FIGURE 3.

Hypertension-free survival probability by quintiles of Na/K ratio in the north (A), central (B), and south (C) regions in China, 1991–2009. Survival probabilities were adjusted by sodium intake, energy intake, age, sex, education, income, region, BMI, physical activity, smoking status, and alcohol consumption. The macro %EMICM in SAS 9.2 (SAS Institute) was used to compute the survival curves. Region had a significant interaction with the effect of the Na/K ratio on the risk of hypertension, with significant effects in both the overall sample and each region. In the third through the fifth quintiles of the Na/K ratio, there was a significantly higher HR for hypertension than for the lowest ratio quintile (P < 0.001 by flexible parametric models). Na/K ratio, the ratio of sodium to potassium.