Effects of dietary salt levels on monocytic cells and immune responses in healthy human subjects: a longitudinal study

Abstract

Increasing evidence indicated that excess salt consumption can impose risks on human health and a reduction in daily salt intake from the current average of approximately 12 g/d to 5–6 g/d was suggested by public health authorities. The studies on mice have revealed that sodium chloride plays a role in the modulation of the immune system and a high-salt diet can promote tissue inflammation and autoimmune disease. However, translational evidence of dietary salt on human immunity is scarce. We used an experimental approach of fixing salt intake of healthy human subjects at 12, 9, and 6 g/d for months and examined the relationship between salt-intake levels and changes in the immune system. Blood samples were taken from the end point of each salt intake period. Immune phenotype changes were monitored through peripheral leukocyte phenotype analysis. We assessed immune function changes through the characterization of cytokine profiles in response to mitogen stimulation. The results showed that subjects on the high-salt diet of 12 g/d displayed a significantly higher number of immune cell monocytes compared with the same subjects on a lower-salt diet, and correlation test revealed a strong positive association between salt-intake levels and monocyte numbers. The decrease in salt intake was accompanied by reduced production of proinflammatory cytokines interleukin (IL)-6 and IL-23, along with enhanced producing ability of anti-inflammatory cytokine IL-10. These results suggest that in healthy humans high-salt diet has a potential to bring about excessive immune response, which can be damaging to immune homeostasis, and a reduction in habitual dietary salt intake may induce potentially beneficial immune alterations.

Sodium chloride inhibits the suppressive function of FOXP3+ regulatory T cells

“…Of note, recent studies in patients with autoimmune diseases indicated that higher salt intake is associated with increased clinical and radiological disease activity in MS patients and with increased risk of developing rheumatoid arthritis (28,29). Moreover, a recent longitudinal study under highly controlled conditions in humans indicated that changes in dietary salt levels could significantly impact cellularity of cells of the innate immune system and secreted levels of pro-and antiinflammatory cytokines such as IL-6, IL-23, and IL-10 in vivo (30). Besides raising interstitial sodium content, high-salt diets potentially exert direct effects on lymphocytes in gut-associated tissues and within the intestine (25).…”

Western lifestyle and immunopathology of multiple sclerosis

“…These findings were also accompanied by a higher exacerbation rate in patients with medium and high sodium intake compared with the normal‐intake group 76. Interestingly, there is a positive correlation between the amount of salt consumed and IL‐17 plasma levels in healthy individuals 83. However, a recent large European–Canadian trial study in MS patients treated with interferon‐β1b did not find any association between salt intake and MS activity or progression in this cohort 84.…”

“…demonstrated in a long‐term longitudinal study that there is a strong positive correlation between serum monocytes and dietary salt intake in healthy donors. Interestingly, high salt intake was associated with increased levels of IL‐6 and IL‐23 and decreased levels of IL‐10, thus creating a milieu that promotes T H 17 differentiation 83. Furthermore, 1 week of high salt diet in healthy volunteers resulted in expansion of nonclassical CD14 + CD16 + monocytes and monocyte–platelet aggregates with enhanced reactive oxygen species production by monocytes 89…”

Salt and Pregnancy Complications: A Proposal for Future Research

“…Yi et al [26] found a higher number of monocytes in the blood of healthy individuals with high dietary salt intake (12 g/d) than the individuals with normal dietary salt intake. It is of interest that reducing salt intake led to increased production IL-10 and decreased production of IL-23 and IL-6 by lymphocytes [26].…”

“…It is of interest that reducing salt intake led to increased production IL-10 and decreased production of IL-23 and IL-6 by lymphocytes [26].…”