Short-Term Variations in Enterolactone in Serum, 24-Hour Urine, and Spot Urine and Relationship with Enterolactone Concentrations

Abstract

Enterolactone, a mammalian lignan, is produced by colonic microflora from precursors present in food plants. Because intake of vegetables, fruits, berries, or whole grains is related to the enterolactone concentration in blood (1)(2) and excretion in urine (3)(4), enterolactone may function as a biomarker of fiber-rich foods. Important characteristics for a biomarker include convenient, low-risk collection of samples; specific, reliable laboratory measurement; and a high ratio of between-person to total variability \[intraclass correlation (ICC)\] (5). In epidemiologic studies, analytes with a low ICC often show weak associations with any disease (6). The present study describes the short-term variation in enterolactone in serum, 24-h urine, and spot-urine enterolactone:creatinine ratio and the relationship between enterolactone concentrations in serum, 24-h urine, and spot urine. The study protocol was approved by the Ethics Committee on Epidemiology and Public Health in the hospital district of Helsinki and Uusimaa. Twenty volunteers (13 females and 7 males) were recruited among university students. Exclusion criteria included age <18 years, antibacterial treatment during the preceding 3 months, and any major illness or regular medication, except contraceptive pills. The average age of the participants was 22.2 years [95% confidence interval (CI), 21.4–22.9 years], and the average body mass index was 22.3 (20.9–23.6) kg/m2. Of the female participants, seven took oral contraceptives. The female participant who regularly took an antidepressant reported this only at the end of the study. One participant dropped out because of antibacterial treatment for a urinary tract infection. One spot-urine sample was missing for one female participant, who was thus excluded from that analysis. The samples were collected on 5 successive days (Monday to Friday) for within-week variation and on the following 3 Mondays for within-month variation. Participants began collecting their urine 24 h before serum and spot-urine samples were …