TABLE 2

Geometric mean levels of plasma SHBG (nmol/l) according to caffeinated coffee, decaffeinated coffee, tea, and caffeine consumption

Categories of intake*P for trend
0 cups/day≤1 cups/day2–3 cups/day≥4 cups/day
Caffeinated coffee, median (n)0 (185)1.0 (187)2.5 (212)4.5 (122)
    Match-adjusted model§23.1 (16.1–33.1)22.7 (15.8–32.7)24.7 (17.2–35.5)27.6 (19.1–39.9)0.002
    Categorical model23.0 (16.5–32.0)22.8 (16.3–31.8)23.6 (16.9–33.0)26.6 (18.9–37.4)0.01
    Spline model22.9 (16.5–31.9)22.7 (16.2–31.8)24.1 (17.2–33.6)26.0 (18.5–36.5)
Decaffeinated coffee, median (n)0 (401)0.4 (188)2.5 (84)4.5 (23)
    Match-adjusted model§24.5 (17.1–35.2)24.3 (16.8–35.4)25.2 (17.1–37.3)26.7 (17.4–40.9)0.44
    Categorical model23.7 (17.0–33.1)22.3 (15.8–31.3)23.2 (16.2–33.3)22.9 (15.5–33.9)0.75
    Spline model23.6 (16.9–32.9)23.5 (16.8–33.0)23.6 (16.5–33.6)23.5 (16.2–34.3)
Tea, median (n)0 (242)0.4 (351)2.5 (76)4.5 (28)
    Match-adjusted model§25.6 (17.9–36.7)23.6 (16.4–33.8)24.6 (16.9–35.8)21.6 (14.3–32.5)0.27
    Categorical model24.5 (17.6–34.1)23.3 (16.7–32.6)23.3 (16.5–32.8)21.4 (14.7–31.3)0.24
    Spline model24.4 (17.5–33.9)23.7 (17.0–33.1)22.5 (16.1–31.5)22.7 (15.9–32.3)
Caffeine category (mg/day)≤5051–250251–500>500
Caffeine intake (mg/day), median (n)13 (131)140 (209)366 (230)656 (123)
    Match-adjusted model§22.9 (15.8–33.0)22.5 (15.6–32.5)23.6 (16.4–34.0)26.9 (18.5–39.0)0.008
    Categorical model22.9 (16.5–32.0)23.2 (16.7–32.3)23.0 (16.5–32.1)26.6 (19.0–37.4)0.02
    Spline model23.0 (16.5–32.1)23.0 (16.6–32.0)23.7 (17.0–33.0)25.6 (18.3–35.8)
  • Data are geometric means (95% CI) unless otherwise indicated.

  • *P values for trend are based on median values in categories of the participants.

  • §Match-adjusted model: adjusted for age, race, duration of follow-up, and time of blood draw.

  • †Categorical model: adjusted for matching factors, smoking status, physical activity, alcohol use, total calories, and BMI.

  • ‡Spline model: estimates at category medians from quadratic spline regression models with one knot at the middle category boundaries, adjusted for covariates used in categorical model.