Does waist circumference uncorrelated with BMI add valuable information?
- 1Population Health and Optimal Health Practices Research Unit, CHU de Québec Research Centre, Québec, Québec, Canada
- 2Department of Social and Preventive Medicine, Faculty of Medicine, Laval University, Québec, Québec, Canada
- Correspondence to Dr Michel Lucas, Population Health and Optimal Health Practices Research Unit, CHU de Québec Research Centre, 2875 Laurier Blvd., Delta 2 Building, Office 600, Québec, Québec, Canada G1V 2M2;
- Received 10 February 2014
- Revised 13 May 2014
- Accepted 21 May 2014
- Published Online First 10 June 2014
Background Estimation of relative contribution of Body Mass Index (BMI) and waist circumference (WC) on health outcomes requires a regression model that includes both obesity metrics. But, multicollinearity could yield biased estimates.
Methods To address the multicollinearity issue between BMI and WC, we used the residual model approach. The standard WC (Y-axis) was regressed on the BMI (X-axis) to obtain residual WC. Data from two adult population surveys (Nunavik Inuit and James Bay Cree) were analysed to evaluate relative effect of BMI and WC on four cardiometabolic risk factors: insulin, triglycerides, systolic blood pressure and high-density lipoprotein levels.
Results In multivariate models, standard WC and BMI were significantly associated with cardiometabolic outcomes. Residual WC was not linked with any outcomes. The BMI effect was weakened by including standard WC in the model, but its effect remained unchanged if residual WC was considered.
Conclusions The strong correlation between standard WC and BMI does not allow assessment of their relative contributions to health in the same model without a risk of making erroneous estimations. By contrast with BMI, fat distribution (residual WC) does not add valuable information to a model that already contains overall adiposity (BMI) in Inuit and Cree.