Timing of Sodium Intake and Nocturnal Sodium Excretion and Blood Pressure in Obese African Americans

Experimental data have shown that timing of sodium intake impacts diurnal patterns of sodium excretion. The purpose of this study is to test the hypothesis that the time of day for salt intake impacts (1) blood pressure rhythms and urinary sodium excretion and (2) circadian timing of factors responsible for blood pressure regulation and cardiometabolic health in obese individuals. These studies will address two aims. The first aim will test the hypothesis that limiting high salt intake prior to sleep increases day-night differences in blood pressure, improves timing of urinary sodium excretion, and improves metabolic risk factors. The second aim will test the hypothesis that limiting high salt intake prior to sleep preferentially improves rhythmicity in peripheral vs. central circadian clock factors linked to renal sodium handling. The proposed hypothesis-driven studies will determine how timing of sodium intake affects diurnal blood pressure and circadian timing of factors responsible for blood pressure control and metabolic health, with the ultimate goal of identifying novel strategies to treat nocturnal hypertension and metabolic disease in obesity.

Inclusion Criteria: * obese (BMI 30-50 kg/m2) * 25-45 years of age Exclusion Criteria: * evidence of kidney disease (eGFR \< 60 ml/min/1.73m2 or abnormal urinalysis) * elevated BP (\>150/90 mmHg \[measured at screening in duplicate after 10min lying recumbent\]) * elevated fasting glucose (\>126 g/dL on screening labs) * severe anemia (hemoglobin \< 8 g/dL for women or \< 9 g/dL for men) * significant psychiatric illness (as assessed by a validated screening form) * past or present drug or alcohol abuse (drug screen) * taking 2 or more BP medications or supplements on a regular basis * alcohol intake more than 2 drinks/day * pregnancy * women taking hormone replacement therapy, or post-menopausal women; * shift worker * sleep disorders (such as sleep apnea assessed by Apnea Link) * major chronic disease (e.g., diabetes, lymphocyte disorders) * history of smoking or use of tobacco products within the past year * use of sleep medications, hypnotics, stimulants, or anti-depressants