Nocturnal Blood Pressure Dipping in Normotensive Adults: Effect of Dietary Sodium and Sex

Abstract

Normal nocturnal blood pressure (BP) dipping is arbitrarily defined as a decrease in mean daytime to mean nighttime BP by 10% to 20%. Individuals that have impaired nocturnal BP dipping (i.e., <10%) have an increased risk of cerebrovascular and cardiovascular diseases. Excess sodium consumption is associated with increased cardiovascular disease risks and no studies have examined nocturnal BP dipping under a controlled sodium diet.PURPOSETo assess nocturnal BP dipping during low (LS) and high sodium (HS) diets in men and women. We hypothesized that a HS diet would impair nocturnal BP dipping, and men would have a greater impairment than women.METHODSEighty‐seven healthy normotensive men (n = 41; age: 35 ± 2 years) and women (n = 46; age: 40 ± 2 years) participated in a controlled feeding study where LS (20 mmol Na+/day) and HS (300 mmol Na+/day) diets were provided for 7 days each in random order. Subjects wore a 24‐hour ambulatory BP monitor, and we collected a 24‐hour urine sample and fasted blood sample on the final day of each diet. Nocturnal BP dipping was calculated as: ((mean daytime BP – mean nighttime BP)/mean daytime pressure)*100.RESULTSAs expected, there was a significant increase in urinary sodium excretion during the HS diet (women: LS = 26.0 ± 2.1 vs. HS = 238.4 ± 14.1 mmol/24hr; men: LS = 31.5 ± 4.4 vs. HS = 234.4 ± 13.3 mmol/24hr; p < 0.01) and serum sodium (women: LS = 137.7 ± 0.3 vs. HS = 139.7 ± 0.2 mmol/L; men: LS 137.9 ± 0.4 vs. HS = 139.8 ± 0.3; p < 0.05) with no differences observed between the sexes. Nocturnal BP dipping was not different between the diets (women: LS = 10 ± 1% vs. HS = 10 ± 1% mmHg; men: LS = 9 ± 1% vs. HS = 10 ± 1% mmHg; p > 0.05) with no differences observed between the sexes.CONCLUSIONOur findings suggest that increased dietary sodium does not influence nocturnal BP dipping responses in normotensive men and women.Support or Funding InformationNIH Grant R01 HL104106