title: Caffeinated beverage intake and reproductive hormones among premenopausal women in the BioCycle Study.
abstract: BACKGROUND
  Caffeinated beverages are widely consumed among women of reproductive age, but their association with reproductive hormones, and whether race modifies any such associations, is not well understood.
  
  
  OBJECTIVE
  We assessed the relation between caffeine and caffeinated beverage intake and reproductive hormones in healthy premenopausal women and evaluated the potential effect modification by race.
  
  
  METHODS
  Participants (n = 259) were followed for up to 2 menstrual cycles and provided fasting blood specimens for hormonal assessment at up to 8 visits per cycle and four 24-h dietary recalls per cycle. Weighted linear mixed models and nonlinear mixed models with harmonic terms were used to estimate associations between caffeine and hormone concentrations, adjusted for age, adiposity, physical activity, energy and alcohol intakes, and perceived stress. On the basis of a priori assumptions, an interaction between race and caffeine was tested, and stratified results are presented.
  
  
  RESULTS
  Caffeine intake ≥200 mg/d was inversely associated with free estradiol concentrations among white women (β = -0.15; 95% CI: -0.26, -0.05) and positively associated among Asian women (β = 0.61; 95% CI: 0.31, 0.92). Caffeinated soda intake and green tea intake ≥1 cup/d (1 cup = 240 mL) were positively associated with free estradiol concentrations among all races: β = 0.14 (95% CI: 0.06, 0.22) and β = 0.26 (95% CI: 0.07, 0.45), respectively.
  
  
  CONCLUSIONS
  Moderate consumption of caffeine was associated with reduced estradiol concentrations among white women, whereas caffeinated soda and green tea intakes were associated with increased estradiol concentrations among all races. Further research is warranted on the association between caffeine and caffeinated beverages and reproductive hormones and whether these relations differ by race.
authors.affiliation: Division of Epidemiology, Statistics, and Prevention Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, MD, USA.
authors.forename: Karen C
authors.initials: KC
authors.lastname: Schliep
authors.forename: Enrique F
authors.initials: EF
authors.lastname: Schisterman
authors.forename: Sunni L
authors.initials: SL
authors.lastname: Mumford
authors.forename: Anna Z
authors.initials: AZ
authors.lastname: Pollack
authors.forename: Cuilin
authors.initials: C
authors.lastname: Zhang
authors.forename: Aijun
authors.initials: A
authors.lastname: Ye
authors.forename: Joseph B
authors.initials: JB
authors.lastname: Stanford
authors.forename: Ahmad O
authors.initials: AO
authors.lastname: Hammoud
authors.forename: Christina A
authors.initials: CA
authors.lastname: Porucznik
authors.forename: Jean
authors.initials: J
authors.lastname: Wactawski-Wende
mesh_terms: D000293:Adolescent; D000328:Adult; D001628:Beverages; D002110:Caffeine / Q000494:pharmacology*; D028241:Camellia sinensis / Q000737:chemistry; D004032:Diet; D004958:Estradiol / Q000097:blood*; D005260:Female; D006801:Humans; D015233:Models, Statistical; D010936:Plant Extracts / Q000494:pharmacology*; D017697:Premenopause; D044469:Racial Groups; D055815:Young Adult
chemical_list: D010936:Plant Extracts; D002110:Caffeine; D004958:Estradiol