IJE Advance Access originally published online on March 11, 2004
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International Journal of Epidemiology, Volume 33, Number 3, pp. 534-541
IJE vol.33 no.3 © International Epidemiological Association 2004; all rights reserved.
Article |
Within-person variation in serum lipids: implications for clinical trials
1 University of Minnesota, School of Public Health, Division of Epidemiology, Minneapolis, MN, USA
2 Unilever Health Institute, Unilever Research & Development, Vlaardingen, The Netherlands
3 Institute for Nutrition Research, University of Oslo, Oslo, Norway
4 Wageningen University, Division of Human Nutrition and Epidemiology, Wageningen, The Netherlands, and Wageningen Centre for Food Sciences, Wageningen, The Netherlands
5 USDA Human Nutrition Research Center on Aging, Tufts University, Boston, MA, USA
Correspondence: Mark A Pereira, Division of Epidemiology, 1300 South Second Street, Ste. 300, Minneapolis, MN 55454, USA. E-mail: pereira{at}epi.umn.edu
Background Little is known about the degree to which behavioural, biological, and genetic traits contribute to within-person variation in serum cholesterol.
Materials and Methods The authors studied within-person variation in serum total and high density lipoprotein (HDL) cholesterol in 458 participants of 27 dietary intervention studies in Wageningen, The Netherlands, from 1976 to 1995.
Results For a median of 4 days between blood draws, the geometric mean of the within-person standard deviation was 0.13 mmol/l (
5 mg/dl, coefficient of variation = 3.0%) for total cholesterol and 0.04 mmol/l (1.5 mg/dl, coefficient of variation = 3.0%) for HDL cholesterol. In mixed-model linear regressions using within-person variance as the dependent variable and including lipid concentration and covariates listed below, within-person variance of both total cholesterol and HDL cholesterol was higher for greater number of days between blood draws and for self-selected diet rather than investigator-controlled diet. Within-person variance of total cholesterol only was higher for non-standardized versus standardized phlebotomy protocol and for female sex. The authors found evidence that the APOA4 –347 (12/22 genotype) and MTP –493 (11 genotype) polymorphisms may increase the within-person variation in total cholesterol.
Conclusion Under certain study design (self-selected diet, use of non-standardized phlebotomy protocol) or participant characteristics (female, certain polymorphisms) within-person lipid variance is increased and required sample size will be greater. These findings may have important implications for the time and cost of such interventions.
Keywords Cholesterol, data interpretation, diet, lipoproteins, periodicity, randomized controlled trials
Accepted 22 October 2003
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