| Summary: | Background: Raised blood pressure is associated with increased risk of heart disease, impaired endothelial function, structural and functional abnormalities in large and small vessels. It has been shown that dietary sodium and potassium intake play an important role in regulating blood pressure. One of sodium's major functions is to regulate blood volume and pressure including the flexibility of the blood vessels. Increased sodium intake contributes development of hypertension. On the other hand an increased potassium intake lowers blood pressure and experimental studies have shown beneficial effect on endothelial function, vasculature and heart. Previous studies have predominantly used potassium chloride whereas potassium in fruit and vegetables - the main dietary sources of potassium - exists as other types of potassium salt. Aims: The purpose of this work is to study the effect of changing dietary sodium and potassium intake on blood pressure, heart, large and small vasculature and endothelial function. Methods: We carried out two double blind randomized control trials and included 187 subjects in modest salt reduction study and 46 subjects in potassium supplementation study. In the salt reduction study participants were allocated in random order to take 90mmol slow sodium tablets or placebo tables daily for 6 weeks then crossed over to take the opposite. Participants were on a reduced salt intake throughout the whole study. In the potassium supplementation study participants were allocated to take 64mmol potassium chloride (KCL) or bicarbonate (KHC03) or placebo tablets for 4 weeks in the randomised crossover design. We measured BP, large vessel property using PWV and 2D imaging of proximal part of ascending aorta, echocardiographic parameters of LV mass and function. Microcirculation changes were measured by capillaroscopy and orthogonal polarization spectral imaging (OPS). Endothelial function was performed using FMD. Additionally albumin excretion, renin angiotensin aldosteron system activity and bone metabolism parameters were measured. Results: Modest salt reduction study showed significant decrease in BP, urinary albumin excretion, albumin/creatinine ratio and PWV. Echocardiographic parameters remained unaltered. Subgroup analysis showed significant reductions in BP and urinary albumin/creatinine ratio and PWV in blacks. We observed an increase in capillary density in all ethnic groups. Potassium supplementation did not affect office BP and only 24-h and day-time systolic BP was lower with KCL. Compared to placebo, both potassium salts significantly improved endothelial function, increased arterial compliance, decreased LV mass, and improved LV diastolic function. Increased capillary density was seen only when measured by OPS. The study also showed that KCL reduced urinary albumin excretion, and KHC03 improved bone metabolism. Conclusions: These results demonstrate that a modest reduction in salt intake, causes significant falls in BP, reduces urinary albumin excretion and improves large artery compliance in all 3 ethnic groups. Also improvement in both functional and structural capillary rarefaction was observed. Results of potassium supplementation demonstrated that an increase in potassium intake had beneficial effects on the cardiovascular system and KHC03 may improve bone health.
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