Impaired pressure natriuresis in obese youths

Objective: To compare the response and recovery of blood pressure (BP) and sodium excretion (U_NaV) in response to a behavioral stressor in overweight/obese and lean adolescents. Research Methods and Procedures: Twenty-five lean (12% to 20% body fat) and 59 overweight/obese (>25% body fat) normotensive adolescents were provided all meals for 3 days (average sodium intake, 4000 ± 200 mg/d), before performing the stressor on the third day. There was a 2-hour pre-stress rest, followed by a 1-hour stress (involving a video game task), and a 2-hour recovery. Percentage of body fat was obtained from DXA. U_NaV was measured hourly, whereas systolic BP and diastolic BP measurements were obtained at 15-minute intervals, and averaged for each 1-hour period. Results: There was no significant difference between the lean and overweight/obese group for the response of systolic BP and diastolic BP (group by time interaction, p = 0.60 and p = 0.64, respectively). However, the lean group had a significantly greater increase in U_NaV in response to the stressor compared with the overweight/obese group (p = 0.02). U_NaV remained elevated compared with baseline in both groups at the 1-hour (p < 0.0001) and 2-hour (p ≤ 0.0001) post-time points. Furthermore, there was a tendency for a larger number of sodium retainers in the overweight/obese group compared with the lean group (39.0% vs. 20.0%; χ² = 2.85, df = 1, p = 0.09). Discussion: This study provided evidence that sodium regulation was impaired during a behavioral stress in overweight/obese individuals compared with lean individuals.