Response to the Salt Manufacturers’ Association complaint to the
20th September
Professor Graham MacGregor, Chairman of CASH and Professor of Cardiovascular Medicine at St George’s Hospital, London today said: “I am not surprised that the Salt Manufacturers Association is opposing all moves to reduce salt consumption – their job is to sell salt. Approximately 40% of their members’ profit comes from sales of salt to the processed food industry so they are fighting to maintain their profitability. Unfortunately for them, however, the evidence linking our current salt intake to blood pressure levels is very strong, and bringing our salt intake down to below the recommended level of 6g per day for adults will result in many thousands of lives saved in years to come.”
Evidence linking our current salt intake to blood pressure levels:
An expert Committee drawn up by the Department of Health first recommended a reduction in salt intake from an average intake of 9 grams/day to 6 grams/day in adults in 1994. Last year (May 2003) the expert committee for the Food Standards Agency (SACN) reported all the evidence linking salt to blood pressure, after having spent over a year looking at all the research. SACN concluded that the evidence was much stronger than in 1994 and set a similar target for all adults to reduce salt intake to 6 grams/day and for the first time set much lower targets for children. Importantly, salt intake over this period of time has increased from an average of 9 grams/day to at least 10.5 grams/day. (www.sacn.gov.uk)
The evidence linking salt intake to blood pressure is based on six different types of evidence.
Animal evidence – chimpanzees, our nearest close relative, have blood pressures on their normal diet of less than 100/70 mmHg. However, when fed the same amount of salt as we currently consume, ie 10 to 15 grams/day, their blood pressure rose dramatically. (Denton et al, 1995). Yamomamo Indians, who live in the Venezuelan jungle and eat an evolutionary diet with no access to salt have an average adult male blood pressure of 92/63 mmHg. These blood pressures are very similar to those found in chimpanzees, gorillas and orang-utans on their natural diet.
All other animal models of high blood pressure have to be given a high salt intake in order for the blood pressure to increase. (Macgregor and de Warderner,1998)
Epidemiological studies, which study different communities, show that those with higher salt intakes have higher blood pressures. A large international InterSalt study with 52 different centres throughout the world showed a close relationship between salt intake and the rise in blood pressure with age. (Intersalt, 1988)
Migration studies that have followed tribes migrating from a low salt to a high salt environment have documented the increase in blood pressure that occurs on migration. (Poulter et al, 1990)
Intervention studies – a study in Portugal of two different villages, where one village was given advice on how to cut their salt intake and given processed foods containing less salt against a village with identical measurements of blood pressure who ate a higher salt diet. This showed a progressive difference in blood pressure after one and two years study and this clearly demonstrated that reducing salt intake in a community reduces blood pressure. (Forte et al, 1989)
Genetic studies – all the rare causes of high blood pressure in man due to genetic mutations result in salt retention. All genetic causes of low blood pressure are due to salt loss. (Lifton, 1996)
Treatment trials – there have been numerous studies on the effect of reducing salt intake on blood pressure. These demonstrate that, both in people with high blood pressure and also in people with normal blood pressure, reducing salt intake for one month or more causes a fall in blood pressure which would cause major reductions in deaths and disability from strokes and heart attacks. From an analysis of all these studies, it has been shown that a 6 gram/day reduction in salt intake would cause a 24% reduction in stroke deaths and an 18% reduction in heart attacks. In the UK this equates to 70,000 strokes and heart attacks each year – 35,000 of which are fatal. Even a 10% reduction in salt intake, which could easily be achieved, would lead to a reduction of approximately 12,000 strokes and heart attacks, 6,000 of which are fatal. (He and Macgregor, 2003)
References
1. Denton D, Weisinger R, Mundy NI, Wickings EJ, Dixson A, Moisson P, Pingard AM, Shade R, Carey D, Ardaillou R, Paillard F, Chapman J, Thillet J, Michel JB. The effect of increased salt intake on blood pressure of chimpanzees. Nature Medicine. 1995; 1:1009-16.
2. Forte JG, Pereira Miguel JM, Pereira Miguel MJ, de Padua F, Rose G. Salt and blood pressure: a community trial. J Human Hypertens. 1989;3:179-84.
3. He FJ, Macgregor GA. How far should salt intake be reduced? Hypertension 2003; 42: 1093-9
Intersalt cooperative research group (1988). Intersalt: an international study of electrolyte excretion and blood pressure. Results from 24-hour urinary sodium and potassium excretion. BMJ 297: 319-328
4. Lifton RP. Molecular genetics of human blood pressure variations. Science. 1996;272:676-80.
5. Macgregor GA & de Wardener HE (1998). Salt, Diet and Health (eds MacGregor G and de Warderner HE) Cambridge University Press.
6. Poulter N, Khaw KT, Hopwood BEC, Mugambi M, Peart WS, Rose G, Sever PS. The Kenyan Luo migration study: observations on the initiation of a rise in blood pressure. BMJ. 1990;300:967-72.
