The role of body mass index in the association between dietary sodium intake and blood pressure: A mediation analysis with NHANES

Background and aims: Recent research demonstrated that obesity and high dietary sodium intake, the two established risk factors for hypertension, were associated with each other. The objective was to investigate the potential indirect effect of sodium intake on blood pressure via body mass index (BMI).

Methods and results: Using ten years data from US NHANES (2007-2016), the study included adult participants (>20 years old) who were not taking antihypertensive medications and without baseline diseases (n = 12,262). BMI was modelled as the mediator of sodium intake on systolic and diastolic blood pressure, adjusted for age, sex, socioeconomic status, smoking, drinking, physical activity, calorie intake, fluid intake and potassium intake. Mediation analysis was performed to evaluate total effect, direct effect and indirect effect via BMI. Subgroup analyses based on three age subgroups (20-40, 41-60 and ≥61 years old) were performed. The mean age was 39.29 (13.4) years and 53.1 (0.45) % were males. The mean BMI was 27.8 (6.20) kg/m². Overall, 1 g/d increase in sodium intake was associated with an increased systolic blood pressure by 0.36 (95% confidence interval 0.14 to 0.58) mmHg, with a direct effect (0.14 (0.09-0.19)) and an indirect effect via BMI (0.23 (0.02-0.44)). The indirect effect was mainly observed in participants ≤60 years old.

Conclusion: Sodium intake showed both direct effect and indirect effect (via BMI) on systolic blood pressure in US NHANES. The findings provide evidence for combining sodium restriction and weight reduction measures for prevention of hypertension. Cautions should be taken when generalizing the findings to other populations with lower average BMI.