If there is one Christmas tradition that many households share, it is the time spent around a table full of food. But doctors say there is one condiment we should watch out for: salt. Excessive consumption can increase the risk of cardiovascular issues, including hypertension and renal problems, among other conditions. A recent study in mice suggests that a high-salt diet is also associated with high levels of stress hormones. The World Health Organization recommends no more than five grams per day for adults, but most of the population consumes twice that amount.
Salt – sodium chloride – is essential to life and to every diet. Humans need sodium in order to perform vital functions, such as the transmission of nerve signals. “All civilizations have lived in areas where they could get salt. It is essential. If we were to reduce our consumption to zero, we wouldn’t survive,” explains Jordi Salas-Salvador, a Spanish professor in nutrition.
Salt is not inherently harmful. The problem lies in eating more than necessary: “We consume more salt than we put on our food with the salt shaker. It is already in the food, and it is used as a preservative or to enhance the flavor. For example, the ham we eat on Christmas has enormous quantities of salt. It is hidden in the food. Cookies, for example, aside from sugar, also have salt,” the expert explains.
The World Health Organization recommends for adults to not exceed two grams daily of sodium, or five grams of salt, but most people ingest between nine and 12 grams of salt each day. “It is estimated that each year 2.5 million deaths could be avoided if the global salt consumption were reduced to the recommended level,” says the WHO, which hopes to reduce global salt consumption by 30% by 2025.
Excess salt can damage health in several ways. The most studied is its association with arterial hypertension and related cardiovascular problems, such as heart attacks, strokes and vascular dementia, Salsa-Salvador notes. It can also cause kidney problems. A recent study also found that it can increase the levels of stress hormones.
The study was conducted on mice and published in the magazine Cardiovascular Research. It concluded that animals exposed to higher salt consumption had higher levels of glucocorticoids (cortisol in humans, corticosterone in rats), hormones with important cardiovascular, cognitive and metabolic functions, which the body releases as a response to stressful or threatening situations. Scientists from the University of Edinburgh demonstrated that exposure to excessive salt consumption activates the hypothalamic-pituitary-adrenal axis, a key system in humans’ stress response. Their response to environmental stressors was amplified. “This axis is well known: the hormones that are produced in the hypothalamus act on the pituitary, which stimulates, in turn, the adrenal glands, located in the kidneys, which produce glucocorticoids. The activation of this axis has also been related to metabolic diseases [such as diabetes or obesity], and it is said that it may be one of the causes,” says Salas-Salvador.
Francisco Pita, a member of the Nutrition area of the Spanish Society of Endocrinology and Nutrition, explains that “when there is a stressful situation for the body, that is, an attack in which the person needs to respond or defend themselves, cortisol is released.” The problem is when it is released excessively and continuously over time. “Excessive activation of the hypothalamic-pituitary-adrenal axis is bad because it ends up creating an excess of glucocorticoids, which can cause hypertension, fluid retention, weight gain, diabetes, hair growth and muscle weakness, poor wound healing or bruising. There are diseases caused by excessive activation of the axis, such as Cushing’s syndrome, a group of symptoms that are produced by an excess of glucocorticoid action,” the endocrinologist explains.
With all the caveats that a study on animals implies, the association found in this study aligns with previous research that reflected a relationship between salt intake and urinary cortisol excretion. “We can never fully translate studies in mice to humans. The sodium levels that stimulate stress will surely be different, but the authors have tried to simulate excess salt, and the mechanisms are probably very similar, although more study is needed. In humans, we know that excess salt produces more glucocorticoids and increases their excretion,” adds the Rovira i Virgili professor. Pita urges caution and points out that “it remains to be seen whether or not an eventual increase in the level of glucocorticoids associated with excessive salt consumption is relevant” for humans.
Salas-Salvador points out, regardless, that there are people who are especially sensitive to the effects of salt and show an exaggerated hypertensive response to high salt intake. According to the study published in Cardiovascular Research, salt sensitivity is also found in approximately 30% of healthy humans “and independently increases cardiovascular risk and mortality risk.”
José Manuel Vázquez Rodríguez, head of the Cardiology Service of the A Coruña Hospital and head of the Cardiovascular Diseases Area of the A Coruña Biomedical Research Institute, admits that how, exactly, excessive salt consumption leads to hypertension is unknown. He outlines some processes, though: “We know that the more salt consumed, the more sodium in the body, and that implies more fluid retention that remains in the intravascular space. [People who are more sensitive to salt] are also more sensitive to vasopressor substances in the arteries that cause them to constrict and increase pressure.” The cardiologist also points out that high blood pressure “produces arterial disease and is a risk factor for disease in these vessels and increases the risk of heart attack or stroke.” “It also causes kidney disease because the renal arteries are damaged and can cause kidney failure. In nephroangiosclerosis, for example, the renal arterioles are damaged, they become more rigid and the arterial wall becomes diseased. This causes the kidney to not filter well, and waste products are not removed well,” he adds.
Other research has also linked excess salt intake to an increased risk of developing autoimmune diseases, although scientific evidence in this field is more limited. Regarding cancer, an association has also been found between the consumption of foods high in salt and an increased risk of developing gastric tumors.
Salas-Salvador points out that excess salt’s impact on health is correlated with time: “It is the continued consumption that causes disaster.” To keep salt intake at healthy levels, the WHO recommends not adding it during food preparation, removing the salt shaker from the table, limiting the consumption of salty snacks and choosing low-sodium products. The health agency also dismantles some myths, including that salt-free foods have no taste: human beings can adapt to eating with less salt because the taste buds get used to it.
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