Lowering Salt Intake in Chronic Kidney Disease: A Pilot Randomized Crossover Trial

ABSTRACT

Background:

It is well recognized that excess dietary salt intake plays a major role in the development of hypertension. Chronic Kidney Disease (CKD) is associated with excess salt and water retention (excess volume) which is associated with hypertension.

Hypotheses:

Hypothesis 1:

Dietary salt restriction will improve volume status in subjects with CKD stages 3-4 as assessed by Bioelectrical Impedance Analysis (BIA).

Hypothesis 2:

Dietary salt restriction will result in improved blood pressure control in patients with CKD stages 3-4.

Hypothesis 3:

Dietary salt restriction will decrease albuminuria in patients with CKD stages 3-4.

Patients and Trial Design: This randomized crossover pilot study is designed to assess the effect of salt restriction on volume status in patients with CKD stages 3 and 4.

Subjects will be randomized to a treatment order: (1) 4 weeks of salt restriction of \<85 mmol sodium per day, a 2 week washout period, and 4 weeks of usual salt diet, OR (2) 4 weeks of usual diet, 2 weeks washout, and 4 weeks of salt restriction. Patients will receive dietary counseling in person at each study visit and at weekly intervals by phone calls from study dieticians. At weeks 0, 4, 6 and 10, patients will undergo assessments for (i) physical examination with assessments for weight, blood pressure, pulse, anthropometrics and a standardized clinical assessment of volume status. (ii) volume status using bioelectrical impedance analysis (BIA) (iii) 24-hour urine testing for, albumin, creatinine and aldosterone Every 2 weeks throughout the study, a 24-hour urine sodium will be measured for compliance, and serum electrolytes will be assessed for safety.

Data Analysis: BIA measurements in the low salt group will be compared with the regular diet group using the standard linear model analysis for 2x2 crossover trials. Additionally, 24-hour ambulatory and static blood pressure and 24-hour urine aldosterone levels will be compared between the two groups.

Future Implications: A significant reduction in the degree of volume expansion (as assessed by BIA) and blood pressure as a result of a salt restricted diet would have implications for renal and cardiovascular protection and would warrant confirmation by a larger randomized trial.


Eligibility Criteria:
Inclusion Criteria:

Individuals eligible to participate in this study must meet all of the following criteria:

* Willing and able to provide written, signed informed consent after the nature of the study has been explained, and prior to any research-related procedures.
* Age ≥ 18 years and ≤ 85 years.
* Willing and able to comply with all study procedures.
* Patients with eGFR of 20 to 60 ml/min/173m2 by the abbreviated (4-variable) MDRD equation and a relatively stable clinical course.
* Sitting systolic blood pressure ≥ 100 mmHg prior to study entry (to exclude people at risk from hypotension from dietary salt reduction).

Exclusion Criteria:

Individuals who meet any of the following exclusion criteria will not be eligible to participate in the study:

* Recent acute illness (≤1 month). Minor ailments such as a recovered common cold or allergic rhinitis would not be considered as exclusion criteria but would be left to the site PI's discretion.
* Recent hospitalization (≤1 month) unless clearly for a minor elective procedure unlikely to interfere with BIA measurements. The final decision will be left to the site PI's discretion.
* Any psychological condition (including alcoholism) that could interfere with the patient's ability to comply with the study protocol.
* Subjects with baseline 24-hour urinary sodium excretion ≤100 mmol/day.
* Amputation of a limb other than fingers or toes.
* Pacemaker, defibrillator, implantable pump, artificial joint, pins, plates or other types of metal objects in the body (other than dental fillings).
* Coronary stents or metal suture material in the heart.
* Use of any investigational product or investigational medical device within 30 days prior to screening, or requirement for any investigational agent prior to completion of all scheduled study assessments.
* Weight over 300 pounds (limitation for examination table).
* Pregnancy or lactation.
* Patients with kidney diseases known to be associated with salt wasting (see above).
* Patients with atrial fibrillation as ambulatory blood pressure measurements may not be accurate in this setting.
* Any condition that, in the view of the PI, places the subject at high risk of poor treatment compliance or of not completing the study.