The question as to the role of salt intake in essential hypertension has been controversial in the past but is now more accepted:
- advocates point to the correlation between the salt intake of various populations and the incidence of hypertension and age-related increases in blood pressure
- the INTERSALT (BMJ 18/5/96) study revealed a strong positive association of urinary sodium with systolic pressure of individuals
- a randomised controlled trial has investigated the effect of varying sodium intake in 412 trial participants (blood pressure of participants ranged from 120/80 mmHg to 159/85 mmHg) - results showed that, in general, reduction in sodium intake resulted in a fall in systolic and diastolic blood pressure, whether or not the participant had hypertension (1)
- it is suggested that the salt intake of most populations could be halved without adverse effects and would probably lead to a reduction in the number of individuals requiring anti-hypertensive therapy
- it has been suggested that sodium intake should be reduced to about 100 mmol per day from the current average of about 150 mmol (2) to help reduce the risk of development of cardiovascular disease
- the role of sodium as apposed to salt intake is less disputed - studies have shown hypertensives and their relatives to have deficits in cell membrane sodium transport leading to a high intracellular calcium and heightened vascular reactivity to vasoconstrictive agents
Note - in 2021, the Salt Substitute and Stroke Study (SSaSS) (3) demonstrated a significant reduction in BP, CVD, and death among Chinese adults randomized to a low sodium salt-substitute supplemented with potassium. This trial largely puts to rest any remaining debate about the benefits of dietary sodium restriction among persons with excess baseline intake (dietary sodium intake fell from approximately 5 down to 4 g/day in the active arm of SSaSS).
However, whether achieving and maintaining a dietary sodium of less than1.5 g/day is feasible in real-world settings and whether this low an intake is harmful remain open questions.
Reference:
- Sacks FM et al for the DASH-Sodium Collaborative Research Group (2001). Effects on blood pressure of reduced dietary sodium and the dietary approaches to stop hypertension (DASH) diet. NEJM, 344, 3-10.
- Health Development Agency (2000). Coronary heart disease. Guidance for implementing the preventive aspects of the National Framework. London.
- Neal B et al. Effect of Salt Substitution on Cardiovascular Events and Death. N Engl J Med 2021;385:1067-1077