A High Salt Diet Can Worsen Autoimmune Diseases

The average American’s daily sodium intake is 37% higher than government recommendations and nearly 300% higher than the estimated sodium intake of ancestral humans. Given the research showing the negative health impacts of even moderately elevated sodium intake, it’s no surprise that science has shown that a high salt diet can worsen autoimmune diseases. Let’s explore how those on an Autoimmune Protocol Diet may want to carefully consider their sodium intake.

Salt is everywhere today in our modern food environment. Over 50 percent of a typical household’s grocery spending goes into ‘ultra-processed’ foods which bring along with them a significant amount of salt (sodium chloride).¹

But, in evolutionary terms, it’s only been a staple in the human diet for a very short time.

Our ancestors survived on a diet of less than 1,000mg per day for millions of years, before the introduction of salt into the diet some 5,000 years ago as a method for preserving food.²

Today, the average intake of sodium in the general population is 3,400mg daily, much higher than the recommendation from the Dietary Guidelines for Americans, which says to consume less than 2,300mg per day as part of a healthy eating pattern.³

In fact, modern sodium intake can be as high an 8,000mg per day in some parts of the world, the overwhelming majority coming from processed foods and eating out in restaurants.⁴

Our current high salt intake is therefore in tremendous excess compared to our ancestral past. Is this a cause for concern for human health?

The most obvious problem is the effect of salt on blood pressure. The evidence from high-quality observational and interventional studies reveals that excessive salt intake is associated with hypertension.^5,6 It’s also widely accepted that high salt intake is linked with the development of cardiovascular disease, and it is heavily taxing on the kidneys with some evidence it plays a role in the progression of chronic kidney disease.^7,8

A lesser known adverse effect of excessive salt intake is its role in autoimmune conditions like rheumatoid arthritis.

High Salt Diets, Innate Immunity, and Autoimmune Conditions

The innate immune system is the body’s first line of defense, preventing the intrusion of foreign invaders. It responds to infection and other disturbances in homeostasis by activating the body’s inflammatory processes.

In 2009, a ground-breaking animal study found that excessive intake of salt increased skin concentrations of sodium. This increase activated macrophages of the innate immune system to clear the stored sodium through the lymphatic system.⁹ Macrophages, like many immune cells, can play multiple roles in the body; some macrophages (M1) are pro-inflammatory, while other macrophages (M2) are anti-inflammatory.¹⁰

The activation of anti-inflammatory (M2) macrophages has been shown to reduce the development of autoimmune disease.^11,12 The problem with a high salt intake is that it increases pro-inflammatory and decreases anti-inflammatory macrophages.^13,14

Why would this occur from an evolutionary standpoint?

It appears that infections increase sodium levels inside the cell, leading the local activation of pro-inflammatory macrophages to combat the intruding pathogen, while limiting it in the rest of the body. This phenomenon occurs at all key sites in the body – skin, kidneys, and genitourinary – where the body interfaces with the external environment.

In short, the immune systems response to increased sodium levels is an ancestral protection mechanism against foreign intruders at these locations.

High Salt Diet, Adaptive Immunity, and Autoimmune Conditions

The adaptive ‘seek and destroy’ immune system is also impacted by high salt intake. The specialized cells of the adaptive immune system are activated by the detection of foreign invaders into various T-cells – Th1, Th2, T_h17, etc. – in order to target specific intruders.

One important balance in the body is between pro-inflammatory T_h17 cells and anti-inflammatory T Regulatory (T_reg) cells. Activation of T_h17 has been implicated in numerous autoimmune kidney diseases and renal transplant rejection, while T_reg activity limits the progression of these conditions.¹⁵ Alarmingly, new research on high salt intake finds it increases T_h17 and reduces T_reg activity, thus potentially worsening autoimmune kidney diseases and likelihood of transplant rejection.^16,17

In fact, an imbalance between T_h17 and T_reg cells has been associated with multiple autoimmune conditions. Emerging research shows a high salt diet could exacerbate a variety of complex conditions, including; multiple sclerosis^18,19, inflammatory bowel disease^20,21, systemic lupus erythematosus^22,23, and acute kidney injury.^24,25

Sodium Can Trigger Autoimmune Response

The immune system attempts to maintain homeostasis by keeping a balance between pro- and anti-inflammatory cells. High salt diets promote the activation of both the innate and adaptive immune systems and favor a pro-inflammatory milieu. While under normal conditions, it helps clear infections at the local cellular level, the consequences a chronic pro-inflammatory state due to hypersalinity appears to promote the development of autoimmune disease.

It’s still unclear whether the dietary manipulation of salt can mediate these effects, however, the evidence appears to support a more conservative approach to salt intake. As the majority of salt intake comes from processed food consumption, it’s another great reason to limit your consumption and adopt a ‘food first’ approach consistent with a Paleo dietary eating pattern.

References

1. https://www.theguardian.com/science/2018/feb/02/ultra-processed-products-now-half-of-all-uk-family-food-purchases
2. Intersalt Cooperative Research Group. Intersat: an international study of electrolyte excretion and blood pressure. Results for 24-hour urinary sodium and potassium excretion. BMJ 1988;297:319-328.
3. https://www.cdc.gov/salt/pdfs/sodium_dietary_guidelines.pdf
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