Table of Contents

Introduction

Does everyone have to avoid salt?

What colour is your skin?

Who can benefit from dietary modification?

Is it worthwhile for everyone to eat less salt?

Potassium: an antidote for sodium?

Increase potassium intake or cut out sodium?

What is wrong with a single-minded anti- salt campaign?

Information about both sodium and potassium values is essential

Summary

Introduction

The New Zealand public has been bombarded with messages stating that we all need to reduce our intake of salt, that we are all getting too much dietary sodium. Is that really true for all of us? Is there no alternative? Monosodium chloride seems to be ready to join monosodium glutamate in the list of public food fears.

My interest was piqued when our local paper sneeringly wrote about teenagers who continued to eat salty French fries despite numerous health warnings. The possibility that they enjoyed the taste did not seem to be considered. In fact, I will show that the purported health risk from the salt content of French fries is probably mistaken.

What's wrong with salt? Salt is, of course, sodium chloride, and the culprit is the sodium ion (‘Na’ in scientific terminology). Excessive intake of sodium is said to cause:

• risk of high blood pressure

• risk of stroke

• risk of kidney damage

• risk of calcium loss, predisposing to osteoporosis

Does Everyone have to Avoid Salt?...

According to Jeffrey Steingarten's book, “The Man Who Ate Everything”, the majority of us do not suffer adverse effects from salt. Only people with high blood pressure (hypertension) might need to restrict their salt intake. In fact, only about one-third of hypertensives will benefit from such restriction. According to more recent studies, about one-third of people with normal blood pressure will be affected by high salt doses – say, two or three teaspoonfuls in one day – and these people too should limit their salt intake. That leaves two-thirds of us who do not need to restrict our enjoyment of that wonderful condiment, salt.

What about professional medical evidence regarding sodium? One of the main reviews cited by medical and nutritional agencies was published by He and MacGregor in 2002. Their review was based on a meta-analysis of published studies that satisfied strict requirements. The results were presented as shown in Fig. 1 (Abstract or Full article).

This graph deserves close study. Black dots are hypertensives (initial of 140/90 mm Hg or more) while white dots are normotensives (120/80). The size of each dot indicates the reliability for each study. The x-axis shows the how much sodium intake was lowered, while the y-axis indicates the change in blood pressure . The straight lines were forced through the 0,0 point (to the left of the vertical axis. Note that the y-axis seems to be located at x=1.2, whereas we expect it to signify x=0

For hypertensives, there seems to be a rough relationship: the more restriction of dietary salt, the larger the drop in blood pressure. On the other hand, a shallower line says that people who started with normal blood pressure showed much less benefit from salt restriction, with a disturbing amount of variability. (A famous biochemist once said, “drawing a straight line is an exercise in propaganda”.)

High blood pressure definitely puts a patient at high risk of stroke. If the relationship between improved blood pressure and sodium restriction is straightforward, then reducing the average salt intake by 3 g per day would prevent 40,000 strokes in the UK -- if the relationship is indeed linear.

Here is a photo-edited graph, with confusing artificial lines removed and a legitimate vertical axis at x=0. Surprisingly, there is no obvious difference between hypertensives and normotensives. Furthermore, these data look like a threshold response, with little or no benefit from eliminating 3 g salt per day. If that's correct, then mass elimination of a small amount of dietary salt will have no beneficial effect whatsoever. (Who said statistics don't matter?)

Since the average American consumption of salt is from 4 to 6 g a day, compared to a recommended intake of 1 to 2 g, those people who gave up 7 g salt a day must have been consuming astounding amounts of salt. Turning the He and MacGregor graph around suggests to me that people who consume more than 5 or 6 g salt are likely to show higher blood pressure. Does this mean that over-salting by 2 or 3 g a day is not dangerous?

In their 2002 review, He and Macgregor suggested that “the food industry should gradually reduce the salt concentration of all processed foods, which is not detectable by consumers, and continuing a sustained reduction over the course of the next decade ... a reduction in salt intake is the easiest change to make, because it can be done without the consumers' knowledge“. (Prof Macgregor informs me that this reduction in the UK is being done openly.) The validity of this approach assumes that small reductions in salt intake will cause significant drops in blood pressure across the entire population.

Sodium-restriction provides a maximum of 8 mm Hg reduction in systolic blood pressure for some hypertensives (systolic of 140 or more). For patients with severe hypertension, additional life-style and drug treatments may be needed.

Measurement of blood pressure is not precise. Just sitting up, compared to lying down, can make blood pressure jump by 5 mm Hg. A white-coated doctor will find higher values than his nurse. Monitors for home use are only accurate to ±3mm Hg. Anyone with normal blood pressure who wants to confirm that his or her heroic elimination of dietary salt has achieved the forecast 3-4 mm decrease will, therefore, have great difficulty.

At best, the campaign to obtain population-wide reduction in salt consumption might help public health authorities by reducing the annual incidence of stroke, but the benefit to individual normotensives will be unconfirmable. On the other hand, reducing public consumption of salt might lead to a real benefit in preventing or at least retarding the appearance of osteoporosis, although I’m not aware of any calculations in this regard.

What about people with high blood pressure? Many of them will not benefit from a low-sodium diet! Perhaps two-thirds of hypertensives are not salt-sensitive. (A DIY hypertensive could estimate his or her average blood pressure over several days, then carefully try a single small quantity of salt. If that causes higher blood pressure then a low-salt diet is indicated.)

What colour is your skin?

The likelihood of a hypertensive being salt sensitive is greatly affected by ancestry. In equatorial Africa, diet is notoriously low in salt, so most people have genes that lead to retention of salt. People living in areas away from the Equator have “defective” forms of these genes. In today’s salt-rich societies, the “defective” genes are better suited to survival! (Salt-retainers can show a significant blood pressure rise of 5 mm from just one g of salt.)

Recent work from the University of Chicago ) shows that people who evolved close to the equator often have genes for efficient salt-retention. Peoples further away from the equator, in cooler climates, have a “broken” form of this gene. The table below show percentages of each population with efficient salt-retaining genetics.

In many U.S. studies the majority of hypertensive subjects are black, because black Americans are more likely to have hypertension than are whites. Blacks are also far more likely to be salt-sensitive than whites. Compounding this is likely to be a diet poorer in fruits and vegetables (Morris et al. 1999) :

(Onwuanyi et al., Hypertension 1998:31:1070-1076)

In New Zealand, what percentage of Polynesians is salt-sensitive? What about Asian immigrants? Indians? Since salt-sensitive people need to avoid excess salt, some non-PC research could determine where health education should be focussed. If salt-reduced foods are to be legal requirements, should enforcement be particularly strict for shops in black neighbourhoods?

Who can benefit from dietary modification?

The DASH-Sodium study was an important large-scale investigation. (DASH stands for Dietary Approaches to Solving Hypertension) The motivation was, in part, to test the observation that vegetarians are less likely to be hypertensive.

There were two forms of the DASH diet, one emphasizing more fruits and vegetables, the other adding two servings a day of low-fat dairy products. The control group ate a “typical American diet”. The first table below shows servings per day for each diet

The participants were 58% black and 41% hypertensive, but skin-colour was disregarded when the results were analysed! Overall, the full DASH diet of fruits, vegetables and dairy caused significant drop in blood pressure in just a few weeks. Eventually, the authors admitted that certain subgroups responded best to salt-reduced diets: hypertensives, older subjects, and those ”of African-American ethnicity” (M H Weinberger, Hypertension 2004:44:609).

A second DASH study compared the control diet with the DASH diet, at three different levels of salt intake. The results showed that simply increasing fruit/vegetable/dairy intake led to a useful drop in blood pressure even when salt intake was not changed! The figure below is taken from a pamphlet prepared by the Medical Research Council Human Nutrition Research,Cambridge.

Anti-salt campaigners often disregard this result, so that official propaganda implies that the only way to lower blood pressure is by a major reduction in salt intake. That approach is generally impractical for laymen, faced with high- salt commercial foods. It was possible in the SALT study only because the subjects ate hospital-prepared foods. Which is easier:-- adding fruits and vegetables to a diet, or switching entirely to a limited set of commercial low-salt foods?

Is it worthwhile for everyone to eat less salt?

The argument for universal salt reduction is predicated in blind faith that the relationship between salt and blood pressure fits a straight line applying to the whole population. It assumes that a hypothetical reduction of 1 or 2 mm systolic pressure has real consequences. Whether population-wide salt reduction has any effect on death rates has never been confirmed!

The highly respected Cochran Coalition wrote: “The magnitude of the effect in Caucasians with normal blood pressure does not warrant a general recommendation to reduce sodium intake.”

“Intensive interventions, unsuited to primary care or population prevention programmes, provide only minimal reductions in blood pressure during long-term trials. Further evaluations to assess effects on morbidity and mortality outcomes are needed for populations as a whole and for patients with elevated blood pressure.” (http://www.cochrane.org/reviews/en/ab004022.html)

On the other hand, for people with hypertension, the Cochrane panel concluded that “Reduced sodium intake in Caucasians with elevated blood pressure has a useful effect to reduce blood pressure in the short-term… Evidence from a large and small trial showed that a low sodium diet helps in maintenance of lower blood pressure following withdrawal of antihypertensives. If this is confirmed, with no increase in cardiovascular events, then targeting of comprehensive dietary and behavioural programmes in patients with elevated requiring drug treatment would be justified. {http://www.cochrane.org/reviews/en/ab003656.html}

In 1996, another team of epidemiologists wrote, “Data linking baseline sodium to mortality and morbidity outcomes are sparse, with only six known studies. Of these, two showed no association, two showed an inverse association, and two showed a direct association only in obese subsets. No studies have examined outcomes after sodium reduction, and no studies have linked sodium to outcomes or even a blood pressure benefit among treated hypertensives. Universal recommendations for sodium reduction or dietary sodium goals should await evidence that such interventions are both safe and effective as measured by morbidity and mortality outcomes.”(Cohen and Alderman, 1999)

Potassium: an Antidote for Sodium?

Increasing intake of potassium (‘K’) can go a long way to reversing or preventing adverse effects of sodium. Our ancestors evolved with a diet high in potassium (from fruits and vegetables), but low in sodium. Potassium is typically concentrated inside our cells, whereas sodium is excluded from cells and pushed out into extracellular fluid. Maintenance of this situation is so important that ten or twenty per cent of our basal metabolism is devoted to fighting the tendency of these ions to equilibrate.

High intake of potassium can alleviate deleterious effects of sodium on blood pressure, kidney function, and calcium loss. One example is shown in the work by
Morris et al. 1999 . [N.B. These figures are my estimates from the published bar-graphs. This was a small-scale experiment so numbers are only approximations.]

The 38 healthy, non-hypertensive subjects were kept on a low-potassium diet for 4 weeks, then challenged with 2-1/2 tsp salt each day. More than twice as many blacks as whites showed higher blood pressure from that challenge. The average change in blood pressure of the whites was also much less. (This average apparently included both responders and non-responders.)

For the last 3 weeks, the participants continued to get a high-sodium diet, but were also given either 70 or 120 mmol potassium bicarbonate capsules. At 70 mmol potassium a day, fewer whites were sensitive to salt, and their mean b.p. response was trivial. At 120 mmol potassium, only 20% of the black subjects still responded to salt. (No whites were tested at 120 mmol K.)

The conclusion was that, to prevent salt-induced blood pressure rise, black subjects require higher intakes of potassium.

Since fruit and vegetables are the main dietary sources of potassium, and since black populations in the U.S. tend to have lower consumption of these, black Americans are doubly at risk.

The DASH study results confirm the benefits of more dietary potassium. When more fruits and vegetables were eaten, potassium intake more than doubled, to 4.7 g/day. Higher intake of potassium, by eating more fruits, vegetables and dairy, strongly reduced hypertension even without any change in sodium intake. Dietary Approaches to Prevent and Treat Hypertension. Hypertension. 2006;47:296

Other studies at the University of California) have suggested that improved potassium nutrition can prevent salt-induced loss of calcium from the bones of post-menopausal women.

Increase Potassium Intake or Cut out Sodium?

Since 75-80% of our salt intake comes from processed foods, it is probably much easier to eat more vegetables while striving for a modest reduction of sodium intake.

Just choosing vegetables at random, however, may not be an efficient way to increase our dietary potassium. Here is a link to a useful table of potassium in food, courtesy of the Auckland (NZ) District Health Board: Potassium content of typical foods . (The low potassium value for "spinach" applies to "NZ spinach", a different plant from ordinary high-potassium spinach.)

Given two food products with similar sodium levels, the logical thing to do is to choose the product with the most potassium. Unfortunately, you won't find this information on most food labels. Some notable exceptions are certain juices, which clearly point out that they have far more K than Na.

As a general rule-of-thumb, you can count on 0.2 – 0.3 g potassium in every 100 g of most fruits and vegetables. Some are higher, e.g., bananas have 0.4 g/100g. Silver beets have 1.3 g per 100 grams! Potatoes have about 1 g K per 100g, and even fast-food French fries have more K than Na! (Check www.dole5aday.com or the USDA website for extensive tables.)

In New Zealand and Australia, official recommendations are 3.8 g K/day for men, 2.8 g/day for women. In the U.S., however, all adults are told to consume 4.7 g K/day. Since these numbers are only estimates, we need only remember 3 g for kiwi women, 4 g for kiwi men, and 5 g for Yanks. As the Australian Heart Foundation quaintly puts it, “those who wish to prevent chronic disease (inc. cardiovascular disease)” should aim for 4.7 g K, while everyone else (who isn't concerned with chronic disease?) can get away with less than 4 g.

A simple rule of thumb is to try for a K-to-Na ratio of at least 2, although some authors recommend ratios of 3 or 4.

Thinking about potassium seems to inactivate all critical faculties. How else explain recommendations for "4700 mg" of potassium? If you believe this hyperdigitised pseudo-scientific figure, then someone consuming only 4698 mg of potassium is deficient! (Please read my recent article about How food labels mislead us, which will open in a separate window.) Forget the unjustified decimal points, just aim for about 5 grams of potassium a day. Alternatively, try to ingest twice as much potassium as sodium.

Our inadequate labelling laws make it difficult to be a knowledgeable consumer of high-potassium foods. Most food products list sodium content (required by law)but not potassium. I reiterate, we cannot make an informed decision on what foods to choose unless we have know both sodium and potassium analyses. As an example, recently I was looking at several snack items in an Australian shop; each of them had roughly half a gram (500 mg) sodium per 100 g. But one product (corn chips) had very little potassium. On the other hand, one potato chip product had over 1200 mg (1.2 g) of potassium. That's a potassium/sodium ratio well above my target of "2". Thanks to the comprehensive labels of the Australian food companies, I was able to choose an enjoyable snack that enhanced my daily potassium quota.

Health food “potassium supplements” are not allowed to contain more than 99 mg K, that is, two dozen pills a day (added to our normal diet) will provide the desired 5 g K. On the other hand, supermarkets sell “Low-Salt” products with about 2/3 potassium chloride and 1/3 sodium chloride. One warning: potassium is rather bitter, so high-K salt has to be used with care. Also "natural" potassium from vegetables and fruits comes as organic salts, whereas the chloride of potassium may not be as beneficial.

Another warning: people with very severe kidney disease cannot handle potassium salt. (They cannot handle sodium salt either.) Since certain medicines can interfere with potassium excretion, it's probably a good idea to check with your physician before any major diet change.

High levels of sodium can increase urinary excretion of calcium, especially in post-menoopausal women. Potassium bicarbonate, potassium gluconate, and similar additives can reverse this effect of sodium, but potassium chloride is not beneficial for slowing osteoporosis.

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What is wrong with a single- minded anti-salt campaign?

Teaching school children to pick foods with the lowest amount of sodium is a thoughtless and misleading approach to nutrition. Valuable foods with moderate amounts of sodium would be rejected by this simple-minded sodium mentality. In the UK, when authorities banned salt-cellars from school cafeterias, consumption of vegetables dropped by a worrying amount, because vegetables need salt to mask their slight bitterness.

Iodine is essential for brain development of unborn children, yet New Zealanders are consuming less and less iodine in our diet. That brain damage cannot be reversed by better nutrition after birth. Iodised salt is the obvious route to prevent cretinism and goitre. However health groups are afraid to recommend use of iodised salt, since that would be interpreted as supporting continued high levels of salt intake, a totally non-PC attitude in the present climate of anti-sodium hysteria.

The anti-salt campaign sets us up for feelings of guilt and inadequacy. Our biology is such that salt has taste appeal, so we feel worthless when we enjoy a bag of potato crisps. (I don’t refer to over-salted items, which are as unpleasant as any other over-seasoned food.) Worrying about a little bit of salt added to the vegetables is pointless when most of our dietary salt comes from commercially processed foods.

Information about both sodium and potassium values is essential for informed food choices.

Data are from the USDA Database . Note that the reconstituted potato snacks have much less potassium than potato chips, yet both have the same amount of sodium. Potato sticks are actually rich in potassium, but unfortunately are also rich in fat.

For general info about K content of many foods, try this excellent table from the Auckland District Health Board: Potassium Contents of NZ Foods (Warning: the low potassium value for "spinach" refers to a different plant, "New Zealand spinach". True spinach is an excellent source of potassium.)

Summary:

Excess intake of salt can lead to problems of blood pressure, kidney function, stroke, and calcium loss. To a large extent, increasing potassium intake even without changing sodium consumption can alleviate these problems. Adding more fruits and vegetables to the diet is an easy way to increase potassium intake.

There is little evidence to suggest that healthy individuals with low blood pressure and no renal disease will benefit from sodium restriction. In fact, many people with high blood pressure show no response to salt restriction.

Calcium loss from bones is accelerated by high intake of sodium, and retarded by high levels of potassium. Diets with more K and less Na should therefore lower the risk of osteoporosis.