Blood Pressure, Diet and the Progression of Nephropathy in Patients with Type 1 Diabetes and Hypertension

To examine the relationships between the normal dietary intakes of protein and phosphate, blood pressure, and the progression of diabetic nephropathy, we prospectively studied 20 Type 1 diabetic subjects of mean age 43 ± 10 years (SD) with early nephropathy (mean serum creatinine 115 ± 43 μmol l ‐1 ) over 1 year. Three‐monthly measurements of blood pressure, glycaemic control, and normal dietary intake (3‐day weighed food records) and 6‐monthly measurements of glomerular filtration rate (using a single injection of chromium 51 ‐EDTA) were made. GFR changed at a median rate of ‐0.89 ml min ‐1 1.73 m ‐2 month ‐1 (range + 0.85 to ‐2.55 ml min ‐1 1.73 m ‐2 month ‐1 ). Mean dietary protein intake (1.22 g kg ‐1 ; range 0.78 to 1.55 g kg ‐1 ) and phosphate intake (21.5 mg kg ‐1 ; range 14.1 to 30.4 mg kg ‐1 ) were not significantly related to the rate of change in GFR. Only mean systolic blood pressure was significantly related to change in GFR, and accounted for 45 % of the variability in GFR decline in the 18 subjects who completed the study ( r = 0.67; R 2 = 0.449; F 1,16 = 13.2; p ± 0.005; 95% confidence interval for r 0.336–0.867). A mean systolic blood pressure of 140 mmHg or below was associated with no significant decline in GFR over a median period of 13 months. Systolic blood pressure accounted for nearly half of the variability in GFR and a mean systolic pressure of 140 mmHg or below may represent a marker for ‘ideal’ blood pressure treatment. The normal wide variations in protein and phosphate intake between subjects did not significantly influence the rate at which renal function was lost.