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How Does Excess Salt Affect the Immune System

A standard Western diet is commonly high in sodium or salt intake which has been noted as a contributing factor for cardiovascular disease and the development of high blood pressure. Fast foods, fries, chips, packaged foods (especially those that contain seasoning blends) are loaded with salt. The American Heart Association recommends consuming no more than 2.3g of salt per day, however, it’s been reported that less than 10% of the American population actually follows this advice.1

Although salt is related to water balance in the body (volume and fluid pressure), excessive or inadequate amounts of salt intake can affect the immune system and lead to inflammation and other poor health outcomes.

Salt Sensitivity of Blood Pressure (SSBP)

SSBP is a condition that occurs when changes in salt intake follow changes in blood pressure (ex. blood pressure increases as salt intake increases). This happens in about 25% of people who typically have normal blood pressure levels and about 50% in those who have high blood pressure (hypertension). There are also other factors known to increase SSBP including obesity, insulin resistance and aging overall. It’s important to address SSBP since it’s considered an independent risk factor of death due to cardiovascular disease.1

High-Salt Diets and the Gut Microbiome

When consuming dietary salt, the first major site of contact for absorption is in the intestines. The intestinal track is loaded with bacteria and immune cells called dendritic cells. These dendritic cells help scope out the area for pathogenic microorganisms, protecting you while also allowing “good” or helpful bacteria species survive and live there.

Salt intake has been shown to affect this gut microbiome – the population of bacterial species living along the gastrointestinal tract. Your gut bacteria are extremely sensitive to the foods you send down. What you eat can change the types of species and strains of bacteria that live and survive. Those gut bacteria are responsible for helping you absorb nutrients, send information to your brain and nervous system, and they influence inflammatory pathways. These effects can cause high blood pressure to develop and may even be linked to some autoimmune conditions.

Interestingly, in cases of hypertension, the gut seems to have an increase in the ratio of Firmicutes: Bacteroidetes bacteria. This same ratio pattern is seen in those with obesity and metabolic syndrome.1 High salt diets result in similar patterns of increased Firmicutes species compared to Bacteroidetes bacteria, linking dietary salt to both gut bacteria and high blood pressure.

Researchers have recently been questioning whether certain probiotic treatments can affect salt-induced high blood pressure. In one animal study, three weeks of a high salt diet led to increased blood pressure, but pressure was significantly reduced and normalized when these

mice were treated with a Lactobacillus probiotic strain.

Immune Reactions from High-Salt Diets

TH17 cells are immune cells that can promote high blood pressure and play a role in autoimmune reactions. It has recently been shown that high salt diets may increase this TH17 activity.2 High dietary salt alters immune function, driving inflammatory pathways. This can cause the release of inflammatory signalling molecules in the kidneys and blood vessels which promote high blood pressure.1

In humans, one preliminary study had healthy male volunteers on a high salt diet (about 14g per day) for two weeks.2 This salt challenge significantly increased blood pressure, increased TH17 cells, and led to the loss of gut Lactobacillus bacteria (a finding common with a Western diet).

In an animal study, researchers found that a high-salt diet increased blood pressure within three days, but also increased the adhesion of white blood cells to blood vessels in the eyes.3 Adhesion molecules in the kidneys were also elevated, which can affect kidney function. With all findings of this study combined, researchers concluded that having a high-salt diet and hypertension is more detrimental than having high-salt intake alone, but there are certain immune reactions that occur before salt-induced hypertension occurs or is even caught by your doctor.

For example, high-salt diets can suppress anti-inflammatory white blood cells (macrophages) and promote pro-inflammatory macrophages.3 How much salt does it take to do this? One study in healthy human adults found that higher monocytes were found on a diet of 12g per day (keep in mind that the AMA recommends a maximum of 2.3g per day and a single fast food meal contains 1.2g of sodium). Following up with a low salt diet (<5g of sodium per day), these effects were reversed.4

Should I Give Up Salt?

Although we’ve addressed the health detriments to too much salt, it should also be noted that a diet without any salt at all can also be detrimental. Sodium restriction diets have been associated with an increase in inflammatory molecules (C-reactive protein, IL-6 and TNF-alpha).3

Basically, the body needs some salt as sodium is a major component of many cellular processes, and acts as a transporter for molecules to get in and out of your body’s cells. Sodium regulates the uptake of sugars from your gut and the kidneys, it regulates calcium signalling, the action of neurotransmitters, pH balance, and the transportation of minerals like magnesium.

The bottom line is that your body needs salt, but the average consumption in a Western diet is typically way too high. Salt consumption should not exceed 5g (5000mg) per day (about one teaspoon), but recommendations for cardiovascular health are set much lower. The AMA recommends a maximum of at 2.3g (2300mg) per day, while Health Canada recommends 1g to 1.5g per day (1000-1500mg) for those over the age of one.

References

1. Elijovich F, Laffer CL, Sahinoz M, et al. (2020). The Gut Microbiome, Inflammation, and Salt-Sensitive Hypertension. Curr Hypertens Rep. 22(10):79

2. Wilck N, Matus MG, Kearney SM, et al. (2017). Salt-responsive gut commensal modulates TH17 axis and disease. Nature. 551(7682):585-589

3. Afsar B, Kuwabara M, Ortiz A, et al. (2018). Salt Intake and Immunity. Hypertension. 72(1):19-23

4. Yi B, Titze J, Rykova M, et al. (2015). Effects of dietary salt levels on monocytic cells and immune responses in healthy human subjects: a longitudinal study. Transl Res. 166:103–110

About The Author

Dr. Sarah Zadek is a licensed naturopathic doctor in Ontario with a clinical focus on women’s health, endocrinology and fertility. Sarah graduated from Nipissing University with an honours degree in biology after completing her thesis on genetics, oxidative stress and immune function. Her working background includes 14 years in pharmacy. Sarah is also an author and has written for multiple publications across North America including the NaturalPath, Naturopathic News and Review (NDNR), Naturopathic Currents, and Eco Parent Magazine online. Dr. Sarah Zadek is a naturopathic doctor with Conceive Health, practicing at Lakeridge Fertility in Whitby, and is a technical writer for Advanced Orthomolecular Research (AOR).

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