Does altering dietary salt intake aid in the prevention and treatment of diabetic kidney disease?

There is strong evidence that our current consumption of salt is a major factor in increasing blood pressure (BP), whether BP levels are normal or raised. Diabetes makes it more likely to develop high BP, which increases the risk of strokes, heart attacks and speeds up the progression of diabetic kidney disease. This review found 13 studies including 254 patients with type 1 and type 2 diabetes. Reducing salt intake by 8.5 g/day lowered BP by 7/3 mm Hg. Public health guidelines recommend reducing dietary salt intake to less than 5-6 g/day and people with diabetes would benefit from reducing salt in their diet to at least this level.

Authors' conclusions: 

Although the studies are not extensive, this meta-analysis shows a large fall in BP with salt restriction, similar to that of single drug therapy. All diabetics should consider reducing salt intake at least to less than 5-6 g/day in keeping with current recommendations for the general population and may consider lowering salt intake to lower levels, although further studies are needed.

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Background: 

There is strong evidence that our current consumption of salt is a major factor for increased blood pressure (BP) and a modest reduction in salt intake lowers BP whether BP levels are normal or raised. Tight control of BP in diabetics lowers the risk of strokes, heart attacks and heart failure and slows the progression of diabetic kidney disease (DKD). Currently there is no consensus in restricting salt intake in diabetic patients.

Objectives: 

To evaluate the effect of altered salt intake on BP and markers of cardiovascular disease and DKD.

Search strategy: 

In January 2010, we searched the Cochrane Renal Group's Specialised Register, CENTRAL (in The Cochrane Library), MEDLINE (from 1966) and EMBASE (from 1980) to identify appropriate articles.

Selection criteria: 

We included all randomised controlled trials of salt reduction in individuals with type 1 and type 2 diabetes.

Data collection and analysis: 

Two authors independently assessed studies and resolved differences by discussion with a third independent author. We calculated mean effect sizes using both the fixed-effect and random-effects models.

Main results: 

Thirteen studies (254 individuals) met our inclusion criteria. These included 75 individuals with type 1 diabetes and 158 individuals with type 2 diabetes. The median reduction in urinary sodium was 203 mmol/24 h (11.9 g/day) in type 1 diabetes and 125 mmol/24 h (7.3 g/day) in type 2 diabetes. The median duration of salt restriction was one week in both type 1 and type 2 diabetes. BP was reduced in both type 1 and type 2 diabetes. In type 1 diabetes (56 individuals), salt restriction reduced BP by -7.11/-3.13 mm Hg (systolic/diastolic); 95% CI: systolic BP (SBP) -9.13 to -5.10; diastolic BP (DBP) -4.28 to -1.98). In type 2 diabetes (56 individuals), salt restriction reduced BP by -6.90/-2.87 mm Hg (95% CI: SBP -9.84 to -3.95; DBP -4.39 to -1.35). There was a greater reduction in BP in normotensive patients, possibly due to a larger decrease in salt intake in this group.