Use of self-reported height and weight biases the body mass index–mortality association

Abstract

Background Many large-scale epidemiologic data sources used to evaluate the body mass index (BMI: kg/m2) mortality association have relied on BMI derived from self-reported height and weight. Although measured BMI (BMIM) and self-reported BMI (BMISR) correlate highly, self-reports are systematically biased. Objective To rigorously examine how self-reporting bias influences the association between BMI and mortality rate. Subjects Samples representing the US non-institutionalized civilian population. Design and Methods National Health and Nutrition Examination Survey data (NHANES II: 1976-80; NHANES III: 1988-94) contain BMIM and BMISR. We applied Cox regression to estimate mortality hazard ratios (HRs) for BMIM and BMISR categories, respectively, and compared results. We similarly analyzed subgroups of ostensibly healthy never-smokers. Results Misclassification by BMISR among the underweight and obesity ranged from 30–40% despite high correlations between BMIM and BMISR (r>0.9). The reporting bias was moderately correlated with BMIM (r>0.35), but not BMISR (r<0.15). Analyses using BMISR failed to detect six of eight significant mortality HRs detected by BMIM. Significantly biased HRs were detected in the NHANES II full dataset (χ2 = 12.49; p = 0.01) and healthy subgroup (χ2 = 9.93; p = 0.04), but not in the NHANES III full dataset (χ2 = 5.63; p = 0.23) or healthy subgroup (χ2 = 1.52; p = 0.82). Conclusions BMISR should not be treated as interchangeable with BMIM in BMI-mortality analyses. Bias and inconsistency introduced by using BMISR in place of BMIM in BMI-mortality estimation and hypothesis tests may account for important discrepancies in published findings.

Body mass index and mortality in an ethnically diverse population: the Multiethnic Cohort Study

“…Although correlations between self-reported and measured values of these variables are usually strong, systematic errors according to sex, ethnicity, and overweight status have been reported [37–39]. One study in nationally representative U.S. samples assessed the BMI-mortality association using both self-reported and measured weight and height, and demonstrated that BMI based on self-reported values led to underestimation of the association for underweight and overestimation of the association for obesity [40]. Furthermore, long-term recall of weight at age 21 may be further error-prone.…”

Gene-Environment Interactions Controlling Energy and Glucose Homeostasis and the Developmental Origins of Obesity

“…Particularly pertinent to this review, maternal obesity is associated with gestational complications and adverse fetal and neonatal health outcomes (348,513). However, there remains a controversy as to the higher rate of mortality among the overweight and obese, particularly using selfreported BMI (244). Some report the so-called obesity paradox whereby the overall mortality was lower among those with T2DM and cardiovascular comorbidity and weight loss but not weight gain was associated with increased mortality and morbidity (124,125).…”

Coronary artery disease risk among obese metabolically healthy young men

“…Finally, we included only men in this study, thereby the generalization of our results to women was limited. The strengths of this study include the standardized and direct (rather than reported) measurements of height and weight (36), strict followup, and careful adjustment to other CAD risk factors.…”