Salt intake, hypertension and diabetes mellitus

Diabetes mellitus affects approximately 135 million people in the world. Diabetes and hypertension are both relatively common diseases in westernised countries. Both entities increase with age. Essential hypertension accounts for the majority of hypertension in people with type 2 diabetes, who constitute more than 90% of those with a dual diagnosis of diabetes and hypertension. The benefit conferred per mm Hg blood pressure reduction appears to be greater in persons with type 2 diabetes than in those with hypertension and non-coexistent diabetes mellitus. Similar to a subset of patients with essential hypertension, type 2 diabetic patients manifest dietary NaCl-induced exacerbation of hypertension. Recent guidelines have emphasised that the target blood pressure levels for patients with diabetes should be lower than in other hypertensive groups. An increased total body sodium and enhanced vascular reactivity are found in people with diabetes and most type 2 diabetic patients are salt sensitive. Type 2 diabetes with hypertension is associated with reduced renal plasma flow when dietary salt intake is high. Experimental, observational and interventional evidence support the benefits of sodium restriction in hypertensives. However, the full effects of sodium restriction are usually not obvious for at least 5 weeks. Other favourable effects of moderate reduction in sodium intake are a regress left ventricular hypertrophy, decrease in diuretic-induced potassium wastage, reduction in proteinuria, protection against stroke and from osteoporosis and renal stones, and enhancement of the antihypertensive effect of the antihypertensive agents.