Background: Although evidence shows that reduced sodium intake lowers blood pressure, some studies suggest that sodium reduction may adversely affect insulin resistance and glucose tolerance.
Objectives: The objectives were to assess the effects of sodium reduction on glucose tolerance, evaluate strengths and weaknesses of the relevant scientific literature, and provide direction for future research.
Methods: We searched The Cochrane Library, MEDLINE, EMBASE, CINAHL, and Web of Science through August 2014. Both randomized and nonrandomized intervention trials were included in our meta-analyses. The effects of sodium reduction on glucose tolerance were evaluated in 37 articles, but because of a lack of comparable data, 8 trials were excluded from the meta-analyses.
Results: Participants were 10-79 y old, either primarily healthy or with hypertension. In meta-analyses of 20 randomized, crossover trials (n = 504 participants) and 9 nonrandomized crossover trials (n = 337), circulating glucose concentrations of fasting participants were not affected by reduction in sodium intake. In contrast, in meta-analyses of 19 of the 20 randomized, crossover trials (n = 494), fasting insulin concentrations were 9.53 pmol/L higher (95% CI: 5.04, 14.02 pmol/L higher) with sodium reduction. In 9 nonrandomized trials (n = 337), fasting insulin did not differ with reduced sodium intake. Results differed little when the analyses were restricted to studies with a low risk of bias and duration of ≥7 d.
Conclusions: This meta-analysis revealed no evidence that, in trials with a short intervention and large reductions in sodium, circulating glucose concentrations differed between groups. Recommendations for future studies include extending intervention durations, ensuring comparability of groups at baseline through randomization, and assessing sodium intakes relevant to population sodium reduction. In addition, analyses on other metabolic variables were limited because of the number of trials reporting these outcomes and lack of consistency across measures, suggesting a need for comparable measures of glucose tolerance across studies.
Keywords: fasting glucose; insulin resistance; meta-analysis; sodium reduction; systematic review.
© 2015 American Society for Nutrition.