Could it be true? Are we eating too much salt? Is a lot of salt dangerous or beneficial?
There is no doubt that salt is necessary for the human body to function. The sodium cation and the chloride anion (the two ions forming sodium chloride which is the chemical name of table salt), are major electrolytes in the body, sodium being the main electrolyte in the extracellular environment.[1] First of all, sodium regulates the volume of liquids in the body and contributes to the maintenance of its acid-base balance. Secondly, sodium plays a key role in sending nervous impulses throughout the whole body and in muscular contraction. Thirdly, the absorption of certain carbohydrates, mainly glucose, into the body is possible through mechanisms which are sodium-dependent.
On the other hand, the lack of a sufficient sodium quantity in the blood attracts serious symptoms like muscular and abdominal cramps, vomiting, weakness, fatigue, headaches, disorientation, lethargy and even convulsions and coma.[2] The symptoms of this deficiency, which in medical terms is called hyponatremia[3], indicate the essential role played by sodium in the human body and indirectly, the importance of table salt.
Salt is truly good. But can we have too much of a good thing? To answer this question, we should first define salt excess.
Surprising connections in the history of salt
People have appreciated, since ancient times, the value of salt for one’s diet and health. “Is tasteless food eaten without salt?” asked an old biblical character (Job 6:6), and Plutarch described it as “the most noble of all foods, the best of spices”.[4] Another biblical expression, “the salt of the earth”, is still utilised in some cultures to point to a person who is worthy of admiration.[5] Another word we use without thinking of its etymology comes from an old term used in relation to salt. The payment that the Roman soldiers received and used to buy salt was called salarium, a term whose meaning was later transferred to the payment of civilians—salary. (Another theory, based on a fragment from Pliny, says that, long ago, soldiers were actually paid in salt). In the sixth century, Isidore of Seville wrote that “Nothing is more necessary than salt and sun”.[6]
Is it even possible to define salt excess?
The critics of prudence when it comes to the use of salt believe it is impossible to define salt excess, saying that there is a huge margin of error due to the age and body weight differences between consumers. In reality, adequate values of salt intake have been defined long ago, according to age groups and genders, in different countries, with some small differences from one country to another.
For instance, in the United States, for children up to 6 months old, the recommended sodium intake[7] is established at 120 mg/day[8]. For children between 6 months and 1 year old, 370 mg/day. From 1 to 3 years of age, the recommended amount is 1000 mg, from 4 to 8 years 1200 mg, and from 9 years to the age of 50 (including pregnant women and nursing mothers), 1500 mg. After the age of 50, when the kidney function starts to diminish, the recommended sodium dose is reduced to 1300 mg, and after 70 years old, to 1200 mg.
In the United States, the distinction is made between “adequate intake” (AI) and the “tolerable upper intake level” (UL). In the US, the tolerable upper intake level is 2300 mg. In the United Kingdom too (as in many other countries in the world) one can find maximum recommended quantities for different age groups. Here, the official recommendations are limited to a maximum recommended quantity, which for 11 years old and over is 2400 mg of table salt (6 grams of sodium) per day.[9]
Why avoid excessive salt intake?
The beneficial or toxic effect of any substance depends on the dose (in Paracelsus’ words: sola dosa facet venenum), and salt is no exception. In lab experiments, the dose which causes 50% mortality rate (DL50) is 3g/kg for a rat and 4g/kg for a mouse.[10] Extrapolating this for humans (because, luckily, not even dictators dared to determine the lethal dose by performing experiments on humans), it can be reasonably presumed that a dose of approximately 200 grams of salt can be lethal for an adult (with a 50% probability). It’s unlikely, however, that someone would willingly swallow a cup of salt.
Problems occur with chronic consumption of much lower doses, but large enough to affect our health. The main negative effects are reflected in the cardiovascular system.
An impressive number of studies, designed in very different ways (from studies done on chimpanzees to different studies conducted on men, interventional or observational), consistently proved the direct connection between salt consumption and high blood pressure, a condition that leads to more serious ones: heart failure, coronary heart disease, stroke, kidney failure and others.
In 1989, an interesting study was conducted in two rural communities in Portugal, each with 800 inhabitants. In both, the salt consumption was high and around 30% of the inhabitants were suffering from high blood pressure. In one of the villages an educational program was launched, in which people were taught to lower their salt intake, and the inhabitants from the other village served as a comparison group. After a year, in the intervention group the average blood pressure was reduced by 3,5/5,0 mmHg, and after two years it was reduced by 5,0/5,1 mmHg—very significant statistical differences when compared to the control village, where diastolic blood pressure remained stable, and the systolic one increased.
Many more animal studies have shown the existence of a clear dose-response relationship between salt intake and blood pressure. Some epidemiological studies, with human subjects, suggest the existence of the following relationship: the higher the salt intake, the more blood pressure increases.[11] At the same time, long term studies, in which lowering the salt intake was maintained for at least 4 weeks, have shown a decrease in blood pressure by 5/3 mmHg for people suffering from high blood pressure and by 2/1 mmHg for those with normal blood pressure. This equals a decrease of approximately 14% of deaths connected to strokes and about 9% of deaths caused by coronary heart disease in hypertensives, and 6% and 4% respectively in normotensive patients.[12]
Disclaimer for skeptics
Some studies evaluating the effects of sodium decrease over a very short term (a few days or 1-2 weeks) did not show benefits from the point of view of cardiovascular health and some specialists have interpreted this data to prove the inefficacy of decreasing sodium intake in the diet.[13],[14] Still, these interpretations remain in the minority and tend to selectively interpret results; which, in the end, is not surprising at all, seeing that there are still health professionals who believe that tobacco is not that harmful for health, despite an overwhelming amount of evidence to the contrary. As it has been ironically pointed out, these skeptical articles must be taken with a grain of salt. At the end of 2012, almost simultaneously with the appearance of an article signed by a group of Polish researchers which contested the need to reduce salt consumption, the American Heart Association published an article in which the evidence was critically analysed and the conclusion was: “Indeed, evidence supporting recommendation for a low sodium intake in the general population remains robust and convincing.”[15]
Besides the connection between excessive salt consumption and issues with the cardiovascular system, there is data that shows that salt intake is associated with obesity through the consumption of soft drinks, as well as with kidney stones and asthma.[16] Salt excess also increases calcium excretion, a phenomenon which may have negative effects on bone health with an increased risk of osteoporosis. For Asian populations, it was proved that a high salt intake is associated with a high risk of gastric cancer.[17]
Where does the salt we consume come from?
At this moment, it would be useful to provide a short analysis of the main sources of salt in our diet. In developed countries, most of the sodium a person consumes is not from salt added to food when eating, which only accounts for 15% of total intake. A further 10% comes from natural unprocessed foods (fruits, vegetables, meat etc.).[18] The rest of the daily intake, 75%, is from salt contained in processed foods. The problem with this is that in the production process of most foods there is a reversal of the natural ratio between sodium and potassium ions. Fruits, vegetables, cereal, even milk and meat, when fresh contain relatively small amounts of sodium and large quantities of potassium. As a result of processing and packaging foods most of the potassium is lost and sodium—which we have already identified as being the harmful factor in salt—is added.
Can we reduce salt in our diets without turning our meals into torture?
We like salt because it adds flavour to food. When we try to reduce the salt intake, food might seem tasteless. But one can educate taste, and by gradually reducing salt, your taste buds can get used to smaller amounts. Furthermore, by choosing foods wisely, we can still have tasty and healthy meals. Get into the habit of checking the nutritional information labels and avoid or only consume in small quantities those which are high in sodium or salt. We can replace part of the salt we add to our food with tasty spices (caraway, mint, lovage, parsley, oregano, onion, garlic, fenugreek, etc.). We can buy fruits instead of salty snacks. It’s beneficial to reduce (or even eliminate) processed foods (cold cuts, bacon, instant soups, pickles, olives, soya sauce, ketchup) and increase the proportion of unprocessed ones, fruits and vegetables, which are low in sodium and rich in potassium. In fact, plant-based foods also have other benefits which we will explore in a future article.
Robert Ancuceanu, PhD, is a professor in the Faculty of Pharmacy at the Carol Davila University of Medicine and Pharmacy in Bucharest, Romania.