Glomerular charge and size selectivity assessed by changes in salt intake in type 2 diabetic patients

Altered dietary salt intake for preventing diabetic kidney disease and its progression

BACKGROUND

There is strong evidence that our current consumption of salt is a major factor in the development of increased blood pressure (BP) and that a reduction in our salt intake lowers BP, whether BP levels are normal or raised initially. Effective control of BP in people with diabetes lowers the risk of strokes, heart attacks and heart failure and slows the progression of chronic kidney disease (CKD) in people with diabetes. This is an update of a review first published in 2010.

OBJECTIVES

To evaluate the effect of altered salt intake on BP and markers of cardiovascular disease and of CKD in people with diabetes.

SEARCH METHODS

We searched the Cochrane Kidney and Transplant Register of Studies up to 31 March 2022 through contact with the Information Specialist using search terms relevant to this review. Studies in the Register were identified through searches of CENTRAL, MEDLINE, and EMBASE, conference proceedings, the International Clinical Trials Register (ICTRP) Search Portal and ClinicalTrials.gov.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) of altered salt intake in individuals with type 1 and type 2 diabetes. Studies were included when there was a difference between low and high sodium intakes of at least 34 mmol/day.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed studies and resolved differences by discussion. We calculated mean effect sizes as mean difference (MD) and 95% confidence intervals (CI) using the random-effects model. Confidence in the evidence was assessed using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach.

MAIN RESULTS

Thirteen RCTs (313 participants), including 21 comparisons (studies), met our inclusion criteria. One RCT (two studies) was added to this review update. Participants included 99 individuals with type 1 diabetes and 214 individuals with type 2 diabetes. Two RCTs (four studies) included some participants with reduced overall kidney function. The remaining studies either reported that participants with reduced glomerular filtration rate (GFR) were excluded from the study or only included participants with microalbuminuria and normal GFR. Five studies used a parallel study design, and 16 used a cross-over design. Studies were at high risk of bias for most criteria. Random sequence generation and allocation concealment were adequate in only three and two studies, respectively. One study was at low risk of bias for blinding of participants and outcome assessment, but no studies were at low risk for selective reporting. Twelve studies reported non-commercial funding sources, three reported conflicts of interest, and eight reported adequate washout between interventions in cross-over studies. The median net reduction in 24-hour urine sodium excretion (24-hour UNa) in seven long-term studies (treatment duration four to 12 weeks) was 76 mmol (range 51 to 124 mmol), and in 10 short-term studies (treatment duration five to seven days) was 187 mmol (range 86 to 337 mmol). Data were only available graphically in four studies. In long-term studies, reduced sodium intake may lower systolic BP (SBP) by 6.15 mm Hg (7 studies: 95% CI -9.27 to -3.03; I² = 12%), diastolic BP (DBP) by 3.41 mm Hg (7 studies: 95% CI -5.56 to -1.27; I² = 41%) and mean arterial pressure (MAP) by 4.60 mm Hg (4 studies: 95% CI -7.26 to -1.94; I² = 28%). In short-term studies, low sodium intake may reduce SBP by 8.43 mm Hg (5 studies: 95% CI -14.37 to -2.48; I² = 88%), DBP by 2.95 mm Hg (5 studies: 95% CI -4.96 to -0.94; I² = 70%) and MAP by 2.37 mm Hg (9 studies: 95% CI -4.75 to -0.01; I² = 65%). There was considerable heterogeneity in most analyses but particularly among short-term studies. All analyses were considered to be of low certainty evidence. SBP, DBP and MAP reductions may not differ between hypertensive and normotensive participants or between individuals with type 1 or type 2 diabetes. In hypertensive participants, SBP, DBP and MAP may be reduced by 6.45, 3.15 and 4.88 mm Hg, respectively, while in normotensive participants, they may be reduced by 8.43, 2.95 and 2.15 mm Hg, respectively (all low certainty evidence). SBP, DBP and MAP may be reduced by 7.35, 3.04 and 4.30 mm Hg, respectively, in participants with type 2 diabetes and by 7.35, 3.20, and 0.08 mm Hg, respectively, in participants with type 1 diabetes (all low certainty evidence). Eight studies provided measures of urinary protein excretion before and after salt restriction; four reported a reduction in urinary albumin excretion with salt restriction. Pooled analyses showed no changes in GFR (12 studies: MD -1.87 mL/min/1.73 m², 95% CI -5.05 to 1.31; I² = 32%) or HbA1c (6 studies: MD -0.62, 95% CI -1.49 to 0.26; I² = 95%) with salt restriction (low certainty evidence). Body weight was reduced in studies lasting one to two weeks but not in studies lasting for longer periods (low certainty evidence). Adverse effects were reported in only one study; 11% and 21% developed postural hypotension on the low-salt diet and the low-salt diet combined with hydrochlorothiazide, respectively.

AUTHORS' CONCLUSIONS

This systematic review shows an important reduction in SBP and DBP in people with diabetes with normal GFR during short periods of salt restriction, similar to that obtained with single drug therapy for hypertension. These data support the international recommendations that people with diabetes with or without hypertension or evidence of kidney disease should reduce salt intake to less than 5 g/day (2 g sodium).

Effects of the Dietary Approaches to Stop Hypertension Diet and Sodium Reduction on Blood Pressure in Persons With Diabetes

Elevated blood pressure and blood pressure-related morbidity are extraordinarily common in persons with diabetes. The Dietary Approaches to Stop Hypertension dietary pattern and dietary sodium reduction are recommended as lifestyle interventions in individuals with diabetes. However, these recommendations have largely been based on studies conducted in persons without diabetes. In this review, we summarize available evidence from trials that tested the effects of these 2 dietary interventions on blood pressure in people with diabetes. Overall, of the 3 trials (total n=151) that tested the effects of the Dietary Approaches to Stop Hypertension dietary pattern in persons with diabetes, 2 trials documented that the Dietary Approaches to Stop Hypertension dietary pattern lowered blood pressure. While 16 trials (total n=445) tested the effects of sodium reduction in persons with diabetes, results were inconsistent, likely because of design limitations, for example, brief duration, small sample size, and low baseline blood pressure levels, as well as differences in the mode of intervention delivery (behavioral interventions, feeding studies, and sodium supplements). In conclusion, there is a substantial need for additional research on the blood pressure lowering effects of the Dietary Approaches to Stop Hypertension diet and sodium reduction in people with diabetes and hypertension, given the high prevalence of hypertension and the dearth of high-quality trials in this population.

Renal function in relation to sodium intake: a quantitative review of the literature

We undertook a quantitative literature review to search for evidence underpinning current guidelines proposing a reduction of sodium intake to less than 2.4 g/d for the management of chronic kidney disease. We searched PubMed for peer-reviewed articles published from January 1980 through May 2016. Two investigators screened 5072 publications and extracted data from 36, including 11 cross-sectional and 5 longitudinal observational studies and 20 intervention trials. Within-study effect sizes were pooled and standardized to a sodium gradient of 100 mmol/d by using inverse-variance weighted random effects models. Among cross-sectional studies, the pooled odds ratio for albuminuria was 1.23 (95% confidence interval [CI], 0.92-1.64, P = 0.16), and the pooled mean difference in glomerular filtration rate amounted to 8.5 ml/min (CI, -2.3 to 19.2 ml/min; P = 0.12). In the cohort studies, the pooled relative risk of a renal endpoint was 1.08 (CI, 0.92-1.29; P = 0.35). In the intervention trials (median duration, 14 days [range, 4-186 days]), the mean differences in estimated glomerular filtration rate and albuminuria (high vs. low sodium intake) averaged 4.6 ml/min (CI, 3.4-5.8 ml/min; P < 0.0001) and 53% (CI, 21-84; P = 0.001), respectively. Cochran's Q statistic indicated significant heterogeneity among cross-sectional studies for both estimated glomerular filtration rate and albuminuria (P < 0.0001) and among intervention trials for albuminuria (P = 0.04). In conclusion, there is no robust evidence suggesting that long-term reduction of salt intake would prevent chronic kidney disease or delay its progression. However, our current findings, which were mainly obtained in people with slight renal impairment, cannot be extrapolated to patients with moderate or severe chronic kidney disease.

Salt Restriction in Diabetes

There are no long-term interventions examining the effects of salt reduction in people with diabetes, and these are urgently required. Sodium reduction is controversial as it appears that an intake below 2.5 g and above 6 g/day of salt is associated with increased cardiovascular disease risk. However, pre-existing illness leading to a lower salt intake may confound the findings. Only a few studies have prospectively collected data on the sodium intake and excretion of people with diabetes and examined hard end points. In addition, future studies need to collect more data on food intake as well as coexistent illnesses to address potential confounding. The World Health Organization recommends a reduction to less than 5 g/day salt in adults. Given that the available evidence suggests that the salt intake of people with type 2 diabetes is generally well above 6 g/day it seems reasonable to ensure individuals with diabetes have an intake below 6 g/day. However, such recommendations need to be individualized.

Increased Urine IgM and IgG(2) Levels, Indicating Decreased Glomerular Size Selectivity, Are Not Affected by Dalteparin Therapy in Patients with Type 2 Diabetes

Fifty-four type 2 diabetic patients with neuroischemic foot ulcers were randomised to treatment with 5000 IU of dalteparin, (n = 28), or physiological saline, (n = 26), once daily until ulcer healing or for a maximum of 6 months. Thirty-three patients had normo-, 15 micro-, and 6 macroalbuminuria. The urinary levels of IgM and IgG₂ were elevated in 47 and 50 patients, respectively. Elevated urinary levels of IgM and IgG₂ indicate decreased glomerular size selectivity. Urine IgM levels were associated with IGF-1/IGFBP-1 and IGFBP-1 levels. Dalteparin treatment increased urinary levels of glycosaminoglycans (P < 0.001) and serum IGFBP-1 (P < 0.05) while no significant effects were seen in any of the other studied parameters. In conclusion, dalteparin therapy in patients with type 2 diabetes had no effects on urinary levels of albumin, IgM, or IgG₂ despite significantly increased glycosaminoglycans in urine. Elevated urinary levels of IgM and IgG₂ might be more sensitive markers of renal disease than albuminuria in patients with type 2 diabetes and antihypertensive therapy.

Altered dietary salt intake for preventing and treating diabetic kidney disease

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.

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.

[Tubular kidney function in patients with type 2 diabetes mellitus, microalbuminuria and proteinuria]

INTRODUCTION

Diabetes mellitus (DM) and hypertension are the most frequent causes of kidney function damage. Many different tests are developed to detect reversible functional kidney changes (detection of microalbuminuria and selective urinary enzymes).

OBJECTIVE

The aim of our study was to examine tubular kidney function in type 2 DM patients with different proteinuria levels, and to compare these results with healthy people.

METHOD

The patients with type 2 DM and creatinine clearance >80 ml/min were included in the study. According to the levels of proteinuria, the patients were classified in three groups: group I--patients with proteinuria <300 mg/24 h, and no microalbuminuria; group II--the patients with proteinuria <300 mg/24 h and microalbuminuria >20 mg/24 h; and group III--the patients with proteinuria >300 mg/24 h. The control group consisted of healthy subjects.

RESULTS

The study revealed that in type 2 DM patients and normal global kidney function, fractional excretions of sodium, potassium, and phosphates as well as renal phosphate concentrations were not adequately sensitive markers to detect damage in tubular kidney function in DM. There were some changes of urate fractional excretion in these patients: this value was significantly lower in patients with microalbuminuria compared with those with proteinuria >300 mg/24 h, as well as in the control group (p < 0.05). Hormone dependent tubular kidney activity, urinary osmolarity, and urea fractional excretion in all patients were within normal ranges.

CONCLUSION

It is evident that routine laboratory analyses are not sensitive markers to detect early changes of kidney function in type 2 DM.

Damage of tubule cells in diabetic nephropathy type 2: urinary N-acetyl-beta-D-glucosaminidasis and gamma-glutamil-transferasis

BACKGROUND/AIM

A damage of tubular epithelial cells is followed by the release of cell enzymes and production of proinflammatory compounds, which lead to the tubulointerstitial damage. The aim of this study was to examine the function of renal tubules in the patients with diabetes mellitus type 2 (DM type 2) and the various proteinuria degrees, to establish the damage of the proximal tubule cells caused by DM type 2 by determining urinary N-acetyl-beta-D-glucosaminidasis (beta-NAG) and gamma-glutamil-transferasis (gamma-GT) activity in urine, as well as to compare the obtained results in the examined groups of patients with the values in the healthy examinees.

METHODS

A complete examination of renal function and selective enzymuria was performed in 37 patients with DM type 2, and 14 healthy examinees as the controls. The patients were divided in three groups according to the degree of proteinuria. The first group consisted of the patients with diabetes without microalbuminuria; the second one consisted of the patients with proteinuria of < 300 mg/24 h, and microalbuminuria of > 20 mg/24 h, while the third one included the patients with proteinuria of > 300 mg/24 h.

RESULTS

In the patients with DM type 2 and the preserved global renal function, fractional excretion of sodium, potassium and phosphates, as well as renal threshold of phosphates concentration, were not sensitive parameters for discovering the damage of the renal tubule function. The determination of beta-NAG activity proved to be the most sensitive parameter for early discovering of tubule cells damages. The difference among the examined groups was statistically highly significant.

CONCLUSION

The increased presence of beta-NAG in the urine of DM type 2 patients, pointed out an early tubular disorder and damage of cells, while gamma-GT was a less sensitive indicator of this damage.

An in-depth review of the evidence linking dietary salt intake and progression of chronic kidney disease

BACKGROUND

Dietary salt has been debated for decades as having a potentially deleterious influence on human health.

OBJECTIVES

To determine the quality of research and the relationship between dietary salt and markers for progression of kidney disease.

METHODS

Data sources included 7 electronic databases comprehensively searched for literature published between January 1, 1966, and August 31, 2004, and a manual search of bibliographies of relevant papers, and consultation with experts in the field. Differences between the paired reviewers were reconciled through consensus or by a content expert.

RESULTS

Sixteen studies met the inclusion-exclusion criteria and were identified for review; however, the study methodologies were extremely heterogeneous. Conclusions commonly cited in the studies include: variations in salt consumption are directly correlated with albuminuria, and an increase in salt consumption is associated with an acute increase in glomerular filtration rate, while a reduction in salt consumption may slow the rate of renal function loss.

CONCLUSIONS

The available published information, while highly variable in methods and quality, suggests that variations in dietary salt consumption directly influence albuminuria, with increasing salt intake associated with worsening albuminuria; however, results are inadequate and conflicting on the effects of dietary salt consumption on renal function, especially over a prolonged time. There was no evidence of a detrimental effect of reduced salt intake. On the other hand, there is consistent experimental evidence to link increased salt exposure with kidney tissue injury. On the basis of these data, we believe that dietary salt restriction should be considered in patients with chronic kidney disease.

Does dietary salt increase the risk for progression of kidney disease?

Due to the inconsistent observations and suboptimal quality of the study designs, there is insufficient clinical evidence to suggest that increased salt intake may adversely modify the rate of progression of kidney disease. However, there is experimental evidence to suggest a link between increased salt exposure and kidney tissue injury. Further clinical trials are needed to evaluate the relationship between dietary salt and risk for progression of chronic kidney disease.