Figure 2.

Cubic spline graph of the adjusted HR (represented by solid line) and 95% CI (represented by the dotted lines) for the association between menstrual and reproductive factors and lung cancer risk. (A) Age at menarche, reference: 14 years old; (B) age at first live birth, reference: 25 years old; (C) duration of breastfeeding, reference: 12 months; (D) age at menopause, reference: 50 years old; (E) reproductive period, reference: 35 years; Knots: 5th, 50th, 95th of the distribution. Analyses are adjusted for age at enrollment (continuous), education (low, medium, or high), BMI (underweight, normal, overweight or obese), smoking status (current, former or never-smoker), exposures to environmental tobacco smoke (yes or no), exposure to cooking smoke (none, little, some, or much), occupational exposures (yes or no), history of chronic respiratory disease (yes or no) and family history of lung cancer (yes or no).