Too much of this ingredient leads to autoimmune diseases, new research shows. Here's how to cut back.
Scientists are looking at how salt affects our cells, and they're finding more reasons to avoid htoo much of it.
For more than a century, doctors have warned that too much salt in your diet can lead to high blood pressure, heart disease and stroke - and many of the reasons for these effects are well known. But recently scientists have been looking deeper, into the cellular level, and they are finding additional reasons to minimize sodium intake; it is bad for immune cells, creating patterns of gene expression and activity seen in a variety of autoimmune diseases such as multiple sclerosis, lupus, rheumatoid arthritis, and type-1 diabetes.
Salt is a major part of the ocean from which life evolved on this planet. We carry that legacy in our blood, which tastes salty. It is an important element for conducting electrical signals along nerves and balancing water and metabolites transported throughout our bodies. We need to consume about 500 milligrams of salt each day to maintain these functions, more with exercise and heavy sweating as that is a major way the body loses salt. The problem is that most Americans eating a modern western diet consume about 3400 milligrams, 1.5 teaspoons per day.
Evidence has been accumulating over the last few years that elevated levels of sodium can be harmful to at least some types of immune cells. The first signal came in monocytes, which are immune cells that travel to various tissues in the body, where some of them turn into macrophages, a subset of white blood cells that can directly kill microorganisms and make chemical signals that bring other types of immune cells into play.
Two years ago, Dominik N. Müller from the Max-Delbrueck-Center in Berlin, Germany and Markus Kleinewietfeld, an immunologist at Hasselt University in Belgium, ran a study where they fed people pizza and then measured their immune cell function. “We saw that in any monocytes, metabolic function was down, even after a single salty meal,” Kleinewietfeld says. It seemed to be the cellular equivalent of the sluggish feeling we get after eating too much. The cells were able to recover but more research is needed to answer questions about what dose of sodium causes impairment, how long the damage lasts, and whether there is a cumulative effect of salt toxicity.
Kleinewietfeld and his colleagues have hypothesized that too much salt could be a significant factor in the increased number of autoimmune diseases and allergies over the last few generations.
The latest series of experiments focused on a type of T cell called T regulatory cells, or Tregs. Most T cells release inflammatory mediators to fight pathogens and, once that job is done, Tregs come along to calm down their hyperactive brethren. Failure to do so can result in continued inflammation and possibly autoimmune diseases.
In the lab, Kleinewietfeld and his large team of international collaborators saw that high levels of sodium had a huge effect on Tregs, upregulating 1250 genes and downregulating an additional 1380 genes so that they looked similar to patterns of gene expression seen in autoimmune diseases.
Digging deeper, they found that sodium affected mitochondria, the tiny organelles inside of cells that produce much of its energy. The sodium was interfering with how the mitochondria use oxygen, which resulted in increased levels of an unstable form of oxygen that can damage cell function. The researchers injected those damaged Tregs into mice and found that they impaired the animals' immune function, allowing the inflammation to continue rather than shutting it down.
That finding dovetailed nicely with a 2019 paper in Nature from Navdeep Chandel's lab at Northwestern University, which showed in mice that inhibiting the mitochondrial use of oxygen reduced the ability of Tregs to regulate other T cells. “Mitochondria were controlling directly the immunosuppressive program, they were this master regulator tuning the right amount of genes to give you proper immunosuppression,” Chandel said. “And if you lose that function, then you get autoimmunity.”
Kleinewietfeld's team studied the Treg cells of humans and found that sodium can similarly decrease mitochondrial use of oxygen and immunosuppressive activity. “I would have never predicted that myself,” Chandel says, but now researchers can look at the mitochondria of patients with autoimmune disease and see if their gene expression also changes under high salt conditions. He sees the link between the patterns of gene expression in Tregs generated by high salt exposure and those patterns seen in autoimmune diseases, but he is cautious about claiming a causal effect.
Kleinewietfeld and his colleagues have hypothesized that too much salt could be a significant factor in the increased number of autoimmune diseases and allergies over the last few generations. He says a high salt diet could also have an indirect effect on immune function through the way it affects the gut microbiome and the molecules made by microbes when they break down food. But the research results are too preliminary to say that for sure, much less parse out the role of salt compared with other possible factors. “It is still an exciting journey to try to understand this field,” he says.
Additionally, it is difficult to say precisely how this research in animals and human cell cultures will translate into a whole human body. Individual differences in genetics can affect how the body absorbs, transports, and gets rid of sodium, such that some people are more sensitive to salt than are others.
So how should people apply these research findings to daily life?
Salt is obvious when we sprinkle it on at the table or eat tasty things like potato chips, but we may be unaware of sodium hidden in packaged foods. That's because salt is an easy and cheap way to boost the flavor of foods. And if we do read the labeled salt content on a package, we focus on the number for a single serving, but then eat more than that.
Last September, the U.S. Food and Drug Administration (FDA) began a process to update labels on the content of food, including what is meant by the word “healthy” and how food manufacturers can use the term. Many in the food industry are resisting those proposed changes.
Chandel cautions against trying to counter the effects of salt by reaching for foods or supplements full of antioxidants, which, in theory, could reduce the harmful effects on mitochondria caused by a heavy hand with the salt shaker.
Until labels are updated, it would be prudent to try to reduce sodium intake by cutting down on packaged foods while making your own food at home, where you know just how much salt has been added. The Mayo Clinic offers guidance on how to become more aware of the sodium in your diet and eat less of it.
Chandel thinks many people will struggle with minimizing salt in their diets. It’s similar to the challenge of eating less sugar, in that the body craves both, and it is difficult to fight that. He cautions against trying to counter the effects of salt by reaching for foods or supplements full of antioxidants, which, in theory, could reduce the harmful effects on mitochondria caused by a heavy hand with the salt shaker. “Dietary antioxidants have failed in just about every clinical trial, yet the public continues to take them,” Chandel says. But he is optimistic that research will lead us to a better understanding of how Tregs function, and uncover new targets for treating autoimmune diseases.
Growing Human Organs Inside Pigs Could Save Lives, But the U.S. Won't Fund the Research
Pigs in a barn.
The shortage of organs is a public health menace. Approximately 120,000 people in the U.S. need a lifesaving organ transplant. Of those, approximately 75,000 patients are on the active waiting list. Every day, nearly 20 individuals die from the shortage of organs in the United States.
Ethical concerns about human-animal chimera research might be dramatically overblown.
Scientists worldwide are developing new methods with potential to save countless patients in need of organs. Such approaches have tremendous potential, if only ethical and regulatory challenges could be overcome first.
One way that scientists are proposing to increase the number of transplantable organs is to produce organs from patient stem cells. Owed to their ability to grow limitlessly in the lab and form all tissue types, pluripotent stem cells from patients, in principle, could supply an infinite amount of cells that could potentially be transplanted back into patients. Unfortunately, all efforts to generate organs that can be transplanted into patients from stem cells to date have been unsuccessful.
A different encouraging approach is to generate patient organs inside livestock species, such as pigs. In the latest methods, interspecies chimeras – animals containing cells from both humans and animals – are generated by introducing human stem cells into early-stage animal embryos. Key genes essential for organ formation are disabled, allowing the introduced human stem cells to fill the empty space. In theory, this strategy will produce a human organ inside pigs or sheep.
Creating chimeras is not new in biology. Chimeras, or animals comprised of tissues from two different individuals, have already been deployed in research. Mouse chimeras are routinely used to create genetically engineered mice to study genes. The concept of generating human organs inside pigs or sheep comes from previous studies involving interspecies chimeras generated between mice and rats. Past experiments have demonstrated that it is possible to generate a rat pancreas inside a mouse.
Scientific and Ethical Obstacles
Unfortunately, chimera research has faced hurdles that have impeded progress. Of note, attempts to generate interspecies chimeras by several groups have failed. The results of these studies indicate that human cells appear unable to grow inside mouse embryos. The levels of human chimerism – the number of human cells inside the host animal embryo – appear too low to support any human organ generation.
Another obstacle is that chimera generation is ethically controversial. Some question the moral status of an animal that is comprised of human and animal cells. The most concerning question is whether human cells will contribute to the host animal's brain, potentially altering the cognition of the animal. These issues have prompted scientists to proceed very cautiously with chimera experiments. However, such concerns might be dramatically overblown. This is because the levels of human chimerism are too low to cause any significant change in animal brain function.
The ethical controversy has affected research policy in the United States. In the United States, the National Institutes of Health (NIH), the major funding body of biomedical research, blocked funding for chimera research while ethical questions were considered. Later, it was proposed that a new review process would be instated for chimera research. However, no change in policy has actually happened. The restrictive NIH policy is a major barrier to chimera research progress because laboratories around the United States cannot obtain funding for it. Lifting the restrictions on NIH funding for chimera research would dramatically accelerate chimera research.
Nonetheless, despite the past and current hurdles that chimera research has faced, new advances are changing the landscape of chimera research.
It is time to lift restrictions on chimera research so that its promise can be fully realized.
Progress on the Horizon
Scientists are developing improved strategies to increase the numbers of cells in animal embryos to the point where it might be possible to generate a human organ in an animal. For example, it has been suggested that the human stem cells researchers have been using cannot grow in animals. Scientists have made advances in generating new types of human stem cells that might have an improved ability to form chimeras.
Additionally, scientists have identified some barriers responsible for the failure to generate chimeras. For example, preventing cell death and enhancing the ability of stem cells to compete with host animal tissues also improves the numbers of human cells to the point where human organs can be generated inside an animal.
Finally, a relaxation of regulatory hurdles in other countries has created a more permissive environment for human-animal interspecies chimera research. In March, the Japanese government approved the first such experiments that could comprise a new way of generating organs from patients for transplantation.
Additionally, in spite of the somewhat negative attention that chimera generation has received, the International Society for Stem Cell Research (ISSCR) supports the new Japanese policies allowing chimera experiments. The ISSCR maintains that research involving the generation of chimeras should be permitted, as long as rigorous oversight and ethics review occur.
Chimera research has the potential to transform medicine. Of all the impediments, the NIH restrictions on funding remain the single most significant barrier. It is time to lift restrictions on chimera research so that its promise can be fully realized. One day, it might be possible to grow patient-specific organs inside of livestock animals such as pigs and sheep, saving thousands of human lives. But to change our current policy, the public, scientists, and bioethicists must first agree that this critical cause is worth fighting for.
In China, Prisoners of Conscience Are Being Murdered for Their Organs to Fuel Transplant Tourism
A somber photo of the Great Wall of China.
Organ transplantation can dramatically improve or save lives. A heart transplant can literally give a person a new lease of life, while a kidney transplant frees the recipient from lengthy spells on dialysis.
A people's tribunal in London has recently found that in China, organs are sourced from prisoners of conscience who are killed on demand to fuel the lucrative organ transplantation market.
To protect the integrity of organ transplantation, there are strict ethical guidelines. When organs are sourced from deceased persons, the donation must be voluntary, donors must die naturally before any organs are taken, and death must not be hastened to provide organs. These ethical guidelines protect donors and provide assurance to transplant recipients that their organs have been sourced ethically.
However, not all countries follow these ethical guidelines. A people's tribunal in London has recently found that in China, organs are sourced from prisoners of conscience who are killed on demand to fuel the lucrative organ transplantation market. This conclusion, reported at the United Nations Human Rights Council on September 24, was not reached lightly.
The independent China Tribunal, made up of four human rights lawyers, one surgeon with transplant experience, an academic who specialises in China studies and a businessman with human rights interests, spent over a year looking at written materials and heard evidence from over 50 witnesses in five days of hearings. Their grim conclusion, that prisoners of conscience are murdered for their organs, confirms the findings of earlier investigations.
Questions first arose over China's transplant system when the numbers of transplants rose dramatically after 2000. Transplant capacity rapidly increased; new infrastructure was built and staff were trained. Hospital websites offered livers, hearts and kidneys available in a matter of days or weeks, for a price. Foreigners were encouraged to come to China to avoid lengthy transplant waiting lists in their home countries.
At the time, it was a mystery as to how China had a ready supply of organs, despite having no volunteer donation system. Eventually, in 2006, the Chinese government stated that organs were removed from prisoners who had been found guilty and sentenced to the death penalty. But this explanation did not ring true. Death row prisoners often have poor health, including high rates of infectious diseases, making them poor candidates for donation. By contrast, the organs offered for sale were promised to be healthy.
In 2006, the first clues about the source of the organs emerged. A woman called Annie reported that her surgeon husband had been present during organ removal from Falun Gong practitioners who were still breathing as the scalpels cut into them. A subsequent investigation by two Canadian human rights lawyers examined multiple sources of evidence, concluding that murdered Falun Gong practitioners were indeed the source of the organs.
The evidence included testimony from practitioners who had been imprisoned, tortured, and later released. During imprisonment, many practitioners reported blood and other medical tests examining the health of their organs—tests that were not performed on any other prisoners. Phone calls made to Chinese hospitals by investigators posing as patients were offered rapid access to fresh organs from Falun Gong practitioners. The organs were guaranteed to be healthy, as the practice forbids smoking tobacco and drinking alcohol.
Since 2006, evidence has continued to accumulate. China has a huge transplant industry and no plausible source of voluntary organ donations. Unlike the rest of the world, Chinese waiting times remain very short. Foreigners continue to come to China to avoid lengthy waiting lists. Prisoners of conscience, including Tibetans and Uyghurs as well as Falun Gong practitioners, are still being imprisoned and medically tested.
The Chinese government continues to deny these crimes, claiming that there is a volunteer donor system in place.
The China Tribunal heard from Uyghur witnesses who had recently been inside the notorious labour camps (also called "re-education" centers) in Xin Xiang. The witnesses reported terrible conditions, including overcrowding and torture, and were forced to have medical examinations. They saw other prisoners disappear without explanation following similar medical tests. As recently as 2018, doctors in Chinese hospitals were promising potential patients healthy Falun Gong organs in taped phone calls.
The Chinese government continues to deny these crimes, claiming that there is a volunteer donor system in place. In the Chinese system, prisoners are counted as volunteers.
China's forced organ harvesting from prisoners of conscience has international implications. A recent study found that most published Chinese transplant research is based on organs sourced from prisoners. International ethical guidance prohibits taking organs from prisoners and prohibits publication of research based on transplanted material from prisoners. The authors of that study called for retractions of the papers, some of which are in well-known scientific journals. So far Transplantation and PLOS One are among the journals that have already retracted over twenty articles in response. On questioning from the editors, the authors of the papers failed to respond or could not verify that the organs in the transplant research came from volunteers.
The international community has a moral obligation to act together to stop forced organ harvesting in China.
The China Tribunal concluded that forced organ harvesting remains China's main source of transplant organs. In their view, the commission of Crimes Against Humanity against the Uyghurs and Falun Gong has been proved beyond reasonable doubt. By their actions, the Chinese government has turned a life-saving altruistic practice into our worst nightmare. The international community has a moral obligation to act together to stop forced organ harvesting in China, and end these crimes against humanity.