)
  Low93114.011.001.00
  Normal95713.331.52 (1.40–1.66)**1.15 (0.97–1.36)
  High119113.281.62 (1.48–1.78)**1.02 (0.82–1.27)
  Missing12014.190.95 (0.74–1.23)
  P trendc<.001.542
 Carbohydrate intake (%)
  Low63813.181.001.00
  Normal126013.290.95 (0.87–1.04)1.01 (0.90–1.13)
  High118113.930.62 (0.57–0.68)**0.77 (0.63–0.94)*
  Missing12014.190.56 (0.45–0.71)**
  P trendc<.001.033
 Exercise (times/wk)
  ≤2205713.721.001.00
  3–773413.261.26 (1.13–1.41)**1.10 (0.99–1.23)
  ≥840013.161.38 (1.21–1.58)**1.06 (0.93–1.21)
  Missing813.391.14 (0.69–1.87)1.32 (0.69–2.53)
  P trendc<.001.176
  • Calculated with application of weights for the CHNS sample.

  • a From Kaplan-Meier survival probabilities.

  • b Adjusted for other covariates in the table.

  • c Calculated by using the median value of each category as a single ordinal variable in the Cox regression model.

  • * P < .05.

  • ** P < .01.