This study presents an extensive analysis of the effects on blood pressure (BP) of changes in sodium intake over a wide array of subgroups, including joint subgroups defined by age and hypertension status, race or ethnicity and hypertension status, and gender and race or ethnicity. Participants were given 3 levels of sodium (50, 100, and 150 mmol/2,100 kcal) for 30 days while consuming the Dietary Approaches to Stop Hypertension (DASH) diet (rich in fruits, vegetables, and low-fat dairy) or a more typical American diet. Within each diet and subgroup, there was a general pattern such that the lower the sodium level, the greater the mean reduction in BP. Sodium reduction from 100 to 50 mmol/2,100 kcal generally had twice the effect on BP as reduction from 150 to 100 mmol/2,100 kcal. Age had a strong and graded influence on the effect of sodium within the typical and DASH diets, respectively: -4.8 and -1.0 mm Hg systolic for 23 to 41 years, -5.9 and -1.8 mm Hg for 42 to 47 years, -7.5 and -4.3 mm Hg for 48 to 54 years, and -8.1 and -6.0 mm Hg for 55 to 76 years. The influence of age on the effect of sodium reduction was particularly strong in nonhypertensive patients: -3.7 mm Hg systolic for <45 years and -7.0 mm Hg for >45 years with the typical diet and -0.7 and -2.8 mm Hg with the DASH diet. Reduced sodium intake and the DASH diet should be advocated for the prevention and treatment of high BP, particularly because the benefits to BP strengthen as subjects enter middle age, when the rate of cardiovascular disease increases sharply.