Published in The Hindu on August 11, 2011
There is “no strong evidence” to conclude that cutting down the amount of salt consumed every day reduces the likelihood of normal people or those with hypertension dying or experiencing cardiovascular diseases (CVD). This is the finding of a Cochrane Review published recently in the American Journal of Hypertension (AJH) . The study was based on a meta-analysis of seven randomised controlled trials involving 6,250 participants who were followed up for at least six months. The meta-analysis covered people with normal blood pressure, hypertension, and those with heart failure. The finding, which comes in a line of dubious studies published in reputed medical journals, flies in the face of an overwhelming body of evidence showing a clear link between reduced salt intake and health benefits. Unsurprisingly, the results attracted wide publicity in the electronic and print media. But a comment published by Feng J He and Graham A MacGregor in The Lancet exposes the limitations of the Cochrane Review study and tries to undo the damage. It shows that the paper by Rod Taylor of the University of Exeter and others in the AJH is scientifically flawed on major counts. The data of normal and hypertensive patients that enabled Taylor to arrive at the conclusion were not statistically powered; in fact, a re-analysis of the combined data by He and MacGregor revealed that there was a significant 20 per cent reduction in cardiovascular events when the daily salt intake was reduced by 2.0-2.3 grams. Another major flaw was the inclusion of the trial involving heart failure patients without undertaking the necessary adjustments.
It is well known that increased salt intake poses a major challenge to the kidneys’ ability to flush out the sodium. Greater salt intake leads to increased water retention in the body, which is one of the major factors in the development of hypertension. The evidence of a salt-BP link comes from a variety of sources — animal studies, human genetic, epidemiological, migration, population-based intervention, and treatment studies. According to a 2008 paper in the Journal of Human Hypertension , elevated blood pressure alone is responsible for 62 per cent of strokes and 49 per cent of coronary heart disease worldwide. Denial in the face of all this evidence is dangerous. All efforts should be aimed at following the World Health Organisation’s recommendation that people should cut down the daily salt intake to 5 grams, eat more fruits and vegetables, and exercise regularly.