Temporal variability of isoflavone and lignan concentrations in spot urine samples in 50 North Carolina adults over a six-week period (ICPH2019)
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Objectives: Urine phytoestrogens are often measured in epidemiological studies as proximal biomarkers of dietary intake and evaluated as risk factors in various diseases and conditions. The design and interpretation of such studies requires an understanding of the temporal variability of urine measurements. The US EPA’s Pilot Study to Estimate Human Exposures to Pyrethroids Using an Exposure Reconstruction Approach (Ex-R Study) investigated the exposure of 50 adults (19–50 years old) in North Carolina, USA to pyrethroid insecticides over a 6-week period in 2009–2011. The Ex-R Study was designed to assess the temporal variability of pesticide exposure biomarkers, and its urine sampling schedule is suitable for studying repeat measures performed on any urinary compound. Our objective was to describe the temporal concentration variability of six urine phytoestrogens over periods ranging from 24 h to 6 weeks by use of the Ex-R Study.
Methods: We measured spot urine concentrations of four phytoestrogenic isoflavones (daidzein [DAZ], genistein [GNS], equol [EQU], O-desmethylangolensin [DMA]) and two enterolignans (enterolactone [ETL], enterodiol [ETD]) by use of LC-MS/MS in 2292 surplus samples from the Ex-R Study. Spot urine samples collected over the 6-week study were classified as bedtime voids, first-morning voids, or individual voids obtained over a continuous 24-h period. We reported results by concentration, specific gravity (SG) and creatinine (CR) adjusted concentrations, and excretion rate. In addition to general descriptive statistics, we calculated between-person (bR ̂0.95) and within-person (wR ̂0.95) 95% fold range estimates, and intra-class correlation coefficients (ICC). We used ICCs to determine whether a single spot urine sample was sufficient to satisfy a specified degree of reliability (ICC ≥0.80) over a given timeframe.
Results: We detected all target analytes in >99% of study samples with the exception of DMA (96%) (LODs: 0.05–0.1 ng/mL). We found that bR ̂0.95 exceeded wR ̂0.95 in all concentration calculation and timeframe combinations for ETL and most combinations for DMA and ETD, with mixed results for other analytes. We observed that wR ̂0.95 decreased for all analytes in the 24-h period voids when concentration adjustments were used, and that SG- and CR-normalization decreased wR ̂0.95 for bedtime and first morning voids in most cases. Adjusting for SG, CR and excretion rate had a mixed impact on bR ̂0.95. We found across all analytes that ICCs were generally highest for individual voids when calculated over a 24-h period (0.60–0.96) and lowest for bedtime and first morning voids when calculated over the entire 6-week study (0.23–0.70). ICCs for individual voids over a given 24-h period were highest for SG and CR normalized concentrations of DMA and ETL (0.90–0.96), and were generally ≥0.80 for the remaining analytes. The highest ICCs we observed when calculated across the entire 6-week study were for excretion rate and SG- and CR-normalized ETL concentrations in the individual 24-h period voids (0.71–0.75).
Conclusion: Based upon the temporal variability we observed in the Ex-R Study, it may be possible to reliably estimate (ICC ≥0.80) urine concentrations of DAZ, DMA, EQU, ETD, ETL and DAZ over a given 24-h period by use of a single spot urine sample and SG- or CR adjustment, with more samples needed for longer timeframes.