Within-person reproducibility of red blood cell mercury over a 10- to 15-year period among women in the Nurses’ Health Study II

Abstract

Background Most epidemiologic studies of methylmercury (MeHg) health effects rely on a single measurement of a MeHg biomarker to assess long-term exposures. Long-term reproducibility data are, therefore, needed to assess the reliability of a single measure to reflect long-term exposures. In this study we assessed within-person reproducibility of red blood cell (RBC) mercury (Hg), a marker of methyl-mercury, over 10–15-years in a sample of 57 women. Methods Fifty-seven women from the Nurses’ Health Study II provided two blood samples 10–15-years apart (median:12 years), which were analyzed for mercury levels in the red blood cells (B-Hg*). To characterize within-person reproducibility we estimated correlation and intraclass correlation coefficients (r and ICC) across the two samples. Further, we compared different prediction models, including variables on fish and seafood consumption, for B-Hg* at the first sample using leave-one-out cross-validation to assess predictive ability. Results Overall, we observed strong correlations over 10–15 years (r=0.69), as well as a high ICC (0.67; 95%CI: 0.49, 0.79). Fish and seafood consumption reported concurrently with the first B-Hg* sample accounted for 26.8% of the variability in that B-Hg*, giving a correlation of r=0.52. Conclusions Despite decreasing B-Hg* levels over time, we observed strong correlations and high ICC estimates across B-Hg* measured 10–15 years apart, suggesting good relative within-person stability over time. Our results indicate that a single measurement of B-Hg* likely is adequate to represent long-term exposures.

Tampon use, environmental chemicals and oxidative stress in the BioCycle study

“…Information on all potential confounders was obtained from the baseline questionnaires. Additionally, models for mercury exposure were adjusted for fish consumption because exposure might reflect increased fish and seafood consumption [27], and could be related to tampon use through socioeconomic status (SES). For this analysis, fish consumption was assessed as the sum (continuous) of four variables from a food frequency questionnaire (FFQ) administered at baseline: 1) fried fish and shellfish and fish sandwich, 2) shellfish (not fried), 3) white fish such as sole, halibut, snapper and cod, 4) and dark fish such as salmon, mackerel and bluefish.…”