Interindividual variation in serum sodium and longitudinal blood pressure tracking in the Framingham Heart Study

BACKGROUND: Recent cross-sectional studies have suggested that higher serum sodium levels may be a marker of elevated blood pressure. It is unclear whether serum sodium levels are related to the risk of developing hypertension in the community. METHODS: We investigated the association of serum sodium with longitudinal blood pressure tracking and incidence of hypertension in 2172 nonhypertensive Framingham Offspring Study participants (mean age 42 years, 54% women). We defined an increase in blood pressure as an increment of at least one category (as defined by the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure), and incident hypertension as a systolic blood pressure of at least 140 or a diastolic blood pressure of at least 90 mmHg, or use of antihypertensive medications. Serum sodium was analyzed as a continuous variable, and as categories. RESULTS: Cross-sectionally, serum sodium was not associated with systolic or diastolic blood pressure (P exceeded 0.10). On follow-up (mean 4.4 years), 805 participants (37%, 418 women) progressed by at least one blood pressure category, and 318 (15%, 155 women) developed new-onset hypertension. In multivariable logistic regression analyses (adjusting for age, sex, baseline blood pressure, diabetes, BMI, weight gain and smoking), serum sodium was not associated with blood pressure progression (odds ratio per SD increment 0.93, 95% confidence interval 0.85-1.03), or with hypertension incidence (odds ratio per SD increment 0.94, 95% confidence interval 0.82-1.08). CONCLUSION: In our large community-based sample, serum sodium was not associated with blood pressure cross-sectionally, or with blood pressure tracking or hypertension incidence longitudinally.