Relationship between low-normal blood pressure and kidney disease in type 1 diabetes

Current recommendations, largely based on studies in type 2 diabetes, suggest lower target blood pressures (BPs) for individuals with diabetes than for the general population. However, the effect of lower BP on renal outcomes in type 1 diabetes is uncertain. In a population-based cohort of type 1 diabetes adults (mean age: 33.1 years) based in Wisconsin, of which the distribution of baseline BP was in the low-normal range, we examined the relationship between decreasing categories of systolic and diastolic BP and the 16-year incidence of proteinuria (n=232 of 604) and estimated glomerular filtration rate of <60 mL/min/1.73 m(2) (n=158 of 547). Decreasing BP categories had lower relative risk (RR) of developing incident proteinuria (RR comparing decreasing quartiles of systolic BP: 1.00, 0.76, 0.58, 0.73; P for trend=0.03; RR comparing decreasing quartiles of diastolic BP: 1.00, 0.81, 0.66, 0.42; P for trend <0.0001) and incident estimated glomerular filtration rate <60 mL/min/1.73 m(2) (RR comparing decreasing quartiles of systolic BP: 1.00, 0.83, 0.61, 0.65; P for trend=0.03; RR comparing decreasing quartiles of diastolic BP: 1.00, 0.84, 0.82, 0.43; P for trend=0.001). These associations were independent of glycemic control and several putative confounding factors. Subjects with either systolic BP <120 mm Hg or diastolic BP <70 mm Hg had significantly lower RR (95% confidence interval) of incident proteinuria (0.63 [0.48 to 0.82]) and incident estimated glomerular filtration rate <60 mL/min/1.73 m(2) (0.60 [0.43 to 0.82]); corresponding population-attributable risks for these outcomes were 26.7% and 29.5%, respectively. Our study suggests that lower BP levels, even below the accepted normal range, are protective against kidney disease in adults with type 1 diabetes. Interventional trials are desirable to clarify the clinical significance of this association.