Is the association between salt intake and blood pressure mediated by body mass index and central adiposity?

To assess the amount of salt intake among normotensive (NT) and prehypertensive (PHT) subjects and to determine whether the association between salt intake and blood pressure is correlated with body weight and waist circumference (WC) or is independent.

A total of 806 NT and PHT subjects from Isfahan Healthy Heart Program (IHHP) were enrolled in the study. A standard questionnaire was used to assess sociodemographic characteristics. The amount of salt intake was measured by the 24-hour urine collection method. Blood pressure, height, weight, and WC were measured based on standard protocols.

The mean ages (± SD) of NT and PHT subjects were 35.9 (± 11.9) and 44.7 (± 12.5) years, respectively (P < 0.001). The mean values of body mass index (BMI) and WC were greater among PHT than NT subjects (BMI: 27.9 ± 3.8 vs. 25.1 ± 4.3 kg/m2; P < 0.001 and WC: 90.2 ± 8.6 vs. 81.2 ± 11.2 cm; P < 0.001, respectively). PHT subjects had higher amount of salt intake than NT ones (10.3 ± 6.2 vs. 12.7 ± 7.1 g/d, respectively; P = 0.003). Odds ratio (OR) for being PHT increased significantly across the tertiles of salt intake in crude model and sociodemographic- adjusted model. Further adjustment for BMI and WC values weakened the OR for being PHT and showed nonsignificant trend (OR (and 95% CI) for BMI across tertiles of salt intake: 1, 1.26 (0.59 - 2.69), 1.89 (0.93 - 3.81); P = 0.063 and OR (and 95% CI) for WC across tertiles of salt intake: 1, 1.22 (0.58 - 2.57), 1.79(0.89 - 3.56); P = 0.082).

The findings of this study suggest that the association between salt intake and blood pressure is related to body weight and WC.