Relation of Dietary Sodium (Salt) to Blood Pressure and Its Possible Modulation by Other Dietary Factors: The INTERMAP Study

Abstract

Available data indicate that dietary sodium (as salt) relates directly to blood pressure (BP). Most of these findings are from studies lacking dietary data; hence, it is unclear whether this sodium-BP relationship is modulated by other dietary factors. With control for multiple nondietary factors, but not body mass index, there were direct relations to BP of 24-hour urinary sodium excretion and the urinary sodium/potassium ratio among 4680 men and women 40 to 59 years of age (17 population samples in China, Japan, United Kingdom, and United States) in the INTERMAP (International Study on Macro/Micronutrients and Blood Pressure), and among its 2195 American participants, for example, 2 SD higher 24-hour urinary sodium excretion (118.7 mmol) associated with systolic BP 3.7 mm Hg higher. These sodium-BP relations persisted with control for 13 macronutrients, 12 vitamins, 7 minerals, and 18 amino acids, for both sex, older and younger, blacks, Hispanics, whites, and socioeconomic strata. With control for body mass index, sodium-BP-but not sodium/potassium-BP-relations were attenuated. Normal weight and obese participants manifested significant positive relations to BP of urinary sodium; relations were weaker for overweight people. At lower but not higher levels of 24-hour sodium excretion, potassium intake blunted the sodium-BP relation. The adverse association of dietary sodium with BP is minimally attenuated by other dietary constituents; these findings underscore the importance of reducing salt intake for the prevention and control of prehypertension and hypertension.

Clinical trial registration: URL: https://www.clinicaltrials.gov. Unique identifier: NCT00005271.

Keywords: blood pressure; diet; hypertension; potassium; sodium.

Figure 1

Mean blood pressure by quartiles of urinary sodium excretion adjusted for age, gender, and sample, education, physical activity, smoking status, history of cardiovascular disease or diabetes mellitus, family history of high blood pressure, use of special diet, use of dietary supplement, alcohol, animal protein, vegetable protein, cholesterol, total saturated fatty acids, total monounsaturated fatty acids, omega 3 fatty acids, omega 6 fatty acids, total trans fatty acids, total sugar, starch, total dietary fiber, caffeine: (A) systolic blood pressure (mm Hg) and (B) diastolic blood pressure (mm Hg) for 4,680 participants; (C) systolic blood pressure (mm Hg) and (D) diastolic blood pressure (mm Hg) for 2,195 US participants. Quartile cut-offs for urinary sodium (Na) excretion (mmol/24-h) were 145.96 (25^th percentile), 187.12 (50^th percentile), 236.47 (75^th percentile) for men and 118.83, 153.40, 196.08 for women and quartile cut-offs for urinary potassium (K) excretion (mmol/24-h) were 41.58 (25^th percentile), 53.60 (50^th percentile), 69.94 (75^th percentile) for men and 36.43, 46.48, 59.09 for women.