1. Higher sodium intake in patients with multiple sclerosis was associated with an increased risk of clinical exacerbations.
2. Patients with a high-sodium intake had an over 3-fold greater chance of developing new MRI lesions.
Evidence Rating Level: 2 (Good)
Study Rundown: Multiple sclerosis (MS) is a potentially devastating neurological disease characterized by an immune response against the central nervous system that causes demyelination of neurons. In addition to genetic factors, it has been suggested that environmental factors such as vitamin D levels and Epstein-Barr virus infections may play a role in the disease course of MS. High-sodium diets in mice were found to be associated with more aggressive courses of immune encephalomyelitis, the animal model for MS. This study looked at Argentinian patients with relapsing-remitting MS and found a positive correlation between sodium intake and clinical exacerbations as well as radiologic findings. Patients with average (2-4.8 g/day) and above average sodium intake (≥4.8 g/day) had an exacerbation rate nearly 3 and 4 fold higher, respectively, than those in the baseline group (<2 g/day). In addition, the higher sodium intake groups had a roughly 3 fold increased risk of developing new MRI lesions.
The study’s strengths lie in its multivariate models which adjusted for many confounding factors as well as a second cross-sectional analysis in a different subset of 52 patients that yielded similar results. Its limitations include an inability to exclude confounders such as stress and commensal microbiota in addition to a relatively small cohort size. Further, individuals with lower sodium diets may have healthier lifestyles and better compliance overall, skewing the results in their favor. This study provides a nidus for further work and elucidation of the relationship between sodium, the Th17 cells modulated by sodium, and their ultimate relationship with MS.
Relevant Reading: Environmental factors and multiple sclerosis
In-Depth [prospective cohort]: This study was a prospective, cohort analysis of an initial 70 Argentinian patients with relapsing-remitting MS. Patients’ sodium intake was estimated from spot urine sodium excretion using the Tanaka equation. Clinical exacerbations of MS were defined as the development of new symptoms or worsening of pre-existing symptoms as determined by neurological examination. Periodic MRIs were also obtained to monitor radiological findings of active disease. Compared with the baseline sodium intake group, <2 g/day, the average intake group, 2-4.8 g/day, and the above average intake group, ≥4.8 g/day, had an exacerbation rate 2.75 (CI95%, 1.3-5.8) and 3.95 (CI95%, 1.4-11.2) fold higher than the baseline group (p<0.001 for trend). In addition, these two patient groups had a 2.86 (CI95%, 1.5-5.4) and 3.42 (CI95%, 1.4-8.6) fold increased risk, respectively, of developing new MRI lesions. The above average intake group had, on average, 8 more T2 MRI lesions (p<0.005) than the baseline group. A repeat cross-sectional analysis in a separate group of 52 MS patients had similar results with a positive correlation between salt intake and MS severity.
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