Intraindividual Variability in Serum Micronutrients: Effects on Reliability of Estimated Parameters

• Published in: Epidemiology (Cambridge, Mass.) Mass.), 2009-01, Vol.20 (1), p.36-43
• Main Authors: Shvetsov, Yurii B., Hernandez, Brenda Y., Wong, Sze H., Wilkens, Lynne R., Franke, Adrian A., Goodman, Marc T.
• Format: Article
• Language: English
• Subjects: Adolescent; Adult; Aged; Attenuation coefficients; Biological and medical sciences; Blood; Blood plasma; Carotenoids; Correlation coefficients; Epidemiology; Female; General aspects; Hawaii; Humans; Medical sciences; METHODS; Micronutrients; Micronutrients - blood; Middle Aged; Miscellaneous; Models, Statistical; Nutritional Status; Original; Public health. Hygiene; Public health. Hygiene-occupational medicine; Regression coefficients; Reproducibility of Results; Statistical variance; Tocopherols; Transcriptional regulatory elements; Young Adult
• ISSN: 1044-3983; 1531-5487
• DOI: 10.1097/EDE.0b013e318187865e

Background: Although serum measures of micronutrients are more specific than questionnaires in quantifying nutritional status, the reliability of serum measures depends on between- and within-person variability of circulating micronutrient levels. The extent to which multiple samples per person might improve reliability is useful information for planning studies and interpreting results. Methods: We analyzed levels of 25 micronutrients in serum samples taken from 381 Hawaii women at 4-month intervals. For all subjects and for subjects at the low and high end of the micronutrient distributions, we calculated inter- and intraindividual variability, reliability coefficients, and the number of measurements required to limit attenuation in estimated parameters (ie, to keep estimates close to their true values). Results: For 18 of the 25 micronutrients, a single measurement provided an estimate within 20% of the true value. For regression coefficients, 2 measurements were needed to limit attenuation to no more than 20% for nearly half of the micronutrients. To achieve no more than 10% attenuation, the number of measurements required ranged from 2 to 10 for correlation and from 3 to 20 for regression coefficients. To achieve no more than 5% attenuation, the corresponding ranges were 3 to 21 for correlation and 6 to 42 regression coefficients. In general, more measurements were required for adequate characterization of subjects with relatively high levels of micronutrients than for subjects with lower levels. Conclusions: Our analysis suggests that 2 or 3 blood measurements are enough to limit attenuation of regression coefficients within 20% of the true value for most carotenoids and tocopherols. For 10% attenuation or less, 4 or more micronutrient measurements may be needed.