Effects of dietary sodium on blood pressure in IDDM patients with nephropathy

Abstract

The objectives of the study were to assess the effects of moderate sodium restriction on blood pressure in insulin-dependent diabetic (IDDM) patients with nephropathy and high normal or mildly hypertensive blood pressure (primary objective), and to document possible associated changes of exchangeable body sodium, body volumes, components of the renin-angiotensin-aldosterone system, atrial natriuretic peptide, and catecholamines (secondary objective). Sixteen patients with untreated systolic blood pressure > or = 140 < 160 mmHg and/or diastolic blood pressure > or = 85 < 100 mmHg were included in a double-blind, randomized, placebo-controlled trial. After a 4-week run-in period on their usual diet and a 2-week dietary training period to reduce sodium intake to about 90 mmol/day, eight patients received 100 mmol/day sodium supplement (group 2) and eight patients a matching placebo (group 1) for 4 weeks while continuing on the reduced-sodium diet. Patients were examined at weekly intervals. Main response variables were mean values of supine and sitting systolic and diastolic blood pressure as measured in the clinic and by the patients at home. The differences in blood pressure between the beginning and the end of the blinded 4-week study period were calculated and the differences in changes between the two patient groups were regarded as the main outcome parameters. During the blinded 4-week study period, average urinary sodium excretion was 92 +/- 33 (mean +/- SD) mmol/day in group 1 and 199 +/- 52 mmol/day in group 2 (p = 0.0002). The differences in blood pressure changes between the two patient groups were 3.9(-1.2 to 9) mmHg [mean (95% confidence intervals)] for systolic home blood pressure, 0.9(-3.7 to 5.5) mmHg for diastolic home blood pressure, 4.9(-3.3 to 13.1) mmHg for clinic systolic blood pressure and 5.3(1 to 9.7 mmHg, p = 0.02) for clinic diastolic blood pressure. Combining all patients, there were relevant associations between changes of urinary sodium excretion and blood volume (Spearman correlation coefficient r = 0.57), blood pressure and angiotensin II (diastolic: r = -0.7; systolic: r = -0.48), and exchangeable body sodium and renin activity (r = -0.5). In conclusion, in this study of IDDM patients with nephropathy and high normal or mildly hypertensive blood pressure, a difference in sodium intake of about 100 mmol/day for a period of 4 weeks led to a slight reduction of clinic diastolic blood pressure. Studies including larger numbers of patients with various stages of nephropathy and hypertension are needed to definitely clarify the effects of sodium restriction in IDDM.

Salt Restriction Reduces Hyperfiltration, Renal Enlargement, and Albuminuria in Experimental Diabetes

“…Salt restriction reduced the volume of distribution of the HTc]DTPA, which is a marker of the extracellular volume status. This is supported by a recent study in human diabetes that demonstrated a significant correlation between urinary sodium excretion and plasma volume (38). Therefore, salt restriction in experimental diabetes may result in a decrease in the extracellular volume and in stimulation of the RAS, leading to a fall in atrial natriuretic peptide (ANP) release from the heart (39,40).…”

Association of dietary sodium intake with atherogenesis in experimental diabetes and with cardiovascular disease in patients with Type 1 diabetes

“…It has been argued that the clear benefits of additional BP lowering demands a low-sodium diet in all patients with diabetes [5]. At the same time, RAAS activation is clearly increased with sodium restriction in diabetic patients [33], and the wide clinical utility and effects of drugs that block the RAAS [3] stand as testament to the importance of this pathway in diabetes, beyond its actions on BP regulation. In addition, we have previously been unable to observe any association between sodium intake and BP indices in patients with either Type 1 or Type 2 diabetes after adjusting for age and gender, with or without antihypertensive treatment [6,7].…”

Effects of Sodium Restriction on Blood Pressure, Renin, Aldosterone, Catecholamines, Cholesterols, and Triglyceride

“…However, it is too early to draw final conclusions because of lack of long-term (Ͼ4 weeks) studies with a moderate reduction in sodium intake (about 100 mmol/24 h). Blood lipid levels were only investigated in 2 to 5 long-term studies with a mean sodium reduction of 75 mmol/24 h. 26,43,56,57,87 The evidence from these was not statistically significant. The effect on the lipid profile may be secondary to a shift in fluid balance such as hemoconcentration; in the present study this premise is supported by a significant body weight reduction of about 1 kg in the sodium-reduced group, probably reflecting a decrease in total body water.…”