1.
Intraindividual variability of plasma antioxidants, markers of oxidative stress, C-reactive protein, cotinine, and other biomarkers.
Block, G, Dietrich, M, Norkus, E, Jensen, C, Benowitz, NL, Morrow, JD, Hudes, M, Packer, L
Epidemiology (Cambridge, Mass.). 2006;(4):404-12
Abstract
BACKGROUND Within-person variability in biomarkers results in random error that can attenuate estimates of association. Little information on such variability is available for a number of nutrition-related biomarkers. METHODS Blood samples obtained 2 to 4 weeks apart were analyzed for tocopherols, carotenoids, ascorbate, lipids, cotinine, C-reactive protein, and oxidative stress. Subjects (n = 206 men and women, mean age 45.4 years) were either smokers or passively exposed to smoke. We calculated intraindividual and interindividual variability and the number of measurements required to reduce attenuation. RESULTS For most biomarkers, 2 measurements would be required to limit the attenuation of correlation coefficients to no lower than 90% of the true correlation. If only one measurement were obtained, observed correlations would be approximately 80-88% of true correlations. For regression coefficients, 3 or 4 measures would be required. Exceptions were ascorbic acid and malondialdehyde, for which a single measure resulted in little attenuation. CONCLUSIONS For most serum markers, collection of 2 or more measurements per person is desirable to increase the ability to detect associations between biomarkers and health-related variables. If only one measure is possible, sample sizes should be planned to permit detection of associations that are likely to be observed, not the theoretical true associations. The results of this study, in which measurements were obtained 2 to 4 weeks apart, are relevant for epidemiologic research in which the exposure of interest is the subject's baseline or current status. It is likely that within-person variability would be greater over a period of months or years.
2.
Plasma C-reactive protein concentrations in active and passive smokers: influence of antioxidant supplementation.
Block, G, Jensen, C, Dietrich, M, Norkus, EP, Hudes, M, Packer, L
Journal of the American College of Nutrition. 2004;(2):141-7
Abstract
OBJECTIVE C-reactive protein (CRP) may directly affect the progression of atherosclerosis, and therefore, may be a target for reducing disease risk. The objective was to determine whether antioxidant supplementation reduces plasma CRP in active and passive smokers. DESIGN Randomized, double-blind, placebo-controlled, parallel group trial with 2 months exposure to study supplements. SETTING Berkeley and Oakland, California. SUBJECTS Healthy adult men and women, consuming <4 daily servings of fruits and vegetables, and who were actively or passively exposed to cigarette smoke. Analysis was limited to participants with detectable baseline CRP concentrations and no evidence of inflammation associated with acute illness at baseline or follow-up as reflected in CRP elevations (> or =10.0 mg/L). A total of 1393 individuals were screened, 216 randomized, 203 completed the study, and 160 were included in the analysis. INTERVENTIONS Participants were randomized to receive a placebo or vitamin C (515 mg/day) or antioxidant mixture (per day: 515 mg vitamin C, 371 mg alpha-tocopherol, 171 mg gamma-tocopherol, 252 mg mixed tocotrienols, and 95 mg alpha-lipoic acid). MEASURES OF OUTCOME Change in plasma CRP concentration. RESULTS Vitamin C supplementation yielded a 24.0% reduction (95% confidence interval, -38.9% to -5.5%, p = 0.036 compared to control) in plasma CRP, whereas the antioxidant mixture and placebo produced a nonsignificant 4.7% reduction (-23.9% to 19.3%) and 4.3% increase (-15.1% to 28.2%), respectively. Results were adjusted for baseline body mass index and CRP concentrations. CONCLUSIONS Plasma CRP itself may serve as a potential target for reducing the risk of atherosclerosis, and antioxidants, including vitamin C, should be investigated further to confirm their CRP-lowering and anti-inflammatory effects.