Too much of this ingredient leads to autoimmune diseases, new research shows. Here's how to cut back.
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.
Debates over transgender athletes rage on, with new state bans and rules for Olympians, NCAA sports
Ashley O’Connor, who was biologically male at birth but identifies as female, decided to compete in badminton as a girl during her senior year of high school in Downers Grove, Illinois. There was no team for boys, and a female friend and badminton player “practically bullied me into joining” the girls’ team. O’Connor, who is 18 and taking hormone replacement therapy for her gender transition, recalled that “it was easily one of the best decisions I have ever made.”
She believes there are many reasons why it’s important for transgender people to have the option of playing sports on the team of their choice. “It provides a sense of community,” said O’Connor, now a first-year student concentrating in psychology at the College of DuPage in Glen Ellyn, Illinois.
“It’s a great way to get a workout, which is good for physical and mental health,” she added. She also enjoyed the opportunity to be competitive, learn about her strengths and weaknesses, and just be normal. “Trans people have friends and trans people want to play sports with their friends, especially in adolescence,” she said.
However, in 18 states, many of which are politically conservative, laws prohibit transgender students from participating in sports consistent with their gender identity, according to the Movement Advancement Project, an independent, nonprofit think tank based in Boulder, Colo., that focuses on the rights of LGBTQ people. The first ban was passed in Idaho in 2020, although federal district judges have halted this legislation and a similar law in West Virginia from taking effect.
Proponents of the bans caution that transgender females would have an unfair biological advantage in competitive school sports with other girls or women as a result of being born as stronger males, potentially usurping the athletic accomplishments of other athletes.
“The future of women’s sports is at risk, and the equal rights of female athletes is being infringed,” said Penny Nance, CEO and president of Concerned Women for America, a legislative action committee in D.C. that seeks to impact culture to promote religious values.
“As the tidal wave of gender activism consumes sports from the Olympics on down, a backlash is being felt as parents are furious about the disregard for their daughters who have worked very hard to achieve success as athletes,” Nance added. “Former athletes, whose records are being shattered, are demanding answers.”
Meanwhile, opponents of the bans contend that they bar transgender athletes from playing sports with friends and learning the value of teamwork and other life lessons. These laws target transgender girls most often in kindergarten through high school but sometimes in college as well. Many local schools and state athletic associations already have their own guidelines “to both protect transgender people and ensure a level playing field for all athletes,” according to the Movement Advancement Project’s website. But statewide bans take precedence over these policies.
"It’s easy to sympathize on some level with arguments on both sides, and it’s likely going to be impossible to make everyone happy,” said Liz Joy, a past president of the American College of Sports Medicine.
In January, the National Collegiate Athletic Association (NCAA), based in Indianapolis, tried to sort out the controversy by implementing a new policy. It requires transgender students participating in female sports to prove that they’ve been taking treatments to suppress testosterone for at least one year before competition, as well as demonstrating that their testosterone level is sufficiently low, depending on the sport, through a blood test.
Then, in August, the NCAA clarified that these athletes also must take another blood test six months after their season has started that shows their testosterone levels aren’t too high. Additional guidelines will take effect next August.
Even with these requirements, “there is no plan that is going to be considered equitable and fair to all,” said Bradley Anawalt, an endocrinologist at the University of Washington School of Medicine. Biologically, he noted, there is still some evidence that a transgender female who initiates hormone therapy with estrogen and drops her testosterone to very low levels may have some advantage over other females, based on characteristics such as hand and foot size, height and perhaps strength.
Liz Joy, a past president of the American College of Sports Medicine, agrees that allowing transgender athletes to compete on teams of their self-identifying gender poses challenges. “It’s easy to sympathize on some level with arguments on both sides, and it’s likely going to be impossible to make everyone happy,” said Joy, a physician and senior medical director of wellness and nutrition at Intermountain Healthcare in Salt Lake City, Utah. While advocating for inclusion, she added that “sport was incredibly important in my life. I just want everyone to be able to benefit from it.”
One solution may be to allow transgender youth to play sports in a way that aligns with their gender identity until a certain age and before an elite level. “There are minimal or no potential financial stakes for most youth sports before age 13 or 14, and you do not have a lot of separation in athlete performance between most boys and girls until about age 13,” said Anwalt, who was a reviewer of the Endocrine Society’s national guidelines on transgender care.
Myron Genel, a professor emeritus and former chief of pediatric endocrinology at Yale School of Medicine, said it’s difficult to argue that height gives transgender females an edge because in some sports tall women already dominate over their shorter counterparts.
He added that the decision to allow transgender females to compete with other girls or women could hinge on when athletes began taking testosterone blockers. “If the process of conversion from male to female has been undertaken in the early stages of puberty, from my perspective, they have very little unique advantage,” said Genel, who advised the International Olympic Committee (IOC), based in Switzerland, on testosterone limits for transgender athletes.
Because young athletes’ bodies are still developing, “the differences in natural abilities are so massive that they would overwhelm any advantage a transgender athlete might have,” said Thomas H. Murray, president emeritus of The Hastings Center, a pioneering bioethics research institute in Garrison, New York, and author of the book “Good Sport,” which focuses on the ethics and values in the Olympics and other competitions.
“There’s no good reason to limit the participation of transgender athletes in the sports where male athletes don’t have an advantage over women,” such as sailing, archery and shooting events, Murray said. “The burden of proof rests on those who want to restrict participation by transgender athletes. They must show that in this sport, at this level of competition, transgender athletes have a conspicuous advantage.”
Last year, the IOC issued a new framework emphasizing that the Olympic rules related to transgender participation should be specific to each sport. “This is an evolving topic and there has been—as it will continue to be—new research coming out and new developments informing our approach,” and there’s currently no consensus on how testosterone affects performance across all sports, an IOC spokesperson told Leaps.org.
Many of the new laws prohibiting transgender people from competing in sports consistent with their gender identity specifically apply to transgender females. Yet, some experts say the issue also affects transgender males, nonbinary and intersex athletes.
“There has been quite a bit of attention paid to transgender females and their participation in biological female sports and almost minimal focus on transgender male competition in male sports or in any sports,” said Katherine Drabiak, associate professor of public health law and medical ethics at University of South Florida in Tampa. In fact, “transgender men, because they were born female, would be at a disadvantage of having less lean body mass, less strength and less muscular area as a general category compared to a biological male.”
While discussing transgender students’ participation in sports, it’s important to call attention to the toll that anti-transgender legislation can take on these young people’s well-being, said Jonah DeChants, a research scientist at The Trevor Project, a suicide prevention and mental health organization for LGBTQ youth. Recent polling found that 85 percent of transgender and nonbinary youth said that debates around anti-transgender laws had a negative impact on their mental health.
“The reality is simple: Most transgender girls want to play sports for the same reasons as any student—to benefit their health, to have fun, and to build connection with friends,” DeChants said. According to a new peer-reviewed qualitative study by researchers at The Trevor Project, many trans girls who participated in sports experienced harassment and stigma based on their gender identity, which can contribute to poor mental health outcomes and suicide risk.
In addition to badminton, O'Connor played other sports such as volleyball, and she plans to become an assistant coach or manager of her old high school's badminton team.
Ashley O'Connor
However, DeChants added, research also shows that young people who reported living in an accepting community, had access to LGBTQ-affirming spaces, or had social support from family and friends reported significantly lower rates of attempting suicide in the past year. “We urge coaches, educators and school administrators to seek LGBTQ-cultural competency training, implement zero tolerance policies for anti-trans bullying, and create safe, affirming environments for all transgender students on and off the field,” DeChants said.
O’Connor said her experiences on the athletic scene have been mostly positive. The politics of her community lean somewhat liberal, and she thinks it’s probably more supportive than some other areas of the country, though she noted the local library has received threats for hosting LGBTQ events. In addition to badminton, she also played baseball, lacrosse, volleyball, basketball and hockey. In the spring, she plans to become an assistant coach or manager for the girls’ badminton team at her old high school.
“When I played badminton, I never got any direct backlash from any coaches, competitors or teammates,” she said. “I had a few other teammates that identified as trans or nonbinary, [and] nearly all of the people I ever interacted with were super pleasant and treated me like any other normal person.” She added that transgender athletes “have aspirations. We have wants and needs. We have dreams. And at the end of the day, we just want to live our lives and be happy like everyone else.”
The Friday Five covers five stories in research that you may have missed this week. There are plenty of controversies and troubling ethical issues in science – and we get into many of them in our online magazine – but this news roundup focuses on scientific creativity and progress to give you a therapeutic dose of inspiration headed into the weekend.
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Here are the promising studies covered in this week's Friday Five:
- Research on a "smart" bandage for wounds
- A breakthrough in fighting inflammation
- The pros and cons of a new drug for Alzheimer's
- Benefits of the Mediterranean diet - with a twist
- How to recycle a plastic that was un-recyclable