Caffeine consumption and menstrual function

The relation between caffeine intake and menstrual function was examined in 403 healthy premenopausal women who belonged to Kaiser Permanente Medical Care Program in 1990-1991. A telephone interview collected information abou t caffeinated beverage intake as well as other lifestyle, demographic, occu pational, and environmental factors. Subjects collected daily urine samples and completed a daily diary for an average of five menstrual cycles. Metab olites of estrogen and progesterone were measured in the urine, each cycle was characterized as anovulatory or ovulatory, and a probable day of ovulat ion was selected when appropriate. Logistic regression and repeated measure s analyses were performed on menstrual parameters. Women whose caffeine con sumption was heavy (> 300 mg of caffeine per day) had less than a third of the risk for long menses (greater than or equal to 8 days) compared with wo men who did not consume caffeine (adjusted odds ratio = 0.30, 95% confidenc e interval 0.14-0.66). Those whose caffeine consumption was heavy also had a doubled risk for short cycle length (less than or equal to 24 days) (adju sted odds ratio = 2.00, 95% confidence interval 0.98-4.06); this associatio n was also evident in those whose caffeine consumption was heavy who did no t smoke (adjusted odds ratio = 2.11, 95% confidence interval 1.03-4.33). Ca ffeine intake was not strongly related to an increased risk for anovulation , short luteal phase (less than or equal to 10 days), long follicular phase (greater than or equal to 24 days), long cycle (greater than or equal to 3 6 days), or measures of within-woman cycle variability.