A meta-analysis of randomised controlled trials (RCT) among healthy normotensive and essential hypertensive elderly patients to determine the effect of high salt (NaCl) diet on blood pressure

To examine the effect of chronic NaCl ingestion on blood pressure (BP) in the elderly, a meta-analysis was undertaken of 11 randomised controlled trials of which five included patients greater than or equal to 60 years of age only and six included patients with a mean age close to 60 years. The following databases were used: Medline, Embase, Current Contents, The Cochrane Library, the AMI and IPA databases. Mean erect systolic and diastolic blood pressures (SBP/DBP) on chronic (greater than or equal to 9 weeks) high and low NaCl diets were recorded, the pooled mean effect, the pooled standard error and 95% confidence intervals (CI) were calculated and linear regression was used to evaluate the potential association between NaCl intake and BP. When all trials were pooled, a chronic high NaCl diet significantly increased mean SEP and DBP by 5.58 mm Hg (95%Cl 4.31-6.85) and 3.5 mm Hg (95%Cl 2.62-4.38) respectively. There was a significant association between the level of NaCl intake and SEP (P = 0.05, r(2) = 0.37) but not DBP (P = 0.76, r(2) = 0.01). When trials were pooled separately, a chronic high NaCl diet increased SEP by 5.46 mm Hg (95%Cl 3.56-7.36) and DBP by 2.63 mm Hg (95%Cl 1.18-4.08) in trials including patients greater than or equal to 60 years of age only, and increased SEP by 3.27 mm Hg (95%Cl 1.23-5.31) and DBP by 2.69 mm Hg (95%Cl 1.44-3.94) in trials including patients with a mean age close to 60 years. These data suggest that a chronic high NaCl diet in elderly patients with essential hypertension is associated with an increase in SEP and DBP, the association is significant for both SEP and nap but more marked for SEP than DBP, the effect is more pronounced the older the patient and NaCl dose strongly predicts SEP in older patients.