Introduction: The association between the sodium-to-potassium ratio (NK ratio) and blood pressure was well recognized in adults and children. However, the interaction between NK ratio and obesity for blood pressure was unclear.
Hypothesis: We hypothesized that the association between NK ratio and blood pressure was varied with the degree of obesity in children.
Methods: A total 2818 children aged between 6-18 yrs old was analyzed from National Nutrition and Health Survey during 2010-2012. First-morning urine was collected for measuring urinary sodium and potassium. The urinary NK ratio was classified low (<25th [NK=2.83], n=702), middle (25th ~ 75th[2.83-6.36], n=1411) and high (≥75th[6.37],n=705) groups. Overweight or obesity (n=443,15.7%) was classified by the age and sex specific criteria, proposal by the health promotion administration (Taiwan). Average continuous twice blood pressure measurements with seating position was used. General linear and logistic regressions were used to evaluate the association between urinary sodium-to-potassium ratio and blood pressure.
Results: Urinary sodium-to-potassium ratio was positively associated with systolic blood pressure (BP) (r=0.115,P=0.015) and mean blood pressure (r=0.097, P=0.040) in overweight children, but not in those without overweight (r=-0.030 and p=0.140 for SBP; r=-0.016, p=0.441 for mean BP). The age and sex-adjusted means of systolic BP were 109.6, 108.1, and 106.6 mmHg for high, middle and low NK ratio, respectively (p for trend= 0.039) in overweight children and were 100.4, 100.0 and 100.5 mmHg for high, middle and low NK ratio, respectively (p for trend= 0.814) in the children without overweight (p for interaction= 0.040). Furthermore, the odds ratio (95% confidence intervals) of elevated systolic BP (≥110 mm Hg, n=579) was 5.89 (3.80-9.13) for overweight plus a high NK ratio, 5.50 (3.95-7.67) for overweight plus a middle NK ratio and 3.16 (1.93-5.16) for overweight plus low NK ratio, compared to those without overweight, in the multivariable model with controlling aging and sex.
Conclusions: Obesity enhances the association between urinary sodium-to-potassium ratio and blood pressure, and sodium intake should be strictly controlled in the overweight children.