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Less Salt Linked To Reduced Cardiovascular Disease And Death
Article Date: 20 Apr 2007 - 11:00 PDT
US scientists studying a group of people with bordeline to high blood pressure have found that those who lowered their salt intake significantly reduced their risk of getting cardiovascular disease and also of dying from it.
The study is published in the British Medical Journal (BMJ).
The research was conducted by Dr Nancy Cook from Brigham and Women's Hospital and Harvard Medical School in Boston, Massachusetts, and colleagues from other research centres including the National Heart, Lung, and Blood Institute, Bethesda, and Johns Hopkins University, Baltimore, Maryland.
Dr Cook and her team found that people who were pre-hypertensive and cut back on salt intake reduced their chances of developing cardiovascular disease by a quarter, and their risk of dying from it by up to one fifth.
Cardiovascular disease is an umbrella term for a group of diseases that affect the heart or arteries. Examples include strokes and heart disease.
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Previous studies have suggested that eating less salt lowers blood pressure, but until this study there was no objective evidence linking salt reduction to long term reduction in cardiovascular disease risk, said the researchers.
Dr Cook and her colleagues followed up people who took part in two trials that were completed in the 1990s, called the Trials of Hypertension Prevention (TOHP). The trials were designed to analyse the effect of reducing dietary salt on blood pressure.
All the people in the two TOHP trials were aged 30 to 54 and had borderline verging on high blood pressure or "pre-hypertensive". This put them at greater risk of getting cardiovascular disease.
TOHP trial 1 included 744 people and ended in 1990.
TOHP trial 2 included 2,382 people and ended in 1995.
Participants in both trials were randomized to either the intervention group or a control group (no intervention). Follow up took place 10 to 15 years after the trials.
The intervention comprised education and advice on the benefits and how to reduce dietary salt, that lasted for 18 months in TOHP 1 and between 3 and 4 years in TOHP 2.
The results showed that:
-- Information was obtained on 2,415 participants (77.3 per cent).
-- 133 of them had a significant cardiovascular event (myocardial infarction, stroke, coronary revascularisation) and 67 died.
-- In both trials, the intervention groups reduced dietary salt consumption by between 25 and 35 per cent.
-- Net sodium reductions in the TOHP 1 intervention group was 44 mmol/24 h.
-- In the TOHP 2 intervention group this figure was 33 mmol/24 h.
-- The control groups did not reduce their dietary salt intake.
-- Risk of cardiovascular event was 25 per cent lower in the intervention groups.
-- This figure was independent of trial, clinic, age, race and sex.
-- After adjusting for baseline sodium excretion and weight, the figure went even lower, to 30 per cent.
-- Risk of death due to cardiovascular disease was up to 20 per cent lower in the intervention groups.
The researchers concluded that:
"Sodium reduction, previously shown to lower blood pressure, may also reduce long term risk of cardiovascular events."
Speculating on their findings, Dr Cook and colleagues suggested that sodium may act directly by making vessel walls stiffer, making them less pliable and able to expand and contract when needed. It could have a similar effect on heart cells, they said.
Critics of the study point out that the participants were already pre-hypertensive, and therefore it does not support the notion that healthy people with normal blood pressure would benefit from reducing dietary salt.
In the UK the government has mounted a strong campaign to get people to eat less salt -- they want to bring the daily average of 9g down to 6g, which nutritionists say is ambitious but achievable if people watch what they eat and read all their food labels.
Nearly three quarters of the recommended daily amount is likely to be in the food that consumers buy, suggesting the onus is on manufacturers to reduce the amount they add, increase healthy choices and provide better information (for instance sodium and salt content are not the same and can be confused with each other).
The Food Standards Agency (FSA) in the UK says it is working closely with the food industry to work towards the salt reduction target.
"Long term effects of dietary sodium reduction on cardiovascular disease outcomes: observational follow-up of the trials of hypertension prevention (TOHP)."
Nancy R Cook, Jeffrey A Cutler, Eva Obarzanek, Julie E Buring, Kathryn M Rexrode, Shiriki K Kumanyika, Lawrence J Appel, Paul K Whelton.
BMJ 2007:391476048, doi:10.1136/bmj.39147.604896.55
Published online 20 April 2007.
Click here for Abstract.
Click here for Salt, is Your Food Full of It? (FSA, UK).
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