鹽分過多會削弱免疫系統 Too much salt weakens the immune system

News Release 25-Mar-2020

Study by the University Hospital of Bonn shows: A diet rich in salt weakens the antibacterial immune defense

University of Bonn

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.

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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The University of Bonn is one of Germany’s leading universities in the field of immunology. It is home to the Cluster of Excellence ImmunoSensation, of which Prof. Kurts is a member of the Executive Board. It is the only Cluster of Excellence in Germany in this field. Researchers from university hospitals in Regensburg, Hamburg, Erlangen and Melbourne (Australia) also participated in the study.

Publication: Katarzyna Jobin, Natascha E. Stumpf, Sebastian Schwab, Melanie Eichler, Patrick Neubert, Manfred Rauh, Marek Adamowski, Olena Babyak, Daniel Hinze, Sugirthan Sivalingam, Christina K. Weisheit, Katharina Hochheiser, Susanne Schmidt, Mirjam Meissner, Natalio Garbi, Zeinab Abdullah, Ulrich Wenzel, Michael Hölzel, Jonathan Jantsch and Christian Kurts: A high-salt diet compromises antibacterial neutrophil responses through hormonal perturbation; Science Translational Medicine; DOI: 10.1126/scitranslmed.aay3850

Contact:

Prof. Dr. Christian Kurts
Institut für Experimentelle Immunologie
Universitätsklinikum Bonn
Tel. +49-(0)228-28711050
E-mail: [email protected]

新聞稿2020年3月25日
鹽分過多會削弱免疫系統

波恩大學醫院的一項研究表明：富含鹽的飲食會削弱抗菌免疫防禦能力

波恩大學
圖片

圖像：（左起）Katarzyna Jobin博士，Natascha Ellen Stumpf，Melanie Eichler，Christian Kurts教授，Olena Babyak和Mirjam Meissner。查看更多

圖片來源：（c）照片：Max Germer

高鹽飲食不僅對人的血壓有害，而且對免疫系統也有害。這是波恩大學醫院領導下的一項最新研究的結論。發現餵食高鹽飲食的小鼠患有更嚴重的細菌感染。每天額外攝入六克鹽的人類誌願者也表現出明顯的免疫缺陷。這個量對應於兩頓快餐的鹽含量。研究結果發表在《科學轉化醫學》雜誌上。

每天五克，不再增加：這是根據世界衛生組織（WHO）的建議，成年人應攝入的最大鹽量。它大約相當於一個水平的茶匙。然而實際上，許多德國人大大超過了這個限制：羅伯特·科赫研究所的數據顯示，男人平均每天要消耗10克，女人每天要消耗8克以上。

這意味著我們對鹽罐的追求遠不止對我們有好處。畢竟，氯化鈉是其化學名稱，它會導致血壓升高，從而增加心髒病發作或中風的風險。不僅如此：“我們現在已經能夠首次證明過量攝入鹽分也能顯著削弱免疫系統的重要組成部分，”美國大學實驗免疫研究所的克里斯蒂安·庫爾茨（Christian Kurts）博士解釋說。波恩

這一發現是出乎意料的，因為一些研究指向相反的方向。例如，食用高鹽飲食的實驗動物中某些皮膚寄生蟲的感染會明顯更快地康復：巨噬細胞是攻擊，食用和消化寄生蟲的免疫細胞，在有鹽的情況下特別活躍。幾位醫生從這一發現得出結論，氯化鈉具有一般的免疫增強作用。

皮膚充當鹽庫

該研究的主要作者Katarzyna Jobin強調說：“我們的結果表明這種概括是不准確的。”他後來轉任維爾茨堡大學。造成這種情況的原因有兩個：首先，人體使血液和各個器官中的鹽分濃度保持基本恆定。否則，重要的生物學過程將受到損害。唯一的主要例外是皮膚：它起著人體鹽分的作用。這就是為什麼額外攝入氯化鈉對某些皮膚疾病如此有效的原因。

但是，身體的其他部分沒有暴露於食物所消耗的額外鹽分中。取而代之的是，它被腎臟過濾掉並排泄到尿液中。這就是第二種機制起作用的地方：腎臟具有激活鈉鹽排泄功能的氯化鈉傳感器。然而，作為不希望有的副作用，該傳感器還引起所謂的糖皮質激素在體內積聚。這些反過來又抑制了粒細胞的功能，粒細胞是血液中最常見的免疫細胞類型。

粒細胞像巨噬細胞一樣，是清除細胞。但是，它們不攻擊寄生蟲，而主要攻擊細菌。如果他們沒有做到足夠的程度，感染將更加嚴重地進行。喬賓博士解釋說：“我們能夠在患有李斯特菌感染的小鼠中證明這一點。” “我們以前將它們中的一些放在高鹽飲食中。在這些動物的脾臟和肝臟中，我們計算出致病性病原體數量的100到1000倍。”李斯特菌是細菌，例如在受污染的食物中發現，會引起發燒，嘔吐和敗血症。餵高鹽飲食的實驗小鼠泌尿道感染的癒合也要慢得多。

氯化鈉似乎也對人體免疫系統有負面影響。庫爾茨教授說：“我們檢查了志願者，他們除了每天攝入六克鹽以外還攝入了六克鹽。” “這大約是兩頓快餐中所含的數量，即兩個漢堡和兩份炸薯條。”一周後，科學家從他們的受試者那裡抽血並檢查了粒細胞。在測試對像開始進食高鹽飲食後，免疫細胞對細菌的抵抗力要差得多。

在人類誌願者中，過多的鹽攝入也會導致糖皮質激素水平升高。 抑制免疫系統就不足為奇了：最著名的糖皮質激素可的松傳統上用於抑制炎症。 “只有通過對整個有機體的調查，我們才能發現導致鹽攝入量增加導致這種免疫缺陷的複雜控制迴路，” Kurts強調說。 “因此，我們的工作也說明了純細胞培養實驗的局限性。”