medwireNews: Urinary sodium-to-potassium (Na/K) ratio is independently and positively associated with disease activity and hypertension in people with rheumatoid arthritis (RA), Japanese study findings indicate.
This suggests that “dietary modifications such as salt restriction and potassium supplementation should be investigated as a potential candidate for attenuating both disease activity and hypertension in RA patients,” write Hiroto Minamino, from Kyoto University, and colleagues in Arthritis Research & Therapy.
They report that a third of the 336 participants (mean age 62 years, 83% women) from the Kyoto University Rheumatoid Arthritis Management Alliance cohort had hypertension, and their disease activity levels were generally low, with a mean DAS28-ESR of 2.4 points.
The mean urinary Na/K ratio, which was used as a simplified index of dietary salt loading, was 2.60 and the mean estimated daily salt intake, calculated with Tanaka’s formula, was 7.8 g.
When patients were categorized into tertiles of urinary Na/K ratio, the researchers found that the prevalence of hypertension as well as systolic and diastolic pressure increased significantly with increasing urinary Na/K ratio, as did DAS28-ESR and DAS28-CRP.
Other factors that increased significantly in line with the Na/K ratio included age, BMI, estimated glomerular filtration rate (eGFR), prednisolone use, and the proportion of men. Conversely, methotrexate use decreased significantly with increasing Na/K ratio.
When the researchers adjusted the data for age, sex, and smoking status they found that the urinary Na/K ratio was significantly and positively associated with the prevalence of hypertension (odds ratio=1.34).
Urinary Na/K ratio was also independently and positively associated with DAS28-ESR after adjustment for covariates related to disease activity, including age, sex, smoking status, BMI, rheumatoid factor, anti-cyclic citrullinated peptide antibody levels, current therapeutics, and eGFR.
And the relationship remained significant in subanalyses where participants were grouped by sex and prednisolone use.
Minamino and co-authors conclude that “urinary Na/K ratio may be useful as an indicator of hypertension in the RA population as it is in the general population.”
However, they caution that the “cross-sectional study does not imply causation, and there is a possibility of reverse causality, where RA disease activity alters dietary habits resulting in increased salt in-take.”
They add: “The long-term effect of urinary Na/K ratio on hypertension and RA disease activity is also still unknown.”
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Arthritis Res Ther 2021; 23: 96