Salt Reduction on Blood Pressure and Cardiovascular Organ Damage

Effects of Modest Salt Reduction on Blood Pressure and Markers of Target Organ Damage in Patients With Untreated Essential Hypertension or Prehypertension

The purpose of this study is to determine the effect of a modest reduction in salt intake on blood pressure in white, black and Asian individuals with hypertension or prehypertension, and also to determine whether a modest reduction in salt intake has beneficial effects on the surrogate markers of target organ damage in cardiovascular disease.

The average salt intake for adults in the UK is approximately 10-12 g/day. The current recommendations are to reduce salt intake to 5-6 g/day or less. Many randomised trials have shown that this reduction in salt intake has a significant effect on blood pressure, however, most previous trials were carried out in white individuals, fewer in blacks, and none in Asians.

Increasing evidence from epidemiological studies in humans and experimental studies in animals suggest that that our current high salt intake may have other harmful effects on cardiovascular health e.g. a direct effect on stroke, left ventricular hypertrophy, progression of renal disease and proteinuria independent of and additive to salt's effect on blood pressure. However, no well-controlled trials have studied whether a modest reduction in salt intake has beneficial effects on the surrogate markers of target organ damage in cardiovascular disease.

We propose to carry out a double-blind randomised trial to study the effects of a modest reduction in salt intake, as currently recommended, on blood pressure and target organ damage assessed by the measurements of 24 hour urinary albumin excretion, left ventricular mass, left ventricular diastolic function, pulse wave velocity and capillary density, in white, black and Asian individuals with hypertension or prehypertension.

Comparisons: Usual salt intake compared to reduced salt intake.

Inclusion Criteria:

• Patients with untreated essential hypertension or prehypertension (sitting systolic blood pressure between 120 and 170 mmHg and/or sitting diastolic blood pressure between 80 and 105 mmHg)
• Age 18 - 75 years.

Exclusion Criteria:

• Individuals younger than 18 or older than 75 years
• Individuals with severe hypertension i.e. blood pressure > 170/105 mmHg
• Individuals with any secondary cause of hypertension
• Individuals with impaired renal function with plasma creatinine greater than 150 umol/L
• Individuals with diabetes mellitus
• Individuals with malignancy or liver disease
• Individuals with ischaemic heart disease or heart failure
• Females who are pregnant or breast feeding or on the oral contraceptive pill.