Obesity and the relationship between pre-hypertension and chronic kidney disease: can we really isolate the effect of pre-hypertension?

To the Editor: We read with interest the article by Yano et al.¹ entitled ‘Association between prehypertension and chronic kidney disease in the Japanese general population.’ We commend the authors on taking advantage of a large, unique data set to highlight this putative risk factor for chronic kidney disease (CKD); the study has important public health implications because of the pervasive and increasing presence of pre-hypertension with high-normal blood pressure (BP) (systolic BP between 130–139 mm Hg or diastolic BP between 85–90 mm Hg). However, the study provides only weak evidence that pre-hypertension with high-normal BP is an independent risk factor for CKD.

The authors found a statistically significant association between pre-hypertension with high-normal BP and CKD in men only. The association was small in size (odds ratio: 1.11 (95% confidence interval: 1.05–1.17), Table 3). It is unclear whether this small association is clinically significant; trivial effects may achieve statistical significance when sample sizes are large,² as in this study. Furthermore, the small association could be explained by residual confounding.³ The study collected data on height and weight, but not on waist circumference. Thus, the authors adjusted for obesity defined as body mass index ≥25cm², but this is an imperfect measure of obesity and may not reflect central obesity, which better predicts the adverse metabolic impact of visceral fat.⁴ Had the authors adjusted for central obesity, the relationship between prehypertension and CKD in men may have been completely null.