There are millions of people across the globe who are suffering from CKD and many of them have to take up RRT to sustain their life while some die without access to RRT. Actual burden may be far more than reported as due to limited awareness about the severity of the disease and lack of epidemiological data there is a serious possibility of underestimation of the burden of CKD. This might have severe repercussions in future especially in regions with inadequate health systems. People with ESKD are at higher risk of mortality in comparison to the general population. The damage to their kidneys are irreversible and management strategies of CKD are aimed at treatment of existing conditions like controlling BP, diabetes and decreasing albuminuria. Important treatment goals for CKD management includes reducing the risk of heart disease by BP management and reduction of albuminuria. Costs of treating people with ESKD have been estimated to be about 10 times more than that of CKD management (2). Nutritional strategies like modifying sodium intake may help in preserving renal function and defer the initiation of RRT. There are many studies conducted to assess the effects of low sodium diets on BP and renal parameters (25, 26, 27). However, there is large heterogeneity in the effects of the interventions reported by different studies. Moreover, from a broader perspective, one needs to find the overall effect of interventions under consideration on different outcomes. Thus, we decided to perform a meta-analysis of RCTs to test the hypothesis that dietary sodium restriction reduces BP and renal parameters and also to quantify overall effects in terms of pooled mean difference. We were able to assess the effects of sodium dietary restrictions on BP and renal parameters such as serum creatinine, serum urea and eGFR. However, albuminuria could not be meta-analyzed.
Our study indicated that sodium restriction promises to be a modifiable risk factor for reducing cardiovascular risk and ESKD progression. Earlier meta-analyses (25, 26, 27) have all showed that reduction in dietary sodium has reduced BP and proteinuria which are the cornerstones of CKD management. Thus, present study has endorsed the findings of earlier studies. High sodium intake is associated with risk factors for both heart disease and can cause severe damage to the kidneys. High sodium intake also has a positive association with high BP, proteinuria and fluid overload. Hence, it becomes doubly important for people with CKD to adopt a low sodium dietary regime due to its role in salt balance (12). Further, low-sodium diet can also reduce arterial stiffness and left ventricular diastolic dysfunction (28, 29).
In the present meta-analysis of RCTs, we tried to find whether sodium restriction is efficacious and if it produces significant improvement in systolic BP, diastolic BP and renal parameters like serum creatinine, serum urea and eGFR. Our systematic search strategy after applying the pre-defined inclusion and exclusion criteria yielded 7 studies (8 reports) which included 465 participants enrolled in restricted sodium intake versus control. The minimum follow-up period for inclusion of studies for meta-analysis was four weeks. The RCTs were conducted in as many as 6 countries namely - Australia, Canada, Korea, Japan, United States of America and Netherlands with majority of them being conducted in renal clinic settings. The risk of bias in the studies included in this review appears to be low and unclear. All the studies included in the review had used some sort of randomization technique with 4 of them providing the exact method of randomization. 3 studies had blinded their participants while the other studies were either crossover study designs or had not reported the allocation concealment clearly. The losses due to follow-up were mentioned in 3 studies while the rest did not exactly specify the reasons for the losses. Also, all studies which were included in the review had clearly reported the outcome measurements across the intervention and control groups.
This study possessed some limitations that need to be considered along with the conclusions. Main limitation was non-inclusion of the studies demanding money for access. Studies included had a follow-up for short durations and hence primary endpoints such as mortality or CVDs could not be assessed and this might also be a possible reason for the differential effects on serum urea, serum creatinine and eGFR. Among the studies included in the review, there was limited evidence to study related outcome measurements such as albuminuria, serum uric acid, serum potassium etc. We were also not able to study the effects of intervention across different stages of CKD due to the insufficient sample size. To overcome these limitations, a major study with enough budgetary provisions may be conducted.
In conclusion, our study found that restricted salt intake could significantly reduce systolic BP and diastolic BP. This low-cost intervention would be a really good strategy to reduce BP and defer the initiation of RRT. Further, multi-center RCTs for longer durations across different stages of CKD could effectively assess the effects of restricted sodium intake on vital renal and cardio vascular parameters. Such study designs could also help clinicians identify the optimal intake of dietary sodium to achieve better renal and cardio vascular outcomes. Therefore, such studies are recommended.