Are you as-salting your immune system?

10 May 2021

As temperatures drop here in the southern hemisphere, and we edge into the winter cold and flu season, many people’s thoughts are once again turning to the question, ‘How can I support my immune system to keep me well?’ And right on cue, health food stores and pharmacies are pushing all manner of nutritional supplements and herbal remedies that are claimed to ‘boost immunity’, whatever that means.

Unfortunately, few of the people eager to pop these pills give much thought to how everything else that goes into their mouths each day might affect their immune function. And fewer still are aware of the harmful effect of one particular food additive that is practically ubiquitous in the food supply: salt.

Since 2015, a team of European researchers has been studying the effects of salt on the metabolism and activity of white blood cells, the front line combat troops of our immune system.

In a paper titled ‘Effects of dietary salt levels on monocytic cells and immune responses in healthy human subjects: a longitudinal study‘, the researchers studied the long-term effects of three different levels of sodium intake – 12 g, 9 g and 6 g per day, with each level of sodium intake maintained for an average of 50 days – on white blood numbers and immune system activity.

They had a very unique way of ensuring that the study participants were sticking to the prescribed sodium levels at each stage of the project: They had total control over all food and beverages provided to participants, who were training for a spaceflight mission to Mars!

It’s not often that scientists have access to a ‘captive’ population of humans to run experiments on (at least, if they want their experiment to get through ethics committee approval), but the Mars520 project – a controlled simulated spaceflight program in which 12 healthy young male volunteers agreed to spend 520 days in an enclosed habitat consisting of hermetically sealed interconnecting modules – provided the perfect opportunity to run a long-term study on the effects of varying sodium intake.

At the end of each phase of salt intake, the participants gave blood samples, which the researchers analysed for both the number and activity of the various types of white blood cells that play a role in our bodies’ defences against infection.

They found that both the percentage of white blood cells that were monocytes, and the actual numbers of monocytes, declined with lower sodium intake:

Monocytes are precursors to macrophages which patrol the body seeking out foreign invaders such as bacteria, as well as cellular debris, cancer cells, and dead or dying cells. Once macrophages encounter such targets, they live up to their name – Greek for ‘large eaters’ – by engulfing and digesting them with powerful enzymes.

So wouldn’t it be a good thing to have elevated numbers of monocytes coursing through one’s bloodstream? Unfortunately not. As the researchers point out,

Monocytes were not only more numerous when participants ate more salt; their cytokine release pattern when exposed to an invader was also markedly different. Monocytes that formed when participants were eating 12 g of salt per day released more inflammatory chemicals (interleukins 6 and 23) and less of a chemical that helps to control inflammation (interleukin 10).

This amped-up inflammatory response can lead to the cytokine storm that we’ve become familiar with in COVID-19, causing tissue damage that persists long after the infection has been mopped up by the immune system.

Not content with their discovery that sodium intake affected white blood cell formation and activity, the researchers designed more experiments to find out how the ubiquitous seasoning does its dirty work. Their findings have just been published in an article titled ‘Salt transiently inhibits mitochondrial energetics in mononuclear phagocytes‘.

Phagocytes include monocytes, the cells that were found to proliferate on a high salt diet, as well as neutrophils and eosinophils.

To carry out their vital functions, these workhorses of the immune system need energy. That energy is provided by mitochondria – tiny ‘power plants’ within each cell that convert glucose (blood sugar) into adenosine triphosphate (ATP), the universal currency of energy within all cells.

However, high concentrations of sodium reduce the mitochondria’s ability to produce ATP, leaving immune cells underpowered.

The researchers began by exposing immune cells to high sodium concentrations in vitro – that is, in a petrie dish in the lab. They observed compromised ATP production after just three hours of exposure to a salty environment.

But does high sodium intake in people affect immune cells’ energy metabolism? To find out, researchers recruited volunteers for two experiments.

In the first experiment, healthy male participants took tablets that contained six grams of salt, each day for 14 days. In the second, participants ate a pizza which contained a whopping 10 g of salt.

Blood samples drawn from participants confirmed both that the concentration of sodium in their blood plasma rose after high sodium intake, and that the energy metabolism of white blood cells was impaired by high sodium concentrations.

The pizza-eating experiment gave an indication of the duration of the salt effect on white blood cells: their energy metabolism was significantly inhibited at three hours post-pizza, but by eight hours, it had returned to normal.

That’s reassuring news for people who indulge in an occasional salty meal or snack, but not so much for those who eat processed food – the major source of dietary sodium, accounting for nearly 80% of the average person’s intake – on a regular basis.

Staples of the Standard Australian Diet (SAD), such as bread, cheese, processed meats, crackers, chips, tomato sauce, gravy mix, and convenience products including ready-made soups and meals, are all brimming with sodium… and don’t get me started about the insanely high levels of sodium found in fast food items such as burgers, fries and pizza!

The bottom line on salt and your immune system

Your immune system works hard every day to defend you against threats from both the outside – bacteria, viruses, parasites and foreign objects – and the inside – dead, dying and damaged cells.

While you certainly want your immune system to be capable of packing a punch against dangerous invaders, there’s a fine balance that must be struck between a robust immune response and an uncontrolled overshoot that causes tissue damage.

The current SARS-CoV-2 pandemic provides a salutary lesson in immune balance: the virus only proliferates for around a week, which means that severe and critical COVID-19 – which only begin well after viral replication has fallen off – is driven not by the virus itself, but by a dysfunctional immune response to the virus.

High sodium intake is not the only contributing factor to this aberrant immune response, but it’s one that can be addressed far more rapidly than almost all of the other contributing factors. You can stop the as-salt on your immune system by cutting sodium intake at your very next meal; losing excess body fat, lowering your blood pressure and reversing type 2 diabetes take a good deal longer!

If you are overweight or have a chronic disease that puts you at increased risk of serious illness from viral infection, NOW is the time to take action on it! Obesity, type 2 diabetes, hypertension and coronary artery disease are preventable and largely reversible with a wholefood plant-based diet and Lifestyle Medicine. Apply for a Roadmap to Optimal Health Consultation today; online and in-person appointments are available.