A well-controlled study with people from three ethnic groups – whites, blacks and Asians – found that reducing salt intake from 9.7 to 6.5 grams per day reduced average blood pressure from 146/91 to 141/88 mmHg within six weeks.
“Our study is the largest double-blind trial of modest salt reduction which also involves a large number of black and Asian participants,” wrote the researchers in Hypertension.
“The study demonstrates that a modest reduction in salt intake, as currently recommended, causes significant and important falls in BP in all three ethnic groups of individuals with mildly raised BP,” they added.
Salt is of course a vital nutrient and is necessary for the body to function, but campaigners for salt reduction, like the Consensus Action on Salt and Health (CASH) consider the average daily salt consumption in the western world, between 10 and 12g, far too high. WHO/FAO recommends a daily intake of 5 grams per day to control blood pressure levels and reduce hypertension prevalence and related health risks in populations.
The UK’s Food Standards Agency (FSA) has set targets of 6 grams per day, and the new research appears to support the clinical relevance of such recommendations.
“Our present study provides further support for the current recommendations to reduce salt intake to less than 6 g/d in adults,” wrote the researchers, led by Dr Feng He from the Blood Pressure Unit at St. George's, University of London.
While previous studies have reported similar benefits, most of these have focused on white participants, with far fewer with people from other ethnic groups, explained the London-based researchers.
“The results in Asian participants (94 per cent were of South Asian origin) are of particular interest, as this is the first longer-term modest salt reduction trial in this group and demonstrates a clear benefit of salt reduction,” wrote He and his co-workers.
One hundred and sixty-nine people with untreated mildly raised blood pressure were recruited to take part in the study. They were randomly assigned to a low-salt arm or a placebo for six weeks. A subsequent washout period was followed by crossing over to the other arm. People from three different ethnic groups were involved, including 71 whites, 69 blacks and 29 Asians.
The low salt diet was associated with a reduction in sodium levels from 165 to 110 mmol over 24 hours. This salt reduction was associated with a “significant decrease in blood pressure from 146/91 to 141/88 mmHg,” said the researchers.
Furthermore, urinary albumin levels, a marker of kidney function, decreased from 10.2 to 9.1 mg/24-hour, indicating improvements in renal health.
“Our study, for the first time, provides evidence from a well-controlled randomised trial that a longer-term modest reduction in salt intake reduces urinary albumin excretion in white, black and Asian hypertensive individuals,” explained the researchers.
“Although the decrease in albumin excretion could be, at least in part, due to the reductions in BP, it is likely to have additional benefits on reducing both renal and cardiovascular disease above that which would be obtained from the BP falls alone.”
“These results, in conjunction with other evidence, suggest that a lower salt intake, in the long-term, could play an important role in the prevention of cardiovascular disease, renal disease and osteoporosis,” they concluded.
September 2009, Volume 54, Pages 482- 488
“Effect of modest salt reduction on blood pressure, urinary albumin and pulse wave velocity in white, black and Asian mild hypertensives”
Source: F.J. He, M. Marciniak, E. Visagie, N.D. Markandu, V. Anand, R.N. Dalton, G.A. MacGregor