Salt intake and hypertension: walking the tight rope.

H a disease often correlated to affluence, is becoming increasingly common in urban population in developing countries. Recent epidemiological studies in India show that prevalence was 1.2 to 4.2 % in 1940’s and has remarkably increased to nearly 15 to 25% in 1990’s in urban areas. A recent study by Mohan et al1 reports a prevalence of 20% in Chennai in the CURES study. Rural areas also showed a similar increase in prevalence of hypertension (~5-10%) although the rise was not as steep as in urban areas.2 The etiology of hypertension is considered to be multifactorial which includes genetic, dietary, racial, metabolic and psychological factors, often in combination. Hypertension is considered to be etiologically related to obesity and insulin resistance and is a component of the metabolic syndrome. A genetic role is implicated as hypertension is seen to be about twice as common in subjects who have one or both hypertensive parents. Perinatal influences may also play a role.3 Low birth weight and catch-up obesity seems to adversely affect blood pressure in adult life.4 Further, low grade inflammation manifesting as raised C-reactive protein levels may also be a novel correlate of hypertension.5 Salt or body sodium level is considered to be one of the important contributing factors in the pathogenesis of hypertension. Going as far back as 2,000 B.C., the famous Chinese “Yellow Emperor” Huang Ti demonstrated the association of salt with a “hardened pulse”. Since then, evidence from many population-based studies have demonstrated a positive association.6-10 The “Dietary Approaches to Stop Hypertension (DASH) study” demonstrated a direct relationship between salt intake and blood pressure. The subjects put on DASH diet, containing high amount of fiber, vegetables and fruits, with low fat dairy products and low salt processed foods experienced a reduction of blood pressure by 11/6 mm Hg. In this study, diets at three sodium levels were compared: high (3,300 mg), intermediate (2,400 mg) and low (1,500 mg). The difference in blood pressure in those taking lowest sodium-containing diet to highest sodium-containing diets was 8.3/4.4 mm Hg in patients with hypertension and by 5.6/2.8