Establishing Biomarkers of Oxidative Stress: The Measurement of Hydrogen Peroxide in Human Urine

Hydrogen peroxide (H2O2) can be detected in freshly-voided human urine from healthy subjects and has been proposed as a “biomarker” of oxidative stress. This paper summarizes our studies to examine the extent to which urinary H2O2 measurement fulfils the criteria for the “ideal biomarker”. Levels of H2O2, standardised for creatinine, varied widely between subjects. In most subjects, levels also varied considerably when measurements were made at different times and on different days. A reproducible increase in urinary H2O2 was detected in all subjects examined after drinking coffee, a beverage rich in H2O2. By contrast, green tea decreased urinary H2O2 levels. We conclude that the H2O2 in coffee is not excreted into urine. Instead, hydroxyhydroquinone from coffee is absorbed, excreted and oxidises in urine to produce H2O2. No other confounders of urinary H2O2 have been identified to date. Work is underway to compare H2O2 levels with variations in other biomarkers of oxidative damage, to test the possibility that there are daily or other periodic variations in oxidative damage rates.