Table 1.

Characteristics of the premenopausal study population by quartiles of caffeine intake

<49 mg/d49–163 mg/d164–366 mg/d≥367 mg/d
N144144144145
Age at urine collection, y42.2 (4.0)42.9 (3.9)43.1 (3.9)43.4 (3.4)
Urinary creatinine, mg/L1,146 (589)1,209 (548)1,077 (590)1,094 (657)
Ovulatory cycle, %91908890
First-morning urine sample, %88867175
Sample collected 4–10 days before next menstrual period, %88878781
BMI at time of urine collection, kg/m224.7 (4.9)25.0 (5.1)25.4 (5.3)25.6 (6.0)
Height, inches65.1 (2.7)65.2 (2.5)65.1 (3.1)65.0 (2.3)
Caucasian, %97969995
Physical activity, MET-h/wk20.9 (18.6)21.3 (21.8)22.8 (20.9)20.7 (17.7)
Alcohol intake, g/d2.2 (5.5)3.5 (5.1)4.6 (6.2)5.3 (7.0)
Current smoker, %23612
Parous, %83818182
Age at first birth, y26.7 (4.3)26.6 (4.6)26.4 (4.8)27.3 (4.9)
Regular menstrual cycles, %96949497
Menstrual cycle length 26–31 days, %71666763
Coffee intake, cups/day0 (0)0.4 (0.4)1.6 (0.9)3.1 (1.1)
Decaffeinated coffee intake, cups/day0.4 (0.9)0.3 (0.7)0.4 (0.8)0.2 (0.6)
Tea intake, cups/day0.1 (0.1)0.5 (0.7)0.5 (1.0)0.4 (0.8)

NOTE: Values are means (SD) or percentages.