Association of estimated sodium and potassium intake with blood pressure in patients with systemic lupus erythematosus

Sodium and potassium intake are modifiable determinants of hypertension in the general population but have not been studied in patients with systemic lupus erythematosus (SLE). We examined the relationship between urinary excretion of sodium and potassium, as an estimate of intake, and blood pressure in patients with SLE. We studied 178 SLE patients and 86 controls, matched for age, sex, and race. Urine sodium (Na⁺) and potassium (K⁺) were measured by flame photometry. Blood pressure was the average of two resting measurements. The associations between systolic (SBP) and diastolic blood pressures (DBP) and estimated 24-hour urinary Na⁺, K⁺, and Na⁺:K⁺ ratio were tested. The estimated mean 24-hour urinary K⁺ excretion was lower, and the Na⁺:K⁺ ratio was higher in patients with SLE than controls. There were no significant differences in the estimated 24-hour urinary Na⁺. In patients with SLE, a higher urinary Na⁺:K⁺ ratio was associated with higher SBP (β coefficient = 4.01, p = 0.023) and DBP (β coefficient = 4.41, p = 0.002) after adjusting for age, sex, and race. SLE patients had significantly lower estimated 24-hour urinary K⁺ and higher estimated 24-hour urinary Na⁺: K⁺ ratio than controls. The urinary Na⁺:K⁺ ratio was significantly associated with SBP and DBP.