New research first to prove that salt reduction

28th July

A new study , published in the journal Hypertension, shows for the first time that a modest reduction in salt intake (from around 10g to 5g of salt per day) in black patients with hypertension results in both a fall in blood pressure (the major risk factor for cardiovascular disease) and urinary protein excretion (the major risk factor for renal disease and an independent risk factor for cardiovascular mortality in the elderly and people with hypertension or diabetes).  

Raised blood pressure is more common in black people than white people, leading to a higher risk of cardiovascular events, particularly strokes, than in the general population .  Hypertension-related renal (kidney) disease occurs four to six times more often in black people than in white people .  Previous research has suggested that black individuals have a greater blood pressure response to salt reduction than their white counterparts .  And yet this is the first randomised, double-blind, placebo controlled crossover trial to look specifically at the role of dietary salt reduction in lowering blood pressure and urine protein excretion in black people.

In the study, 40 individuals of African or African-Caribbean origin with raised blood pressure on no treatment followed a modestly reduced salt diet for the whole study.  After a two-week run-in period they were then randomised to receive either slow-release sodium chloride tablets designed to bring salt intake back their usual intake for one month or one month of identical matching placebos that contained no salt.  The study groups were then crossed over for a further month.  Salt intake was assessed by the measurement of 24 hr urinary sodium (more than 90% of salt eaten comes out in the urine).  On the slow sodium phase of the study at the end of the month, salt intake was around 10 g/day and on the placebo phase after one month, salt intake was around 5 g of salt/day, the level recommended by the World Health Organisation for all adults.  A reduction in salt intake from 10 g/day to 5 g/day lowered systolic blood pressure by an average of 8 mmHg and diastolic by 3 mmHg.  These falls were sustained over 24 hours.  The reduction in salt intake from 10 to 5 g also resulted in a large reduction in urine protein excretion of 19.4%.

“This new study is very welcome,” says Dr Emma Mast, Project Co-ordinator for Consensus Action on Salt and Health.  “It provides definitive evidence that reducing salt modestly in the diet is particularly beneficial for black people.  As black people are more likely than white people to suffer from the effects of blood pressure, particularly on stroke and kidney disease, we need research in this group that does demonstrate that salt reduction reduces their risk.  The fall in blood pressure seen in this study is equivalent to the fall seen with single drug therapy and means that all black people with high blood pressure should reduce their salt intake to 5g a day or less if possible.”

Dr Pauline Swift, lead author on the paper stressed, “It is the first study to show that a reduction in salt intake reduces the level of protein being excreted in the urine.  This will reduce the risk of developing kidney disease and is also likely to reduce the risk of cardiovascular disease over and above the reduction in risk which occurs with the blood pressure fall.  This is a new and unrecognised benefit of salt reduction”.  

Click here for the full journal article

Notes to editors
• Consensus Action on Salt and Health (CASH) is a group of the UK’s leading experts on salt and its effects on health.  It is working to reach a consensus with the food industry and government over the harmful effects of a high salt diet, and bring about a reduction in the amount of salt in processed foods as well as salt added to cooking and at the table, so that salt intake in the UK is reduced in adults to below 6g a day, and less for children.
References:

References

Pauline A Swift, Nirmala D Markandu, Giuseppe A Sagnella, Feng J He, Graham A MacGregor.  Modest salt reduction lowers blood pressure and urine protein excretion in black hypertensives.  Hypertension. 2005;46:1-5

Cappuccio et al.  Prevalence, detection and management of cardiovascular risk factors in different ethnic groups in south London.  Heart. 1997;78:555-563

Roderick Pj et al.  Population need for renal replacement therapy in Thames regions: ethnic dimensions. BMJ. 1994;309;1111-1114.

Svetkey LP et al.  Effects of dietary patterns on blood pressure: subgroup analysis of the Dietary Approaches to Stop Hypertension (DASH) randomized clinical trial. Arch Intern Med. 1999;159:285-293.