Associations between γ-glutamyltransferase (GGT) and biomarkers of atherosclerosis: the Multi-ethnic Study of Atherosclerosis (MESA).

OBJECTIVE: To evaluate associations between total serum γ-glutamyltransferase activity (GGT) and biomarkers of arteriosclerosis in the Multi-Ethnic Study of Atherosclerosis (MESA), including 6783 participants from four ethnic subgroups, i.e., White, Chinese, Black and Hispanic. METHODS: Associations between fasting total serum GGT activity and oxidized low-density lipoproteins (oxLDL), interleukin-6 (IL-6), C-reactive protein (CRP), and soluble intercellular adhesion molecule-1 (sICAM-1) were assessed. Following evaluation of linear trends between GGT and biomarkers of interest, multivariable linear regression models were serially adjusted for age, gender, site, ethnicity (M1); M1+lifestyle variables (M2); M2+traditional cardiovascular risk factors plus medications (M3); and M3+metabolic status (M4). Interactions were evaluated between GGT and age and ethnicity in all models. RESULTS: Linear trends were positive and significant between GGT and oxLDL, IL-6, CRP and sICAM-1 in crude models, and trends remained significant in all ethnic subgroups for CRP (p<0.0001) and sICAM-1 (p<0.001), and for IL-6 except in the Chinese. Trends between GGT and oxLDL were significant in the entire cohort and the White subgroup (p<0.0001), but not in other ethnic subgroups. Multivariable models demonstrated continuous strong, positive associations between GGT and CRP, IL-6 and sICAM-1. Associations between GGT and oxLDL were attenuated upon adjustment for LDL-C and other traditional risk factors. All models were attenuated with adjustment for metabolic status. No age interactions were evident. CONCLUSIONS: Our findings support the hypothesis that total serum GGT activity represents the impact of metabolic disease on vascular injury and atherosclerosis.

Estimating mean annual 25-hydroxyvitamin D concentrations from single measurements: the Multi-Ethnic Study of Atherosclerosis.

BACKGROUND: The seasonal variation in circulating 25-hydroxyvitamin D [25(OH)D] concentrations is large relative to mean values. Single measurements may misclassify annual exposure, which may lead to bias in research and complicate clinical decision making. OBJECTIVE: We aimed to develop and validate a model for adjusting a single measurement of a serum 25(OH)D concentration to the time of year it was measured. DESIGN: We measured serum 25(OH)D concentrations by using mass spectrometry in 6476 participants from the Multi-Ethnic Study of Atherosclerosis at baseline and again in a subset of 368 participants at a median of 17 mo later. We estimated a cosinor model to describe the seasonal variability in 25(OH)D concentrations and evaluated this model by using follow-up 25(OH)D measurements. RESULTS: The mean age of subjects was 62.1 y, 61.2% of participants were nonwhite, and 53.3% of participants were women. The cosinor model predicted follow-up 25(OH)D concentrations better than a single measurement [difference in root mean squared error (RMSE): 1.3 ng/mL; P< 0.001]. The cosinor model also better predicted the measured annual mean 25(OH)D concentration (difference in RMSE: 1.0 ng/mL; P< 0.001). Annual mean 25(OH)D concentrations estimated from the cosinor model reclassified 7.1% of participants with regard to 25(OH)D deficiency, which was defined as <20 ng/mL. An estimated annual mean 25(OH)D concentration <20 ng/mL was significantly associated with lower bone mineral density, whereas an untransformed 25(OH)D concentration <20 ng/mL was not. CONCLUSIONS: Cross-sectional data can be used to estimate subject-specific mean annual 25(OH)D concentrations from single values by using a cosinor model. The tool we developed by using this approach may assist research and clinical care of adults in North America by reducing the misclassification of 25(OH)D deficiency.