Salt's Effect on Blood Pressure Decreased by Physical Activity

The more physically active a person is, the less blood pressure (BP) rises in response to a high-salt diet, according to a new study.

Researchers at Tulane University School (New Orleans, LA, USA) compared 1,906 Han Chinese adults (average age 38) participating in the Genetic Epidemiology Network of Salt Sensitivity (GenSalt), a large project to identify genetic and environmental factors contributing to salt sensitivity. Study participants were put on two one-week diets, one low in sodium (3,000 mg/day) and the other high in sodium (18,000 mg/day); if a person's average systolic BP increased 5% or more from the low-sodium to the high-sodium regimen, the researchers labeled them as high salt-sensitive. Based on physical activity questionnaires, the researchers divided the participants into four groups ranging from very active to quite sedentary.

The results showed that the average increases in systolic BP after switching from low to high sodium, adjusted for age and gender, were 5.27 mmHg in the least active group, 5.07 mmHg in the next-to-lowest activity group, 4.93 mmHg in the next to highest activity group, and 3.88 mmHg in the most active group. Compared with the sedentary group, the odds of being salt sensitive, adjusted for age and gender, fell by 10% in the next-to-lowest activity group, 17% in the next-to-highest activity group, and 38% in the most active group. The study was presented at the Nutrition, Physical Activity and Metabolism/Cardiovascular Disease Epidemiology and Prevention scientific sessions of the American Heart Association (AHA), held during March 2011 in Atlanta (GA, USA).

"Patients should be advised to increase their physical activity and eat less sodium. Restricting sodium is particularly important in lowering blood pressure among more sedentary people,” said lead author Casey Rebholz, MPH. "The study needs to be repeated, but I suspect that the relationship between physical activity and salt sensitivity will apply to other populations.”

The GenSalt project is located in rural China since the homogeneous make-up of the population makes it more likely that genes influential to BP control will be identified. Siblings and their parents were invited to become involved in GenSalt if at least one sibling had prehypertension (blood pressure between 120/80 mmHg and 139/89 mmHg) or stage-1 hypertension (between 140/90 mmHg and 159/99 mmHg).

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