Dietary sodium and blood pressure in treatment-resistant hypertension
Elevated blood pressure (BP) is an important contributor to the risk of developing cardiovascular disease (CVD). One subgroup of people is defined by a lack of BP control despite three antihypertensive medications (one diuretic), all at optimal dosing. Referred to as treatment-resistant hypertension (TRH), this condition presents a particular CVD risk.
Lifestyle modification, including the restriction of dietary sodium, is important in the treatment of people with TRH. However, many sodium-restricted diets, which aim to lower intake to 6 g/day, are not easy to follow. The present study aimed, therefore, to see if self-performed dietary sodium restriction could be implemented in people with TRH in the real-world setting, and to evaluate the effect of this intervention on BP.
Additionally, it explored whether nocturnal and 24-hour BP changes in response to sodium restriction could be explained by mechanisms involving nitric oxide (NOx), water retention, renal function or renal handling of sodium. Lastly, erythrocyte sodium sensitivity (ESS) was investigated as a possible predictor for the effect of sodium restriction on BP.
This interventional study, conducted in Denmark, included 15 adults with TRH (11 males; mean age 59 years) with eGFR >45 mL/min/1.73 m² and 24-h BP ≥130/80 mmHg. Participants followed their usual diet for 2 weeks before switching to 2 weeks on a self-performed sodium-restricted diet, during which sodium-free bread was provided. At the end of each period, 24-h BP and 24-h urine collections were performed, blood samples were drawn and bio-impedance was measured.
Following the sodium-restriction intervention, nocturnal and 24-h systolic BP decreased significantly (–8 and –10 mmHg, respectively; P<0.05). Urinary sodium excretion decreased significantly from 186 to 91 mmol (corresponding to ~5.5 g of salt), with 14/15 participants showing a reduction.
Plasma NOx increased following the intervention, with the change correlating to 24-h SBP reduction. Brain natriuretic peptide (BNP) and extracellular water content also increased significantly. ESS was not related to changes in BP and could not, therefore, be used to predict the effect of sodium restriction.
Despite acknowledging some study limitations, such as its small size, the authors conclude that it demonstrates that self-performed dietary sodium restriction can be implemented safely in people with TRH to reduce BP. NOx synthesis may be involved in the BP-lowering effect, along with reduced body water content.
The full study can be read here.
