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Salt — beware of that other passive consumption threat to people’s health

Salt Awareness Week takes place from 11 to 17 March 2013. In this article, Bob Michell writes that we generally eat too much salt, usually through no fault of our own

By Bob Michell

Salt Awareness Week takes place from 11 to 17 March 2013. In this article, Bob Michell writes that we generally eat too much salt, usually through no fault of our own

The most prevalent, long-established and, arguably, one of the most harmful food additives has no E-number. Other sodium compounds do, but not sodium chloride — common salt.

Moreover, in industrialised countries it is a more pernicious hazard than tobacco; it is obvious when people are smoking, and restrictions in public places have reduced the risks from passive smoking. Anyone can spot a covert smoker in a café, but not the salt hidden in their food. For most people, the majority of their salt intake is not the result of their choice, in the kitchen or at the table, but is the result of the salt added by those who process food — it is passive sodium intake.

How little do we need ?

Does it matter? Is salt harmful? Are there proven risks? Despite the sand scattered in politicians’ eyes by industrial interests dependent on salt (including its undoubted capacity to increase how much we drink) to suggest that doubts remain, the evidence that high salt intake predisposes populations to hypertension and strokes is far stronger than the underpinnings of much modern medicine. Moreover the consequences are not simply individual, but national. At a time when urgent questions surround what is affordable for the NHS, millions of pounds are consumed by the costs of treating hypertension and its consequences. Although this is the most important and best documented adverse effect of excess salt intake, there are others. Do we need all this salt? Unquestionably not, with rare exceptions.

It is unlikely that adult mammals have a daily sodium requirement above 0.6mmol/kg.1 So a 75kg adult needs a maximum of 4g/day (1mmol = 58.5mg NaCl, 23mg Na). They probably need far less. Palaeolithic diets probably provided 0.4mmol/kg/day and data from Yanomami women in the South American rainforest and from sheep suggest that even pregnancy and lactation are sustainable on 0.1mmol/kg/day — as little as 0.4g daily. A serving of breakfast cereal can easily double that, even without the milk. These are maintenance requirements; pregnancy and lactation create additional demands (as do conditions such as acute diarrhoea or adrenal insufficiency).

RPS advice

The Royal Pharmaceutical Society supports Consensus Action on Salt & Health (CASH) and would encourage pharmacists to get involved in the campaign for salt awareness. Patients with long-ter m conditions such as hypertension, diabetes and asthma, should pay particular attention to their daily salt intake, and pharmacists can play an important part in helping patients moderate this.

Pharmacists are recognised to have a key public health role and should take the opportunity to provide health information to patients about the dangers of high salt intake, the benefits of reducing consumption and also advise on practical measures on how to do this. Opportunities may arise when offering healthy living advice, counselling patients when supplying medicines, as part of medicine use reviews or the new medicines service (in England), discharge medicines reviews (in Wales) or chronic medication service (in Scotland). 

The Society has many resources which discuss conditions where a reduction in salt intake is beneficial. A full range of RPS resources can be found at www.rpharms.com.

 

Objective or subjective?

It is important to emphasise that there is a physiologically calculable, objective requirement for sodium because, unlike the animal nutrition literature, human discourse routinely espouses arbitrary concepts of “low”, “high” or “customary” intake. Thus papers purporting to compare low and high intake often simply compare different levels of excess, as did a publication in JAMA,2 which claimed that higher salt intakes were healthier, but dealt with intakes of 1.5, 2.4 and 3.7mmol/kg/day, three to seven times actual requirement; there were no low intakes. (It is as if we claimed that high speeds were safer in urban areas based on comparisons between 90–220mph rather than a baseline of 30mph. There might indeed be fewer accidents at 220mph because these could well be the most skilful drivers.) In fact, there were technical errors within the study which raised serious doubts about the data.

Those who would argue that humans need more salt than other mammals must demonstrate what unique defect in their renal, colonic or dermal response to increased aldosterone secretion creates this additional requirement. The exception would be among humans as yet unacclimatised to high temperatures and high humidity but experiencing heavy exertion. Even then, excess sodium intake will delay or prevent aldosterone-induced adaptive minimisation of sodium concentrations in sweat.

The most compelling evidence regarding salt and hypertension is the fact that there is no known exception to the observation that those few human populations whose routine sodium intake is close to their nutritional requirement rather than far above, do not show the age-related rise in blood pressure which is regarded as “normal”, even by insurance companies.1 Pet dogs, which have high routine sodium intakes, also show an age-related rise in blood pressure although, as a species, canines seldom show essential (ie, primary) hypertension.3 Granted that the concept of a defining “threshold” of systolic or diastolic pressure is no longer tenable and higher pressures are associated with increased risks even within the “normotensive” range,4 the ideal population salt intake should not exceed that at which arterial pressure remains stable with age. The slope of the age-related rise in blood pressure will probably decide whether we end up on antihypertensive medicines or, worse, whether we suffer cardiovascular damage, including strokes. Excess salt intake costs the NHS millions, perhaps billions if the data are sufficiently sensitive.

How much can we tolerate ?

People vary: not all heavy smokers die young, but as a population trend the link with premature death is inescapable. There are high-salt populations without the expected high prevalence of hypertension, but very few; low-salt populations with hypertension are yet to be found. Moroeover while hypertension remains the main hazard of routine consumption of excess salt, it is not the only adverse effect.1 Excretion of excess sodium also increases calcium excretion to a degree that can harmfully reduce bone calcium. Although Helicobacter pylori is the primary cause of gastric cancer, excess dietary salt is a predisposing factor.

Agenda for progress

An application to class sodium chloride as a new food additive would almost certainly fail. Chain salt consumption is as addictive and harmful and far more prevalent than chain smoking ever was. Over 25 years ago, the World Health Organization recommended that daily salt consumption should be less than 5g, but that is still around 1.1mmol/kg, ie, 10 times the likely requirement.
The National Institute for Health and Clinical Excellence recommends cutting average daily UK salt intake to a level equivalent to 0.7mmol/kg by 2025, anticipating an associated reduction of 10 per cent in coronaries and 13 per cent in strokes. A recent paper in the BMJ concluded that “the question is not whether to reduce salt intake but how”.5 Efforts involving several groups, including the Food Standards Agency, previous governments, some food manufacturers and several supermarkets, together with expert advice from informed clinical advocacy groups such as CASH (Consensus Action on Salt & Health) have already achieved an encouraging but inadequate reduction in national salt intake. It remains above target and the target remains far above our nutritional need for sodium.

Anything that health professionals can do to reduce unnecessary salt consumption will reduce the national cost of cardiovascular disease. In turn, this will protect funds available for unavoidable diseases. Reduction of dietary salt intake is now a priority for the EU and the United Nations.6 It is time for pharmacists, the trusted scientists in the high street who are already involved in promoting various activities to sustain healthy living, to become the accessible source of expert advice on moderating dietary salt intake.

National salt awareness week

National Salt Awareness Week takes place from 11 to 17 March 2013. The theme of the campaign is “Less salt please” and it aims to show how people can use less salt and still have flavourful food.

The campaign will highlight how it is difficult to eat less salt when eating food prepared by other people in restaurants, take-away outlets and fast food venues. “These foods can contain a lot of hidden salt and, without labels on these products, it is very hard to make a healthier choice,” says CASH (Consensus Action on Salt & Health), which is running the campaign.

Given pharmacists’ role in health promotion, they may be interested in supporting this campaign, and CASH has a variety of posters, leaflets and fact sheets that they can order or download from the CASH website (www.actiononsalt.org.uk). Orders for printed materials must be placed via the website no later than 16 February 2013. — Graeme Smith

 
Bob Michell is a veterinary surgeon who has had a long association with the Royal Pharmaceutical Society, having been a member of the regulatory RPSGB Council for many years up until 2010

 

References

1 Michell AR. Comparative aspects of salt and hypertension. In: The Clinical Biology of Sodium. Oxford: Pergamon, 1995, pp123–54.
2 Stolarz-Skrzypek K, Kuznetsova T, Thijs L et al. Fatal and nonfatal outcomes, incidence of hypertension and blood pressure changes in relation to urinary sodium excretion. JAMA 2011;305:1777–85.
3 Michell AR. Hypertension in dogs: The value of comparative medicine. Journal of the Royal Society of Medicine 2000;93:451–2.
4 Ramachandran SV, Larson MG, Leip EP et al. Impact of high-normal blood pressure on the risk of cardiovascular disease. New England Journal of Medicine 2011;345:1291–7.
5 Cappuccio FR, Capewell S, Lincoln P, et al. Policy options to reduce population salt intake. BMJ 2011;343:d4995.
6 Implementation of the EU Salt Reduction Framework: results of member states survey. Publications Office of the European Union, 2012.

 

Citation: The Pharmaceutical Journal DOI: 10.1211/PJ.2013.11115977

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