A study from McMaster University in Canada suggests that it is possible to double our daily salt limit. It would, therefore, go from 6g per day to 12.5.
1 The maximum daily intake of salt of 6 g is therefore considered today as too low and even dangerous for health. What are the risks of too low salt intake?
The idea that the more salt one eats the more one is hypertensive is wrong. It is part of a number of ideas that constitute the vademecum of false science. Florilège: eggs, oysters raise cholesterol, saturated fats give infarction, salt raises tension, fat makes you fat, the brain needs sugar, alcohol is good for the heart, meat gives the colon cancer, the fish is full of mercury ... Emotionally, defensively or lazily by activating our fast brain we give more importance to these slogans than to more complex ideas. Those who repeat this truncated information know it well ...
With regard to salt and blood pressure, it is fairly well established by epidemiology, there is a J curve between salt/sodium consumption and mortality and/or serious cardiovascular events (stroke, myocardial infarction). In the PURE epidemiological study to which you refer (https://www.nejm.org/doi/full/10.1056/NEJMoa1311889) it was found that low salt intake was associated with increased risk mortality and risk of cardiovascular events (Figure N ° 1). According to these data, it is risky to consume little salt and in any case less than 11.9 g / d
Two remarks to use in practice this observation: first everything depends on the shape of the J and its point of inflexion (low point of the risk that can guide the nutritional recommendations). The consumption associated with the lowest risk is 4.72 g / day of sodium, ie 11.8 g / day of salt. On these data and if we stick to a supposed causality, it would be riskier to cut its consumption of salt by two (from 4.72 to 2.36 g / d of sodium or from 11.8 to 6.9 g / day of salt) than doubling it. The risk of all-cause mortality and cardiovascular events is greater if one halves its salt intake. Secondly, no single nutrient can be singled out as the optimal diet is a set of several thousand molecules that contribute to health. Salt is not bad in itself but is vital and its contributions cannot be dissociated from other minerals especially potassium. It is essential to think in terms of the relationship between minerals. For example, it is well established that those who consume a lot of salt and are hypertensive also have very low potassium intake ...
Figure N ° 1.
Association of estimated 24-hour sodium excretion with the risk of death and major cardiovascular events.
Panel A shows the association curve between 24-hour urinary sodium excretion and the composite outcome of death by cause and major cardiovascular event. The curve is truncated at 12.00 g per day (event rate in participants with sodium excretion> 12.00 g per day, 8 events in 305 participants). Panel B shows a graph restricted to the curve of the association between estimated sodium excretion and the death of any cause. The event rate in participants with sodium excretion of more than 12.00 g per day was 5 events in 305 participants. Panel C presents a graph restricted to the association between estimated sodium excretion and major cardiovascular events (defined as deaths from cardiovascular causes, myocardial infarction, stroke or heart failure). The event rate in participants with sodium excretion of more than 12.00 g per day was 6 events in 305 participants. All points were adjusted for age, gender, geographic region, level of education, alcohol consumption, body mass index and diabetes mellitus, history of cardiovascular events and current smoking. The dashed lines indicate 95% confidence intervals. The median sodium excretion (4.72 g per day) was the reference standard, indicated by the red line. To convert the estimated sodium excretion values into salt intake in grams per day, multiply by 2.5.
2 This epidemiological study is based on sodium concentrations of approximately 95,000 people in 21 countries. But are we all equal in the face of salt consumption? Does genetics not take into account?
The PURE study on sodium is an observational study Observational studies, interesting as they are, remain very difficult to interpret. Despite the significant progress made in measuring physiological, human metabolic parameters there is still a great deal of uncertainty on these issues, particularly in dietary studies. Second, the causal relationship between results and presumed factors in the diet or other determinants is highly controversial. We can only take these data to detect tracks for interventional studies where the regime is perfectly controlled and where one group is compared in real time to another group. This should be remembered each time we comment on an epidemiological study. At the same time, it should be emphasized that if an epidemiological study concerns 95000 people it is at the same time a considerable number of data and an average vision that can easily erase particularities.
Salt sensitivity describes the fact that some populations or individuals may be at increased risk for cardiovascular events associated with salt intake. Clinically there is a marked heterogeneity of blood pressure variations in response to salt/sodium reduction. Ethnicity, hypertensive status and obesity modify the association between sodium consumption and cardiovascular diseases (or blood pressure), but these studies are far from univocal. The genetic basis of salt sensitivity and their direct association with specific genetic polymorphisms of hypertension are not known. The inter-regional differences in the association between sodium consumption and CV risk cannot be interpreted without these genetic bases. We are clearly in a zone of very inadequate knowledge but it is likely that these differences exist because of disparities in the availability of salt throughout the history of the different populations of the globe. The practical conclusion is to personalize the advice both according to the differences observed between the ethnic groups (the Asians show in the studies a greater sensitivity to the salt than the other populations) and also according to the individuals.
3 What are the risks of encouraging people to consume more salt (especially because of the limited sodium consumption)?
The most important thing is not to measure the amount of salt that is ingested. In fact, no one does it either patients, doctors or dieticians except in studies. But given the inaccuracy of the meal questionnaires, the authors of the PURE study chose to measure the excretion of sodium (and not salt) in the urine.
The important thing is to know what we are talking about. Table salt is almost exclusively sodium chloride. The differences between the different salts are firstly the water content and marginally differences in the small content of sodium chloride for the benefit of some micronutrients such as iron, calcium, magnesium, potassium or zinc. There is minimal variation in its sodium chloride content depending on the origin, rock salt, sea salt ... The sea salt contains other minerals in infinitesimal quantities (Table 1).
Mineral
|
Unit
|
Content in 100g of refined table salt
|
Content in 100g of raw sea salt
|
Calcium, Ca
|
mg
|
3
|
17
|
Iron, Fe
|
mg
|
0.33
|
0.14
|
Magnesium, Mg
|
mg
|
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|
0.14
|
Phosphore, P
|
mg
|
0
|
0
|
Potassium, K
|
mg
|
8
|
30
|
Sodium, Na
|
mg
|
39100
|
33800
|
Zinc, Zn
|
mg
|
0.10
|
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|
Table N ° 1
Comparison of refined salt and raw salt (https://ndb.nal.usda.gov/ndb/foods/show/02047?fgcd=&manu=&format=&count=&max=25&offset=&sort=default&order=asc&qlookup=table+salt&ds=&qt=&qp=&qa=&qn=&q=&ing= ) and (https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1745-459X.2010.00317.x ).
In no way is it advising the population to eat more salt. No dietary advice makes sense when it comes to recommending an isolated nutrient because no one is able to count the nutrient in the purchased foods during the day. The real question is: where does sodium chloride come from?
(https://pdfs.semanticscholar.org/2fba/52be173c3c8b610de9313ceb4119d6d055a3.pdf ), (Figure N ° 2).
The appropriate answer is to advise foods, not nutrients, minerals and in this case salt or products or even more supplements! This is why the main advice is to avoid the majority of industrial products because they are salty and sweet. In addition, they are often processed by refining or cooking at high temperature and therefore poor in micronutrients while becoming dense in calories. These products are the source of about 70% of the salt consumed which is considerable (Figure No. 2). In this regard it must be emphasized that it is not the salt content of this or that product that matters is the origin of the majority of salt consumed. Clearly, there is no need to focus on anchovies while all bakery products come first for the amount of salt consumed ...
"Main foods vectors
Given our eating habits, most of the salt consumed comes in France first bread and rusks, then cold cuts, condiments and sauces, cooked dishes, cheeses, soups and soups, as well as quiches and pizzas. "
https://www.anses.fr/fr/content/le-sel
But there is more; industrial products create a crowding-out effect on the consumption of fresh foods, particularly plants rich in potassium (leaves, bulbs, flowers, fruits ...). Avoiding industrial products and consuming fresh produce decreases the amount of salt, increases potassium intakes, and other benefits associated with whole foods that are little or not processed. While using the table salt shaker for the pleasure of food and satiety. Unfortunately, I see too often people who eat products all year long and who believe to meet the recommendations by using parsimoniously the salt cellar at the table. It's just the opposite that must be done.
Figure N ° 2
The proportion of total sodium intake from various sources among US residents (Birmingham, Palo Alto and St. Paul) (n = 450).
https://www.ahajournals.org/doi/abs/10.1161/circulationaha.116.024446
After this very basic general remark, we must speak of particular situations. Depending on your ethnic background, your family or personal history, your current cardiovascular status, it may be appropriate or not to reduce your salt intake. If this is the case, think of being effective: 70% of the salt comes from industrial products.
As in other fields, science is shaking up beliefs based on low-quality or even truncated studies. Salim Yusuf is a cardiologist who dares to question dogmas from experimental and clinical data, with the aim of improving the health of patients. For salt, it is necessary to be discriminating and to avoid the too easy "less is more".
"It is very hard to get sodium to the levels of people talking about-2.3 g or lower. And we show that practically, no one in the world is down to that level. So we are making recommendations that most people, 99% of the world, can not follow. From a practical point of view it makes no sense and from a scientific point of view, it makes no sense. "
Salim Yusuf
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