Too much salt weakens the immune system
A diet rich in salt weakens the antibacterial immune defense
Date:
March 25, 2020
Source:
University of Bonn
Summary:
A high-salt diet is not only bad for one's blood pressure, but also for the immune system. Mice fed a high-salt diet were found to suffer from much more severe bacterial infections. Human volunteers who consumed additional six grams of salt per day also showed pronounced immune deficiencies. This amount corresponds to the salt content of two fast food meals.
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A high-salt diet is not only bad for one's blood pressure, but also for the immune system. This is the conclusion of a current study under the leadership of the University Hospital Bonn. Mice fed a high-salt diet were found to suffer from much more severe bacterial infections. Human volunteers who consumed an additional six grams of salt per day also showed pronounced immune deficiencies. This amount corresponds to the salt content of two fast food meals. The results are published in the journal Science Translational Medicine.
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Five grams a day, no more: This is the maximum amount of salt that adults should consume according to the recommendations of the World Health Organization (WHO). It corresponds approximately to one level teaspoon. In reality, however, many Germans exceed this limit considerably: Figures from the Robert Koch Institute suggest that on average men consume ten, women more than eight grams a day.
This means that we reach for the salt shaker much more than is good for us. After all, sodium chloride, which is its chemical name, raises blood pressure and thereby increases the risk of heart attack or stroke. But not only that: "We have now been able to prove for the first time that excessive salt intake also significantly weakens an important arm of the immune system," explains Prof. Dr. Christian Kurts from the Institute of Experimental Immunology at the University of Bonn.
This finding is unexpected, as some studies point in the opposite direction. For example, infections with certain skin parasites in laboratory animals heal significantly faster if these consume a high-salt diet: The macrophages, which are immune cells that attack, eat and digest parasites, are particularly active in the presence of salt. Several physicians concluded from this observation that sodium chloride has a generally immune-enhancing effect.
The skin serves as a salt reservoir
"Our results show that this generalization is not accurate," emphasizes Katarzyna Jobin, lead author of the study, who has since transferred to the University of Würzburg. There are two reasons for this: Firstly, the body keeps the salt concentration in the blood and in the various organs largely constant. Otherwise important biological processes would be impaired. The only major exception is the skin: It functions as a salt reservoir of the body. This is why the additional intake of sodium chloride works so well for some skin diseases.
However, other parts of the body are not exposed to the additional salt consumed with food. Instead, it is filtered out by the kidneys and excreted in the urine. And this is where the second mechanism comes into play: The kidneys have a sodium chloride sensor that activates the salt excretion function. As an undesirable side effect, however, this sensor also causes so-called glucocorticoids to accumulate in the body. And these in turn inhibit the function of granulocytes, the most common type of immune cell in the blood.
Granulocytes, like macrophages, are scavenger cells. However, they do not attack parasites, but mainly bacteria. If they do not do this to a sufficient degree, infections proceed much more severely. "We were able to show this in mice with a listeria infection," explains Dr. Jobin. "We had previously put some of them on a high-salt diet. In the spleen and liver of these animals we counted 100 to 1,000 times the number of disease-causing pathogens." Listeria are bacteria that are found for instance in contaminated food and can cause fever, vomiting and sepsis. Urinary tract infections also healed much more slowly in laboratory mice fed a high-salt diet.
Sodium chloride also appears to have a negative effect on the human immune system. "We examined volunteers who consumed six grams of salt in addition to their daily intake," says Prof. Kurts. "This is roughly the amount contained in two fast food meals, i.e. two burgers and two portions of French fries." After one week, the scientists took blood from their subjects and examined the granulocytes. The immune cells coped much worse with bacteria after the test subjects had started to eat a high-salt diet.
In human volunteers, the excessive salt intake also resulted in increased glucocorticoid levels. That this inhibits the immune system is not surprising: The best-known glucocorticoid cortisone is traditionally used to suppress inflammation. "Only through investigations in an entire organism were we able to uncover the complex control circuits that lead from salt intake to this immunodeficiency," stresses Kurts. "Our work therefore also illustrates the limitations of experiments purely with cell cultures."
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Materials provided by University of Bonn. Note: Content may be edited for style and length.
⬇️⬇️⬇️⬇️Ahh e os sulfitos ( enfio aqui este) :⬇️⬇️⬇️⬇️
Abstract
Sulfites and other preservatives are considered food additives to limit bacterial contamination, and are generally regarded as safe for consumption by governmental regulatory agencies at concentrations up to 5000 parts per million (ppm). Consumption of bactericidal and bacteriostatic drugs have been shown to damage beneficial bacteria in the human gut and this damage has been associated with several diseases. In the present study, bactericidal and bacteriostatic effects of two common food preservatives, sodium bisulfite and sodium sulfite, were tested on four known beneficial bacterial species common as probiotics and members of the human gut microbiota. Lactobacillus species casei, plantarum and rhamnosus, and Streptococcus thermophilus were grown under optimal environmental conditions to achieve early log phase at start of experiments. Bacterial cultures were challenged with sulfite concentrations ranging between 10 and 3780 ppm for six hours. To establish a control, a culture of each species was inoculated into media containing no sulfite preservative. By two hours of exposure, a substantial decrease (or no increase) of cell numbers (based on OD600 readings) were observed for all bacteria types, in concentrations of sulfites between 250–500 ppm, compared to cells in sulfite free media. Further testing using serial dilution and drop plates identified bactericidal effects in concentrations ranging between 1000–3780 ppm on all the Lactobacillus species by 4 hours of exposure and bactericidal effects on S. thermophilus in 2000ppm NaHSO3 after 6 hours of exposure.
Introduction
The term “sulfites” in its applications for food and drugs refers to sulfur dioxide gas; hydrogen sulfites; metabisulfites; and sulfur salts containing potassium, calcium, or sodium. These molecules are additives to beer, wine, juices, dried fruit, processed fish, seafood, meats, and some canned goods. They also occur naturally in some fermented foods as metabolites of yeast [1]. Sulfite additives are intended primarily for controlling microbial growth, preventing browning and food spoilage. Limited studies have been done to examine the effects of sulfites on lactic acid producing bacteria (LAB) prevalent during wine production which have illustrated their significant and selective inhibitory properties [2]. Under the 1958 Food Additives Amendment to the Federal Food, Drug, and Cosmetic Act, several food preservatives including sulfites were declared “Generally Regarded as Safe” (GRAS). Since that time, sulfites have been subject to multiple reviews and shown by some studies to be dangerous to humans when ingested at levels as low as 1 ppm [1,3–7]. Regulations for their use as food preservatives have changed as it has become increasingly clear that the levels of sulfites in many foods pose health concerns for some individuals. Due to insufficient statistical data regarding individual sensitivities and consumer intake levels [8,9], it has been difficult to identify the exact level at which these preservatives become harmful. Reactions can occur between these additives and primary constituents naturally present in food, as well as during preparation and digestion, contributing to this conundrum.
Currently, Health Canada lists a maximum concentration of sulfites allowable in some foods to be at 5000 ppm [10]. An acceptable daily intake (ADI) for sulfites was established by the Joint FAO/WHO Expert Committee on Food Additives (JECFA) in 1974 (0.7mg/kg body weight, expressed as sulfur dioxide, i.e. equivalent to 42 mg for a60 kg adult) and was also adopted by the Scientific Committee for Food (SCF) in 1994. The FDA requires that foods containing sulfites at concentrations greater than 10 ppm are labeled accordingly [11]. Internationally, several boards have been organized to evaluate the subject further. The Codex Committee on Food Additives (CCFA) is one such organization that has established a General Standard of Food Additives to serve as a guideline for maximum limits [8,9]. The CCFA analyzes collected data from many countries, including Germany, Australia, Brazil, Italy, France and the US. Different countries have adopted unique regulation of maximum limits of sulfites; some with national regulations much higher than suggested by the Committee. Others, despite keeping within guidelines, reported that the average consumer daily intake was much higher than their national ADI [8,11].
Analysis of sulfite concentration in red and white wine yielded a mean concentration of 70 mg/L and 122 mg/L respectively. This means that drinking about two glasses of wine (450 mL) a day equates to an intake of 75 to 130% of ADI for a 60-kg person. This statistic, combined with additional intake of sulfites common in western diet may bring the average total dietary exposure to sulfites to a total of 294% of ADI for adults and 325% for children [1,8]. It is therefore not unreasonable to consider that the average consumer is often subject to levels well over the amount generally regarded as safe. With this in mind, it is important to analyze what the impacts of excessive exposure to sulfites may have on the resident and transient microbiota of the mouth and digestive system, where they are introduced most prevalently.
The gastrointestinal tract of humans is colonized by about 800 different species of bacteria [12]. The mouth microbiome has been shown to have approximately six different phyla of bacteria with approximately 25% of the total population being Streptococcus species and another 12.5% made up of Lactobacillus species [13]. The relationship between these communities and their hosts has historically been considered commensal, though recent and ongoing studies continue to reveal benefits linked to the presence of these microflora. Research has shown these bacteria to be involved in many metabolic processes resulting in biosynthesis of molecules which act on the gut and throughout the body [12,14]. Some bacterial species produce neurotransmitters which act on the brain and affect mood. S. thermophilus generates serotonin while some Lactobacillus produce acetylcholine and gamma aminobutyric acid (GABA) [15]. Lactobacillus and Streptococcus species are also known to produce several B vitamins including B1 (thiamine), B2 (riboflavin), B9 (folic acid) and B12 (cobalamin). Lactobacillus plantarum is known to synthesize B2 in abundance. Lactobacillus casei is known to bind and carry thiamine, which S. thermophilus has been found to produce small amounts of, as well as pyridoxine (B6). S. thermophilus and L. plantarum synthesize folate (B9), a molecule used in cell division and construction of DNA and other genetic material [16,17]. One study suggests that lactate produced metabolically by S. thermophilus inversely impacts infection of Clostridium difficile in the intestinal tract of mice [18]. Noted to encourage homeostasis of the intestines, the gut microbiota also has a strong influence on development of intestinal microvilli and contributes to the strength and resilience of the overall host immune defense [12]. A connection the health of the gut microbiome and the health of the mouth microbiome has been indicated in several studies related to human diseases of the digestive and immune systems [13]. However, to date there have been no studies done to look directly at the potential effects of food preservatives on the beneficial bacteria that make up the human gut or mouth microbiome.
All four bacterial types assayed here, are commonly found in probiotic supplements as well as fermented foods. They may also be found as part of the normal gut microbiome or more often as transients that interact with the normal flora and our immune system. The Lactobacillus species tested were recently determined to be among the four most “robust” in their ability to survive gastric passage and to be found “metabolically active” in the ileum and colon. Additionally, ingestion of lactic acid bacteria (LAB) has been shown to positively impact the commensal gut residents by altering metabolic outputs of carbohydrate consumption while negatively affecting potential pathogens by decreasing the pH, production of biofilms that encourage the growth of commensals and the production of antimicrobials like bacteriocins and hydrogen peroxide [19].
When presented with this information, it seems pertinent to ascertain the impact that exposure to food preservatives including sulfites may have on the gut and mouth microbiota. Experiments were designed to establish a basic understanding of the effects of two types of sulfite preservatives (at concentrations deemed GRAS by the FDA) on the growth of four beneficial gut microbes.
