Salt Sensitivity Evaluation Via N-of-1 Trials (SENSE-Salt)

Study Title: Determining the Presence of Salt Sensitivity in Individuals With Elevated Blood Pressure Through Dietary Salt Interventions: A Series of N-of-1 Trials Objective: 1. Primary Objective: To assess whether there are differences in blood pressure responses between salt-sensitive and salt-resistant individuals. 2. Exploratory Objectives: To explore the effects of different sodium-content diets on individual pulse, sleep, and mood; to evaluate whether a low-sodium diet increases the incidence of hypotension; and to identify metabolic differences associated with salt sensitivity. Study Design: This study will utilize a two-phase N-of-1 randomized controlled trial design. It consists of the following phases: 1. Salt Sensitivity Screening: Participants will undergo a 2-week dietary intervention (1 week of high-sodium diet: 200 mmol/day; 1 week of low-sodium diet: 85 mmol/day). Salt sensitivity will be determined by comparing changes in mean arterial pressure (MAP) between the high-sodium and low-sodium periods (△MAP). Individuals with △MAP ≥5 mmHg and in the upper 1/6 of the population will be classified as salt-sensitive (SS), while those with △MAP \<5 mmHg and in the lower 1/6 will be classified as salt-resistant (SR). 2. N-of-1 Trial: The identified salt-sensitive and salt-resistant individuals will undergo a 6-week N-of-1 trial, consisting of three cycles. Each cycle will last 2 weeks (1 week of high-sodium diet and 1 week of low-sodium diet). This design aims to assess individual blood pressure responses to changes in sodium intake. Sample Size: A total of 72 participants will be recruited for the salt sensitivity screening, with an expected 24 participants proceeding to the N-of-1 trial. Study Population: Healthy individuals aged 20-65 years, not on antihypertensive medication or with a stable regimen for at least 3 months, with systolic blood pressure between 110-159 mmHg and diastolic blood pressure between 70-99 mmHg, who are able to eat at the research center. Primary Outcome: Reproducibility of salt sensitivity response classification. Secondary Outcomes:Changes in mean arterial pressure, systolic and diastolic blood pressure; exploratory outcomes such as sleep, mood, gut microbiome, and metabolomics; and safety outcomes including hypotension and hyponatremia.