Now a new study shows that one appears to influence the other.
Specifically, physical activity appears to help keep blood pressure from climbing after people eat eye-popping amounts of salt -- 18,000 milligrams a day to be exact. That's about 10 times the recommended daily intake for sodium. As a visual aid, picture 18 salted soft pretzels like the kind sold at mall food courts.
That's much more than most people ever come close to, so some experts question whether the findings of the study could be applied to the real world.
"Because the high salt part of this was so high salt, I'm not sure you can gain any insight into what you can do on a daily basis, eating a normal diet," says A. Marc Gillinov, MD. Gillinov is a staff cardiac surgeon at the Sydell and Arnold Miller Family Heart & Vascular Institute at Cleveland Clinic, in Ohio.
But Gillinov also says that the study is interesting because it is among the first to look at the relationship between physical activity and salt sensitivity and that it adds to what's already known about how to keep blood pressure within healthy limits.
"The exact mechanism by which salt influences blood pressure is not completely worked out," he tells WebMD. "But there's no question that over the course of years, the more salt you eat, the more likely you are to get high blood pressure as you get older, as you get to be a middle-aged or older adult."
Physical Activity and Salt Sensitivity
For the study, which was presented at the American Heart Association's Nutrition, Physical Activity and Metabolism/Cardiovascular Disease Epidemiology and Prevention 2011 Scientific Sessions,researchers recruited more than 1,900 Chinese adults with a family history of prehypertension or stage 1 hypertension (blood pressure between 140/90 and 159/99 mmHg). The average age of study participants was 38.
They then had participants follow two one-week diets. One diet was 3,000 milligrams of salt a day and the other was 18,000 milligrams a day.
If participants' blood pressure rose by 5% from the lower to higher salt weeks, they were considered to be salt sensitive.
Researchers also looked at how much physical activity the participants reported on questionnaires.
They found that the more physical activity a person got, the less likely they were to be sensitive to salt.
Study participants in the group that got the most physical activity had a 38% lower risk of being salt sensitive compared to those who got the least amount of physical activity.
The researchers, who were from China and Tulane University in New Orleans, said that their results needed to be repeated, but if other studies could duplicate the finding, that would point to a need for sedentary people, in particular, to eat a low-salt diet.
Even better, Gillinov says, would be for physically inactive people to get moving and watch their sodium.
"These are two things that affect blood pressure, salt intake and exercise, and for your health and for your heart, do your best on both fronts."
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