Reducing Sodium Reduces Blood Pressure

It's worth saying again: medicine is not like math. Remember back in Algebra class where if A = B and B = C, then A = C? One of the reasons that we do research in as large a group of people as we can is because not all people's bodies react the same way to certain things. More people in a study is better because it's easier to see how most people will react. This is why the plural of anecdote is not data. Which is to say, one person's experience can not be said to be proof that something is true for everyone. If, out of 1,000 people (for example), the vast majority of people are having a certain reaction under the same circumstances, however... that starts to look like proof (and even then more research may be needed).

While reducing sodium intake to improve blood pressures is considered obvious because it's basic biochemistry, it's important to remember that sometimes medicine doesn't work as straightforwardly as all that. Years ago there hadn't been many studies that demonstrated that a lower sodium diet would actually translate directly to a lower blood pressure.

Fortunately, back in 1997 the American Journal of Clinical Nutrition published a study that pooled the results of thirty-two smaller studies that looked at the connection between salt in the diet and blood pressure (1997;65(suppl):643S-51S). Essentially they asked that basic question: "Does reducing sodium intake reduce blood pressure?"

The studies they included in their pooled results had to meet certain criteria, including participants being randomly assigned to the test group; blood pressure measurements of both systolic and diastolic measures; not using blood pressure medications for some participants and not others; objective reporting of sodium intake (as opposed to food records, which might not be accurate); adult participants; and, finally, when the participants reduced their sodium intake, that intake had to be to levels that were actually reasonable to achieve for people living in the real world.

That's a pretty tight set of criteria and led to a total of a little over 2,600 participants. Those participants who had high blood pressure at the start of the studies reduced their sodium intake by an average of almost 1800 milligrams per day. That might sound like a lot, but remember that the average intake of salt for men in the United States is about 10,000 milligrams. That's reducing your sodium intake by only 18%! These folks with high blood pressure reduced their systolic blood pressures (the top number) by almost 5 points, and their diastolic blood pressure (the bottom number) by 2.5 points. That's something your doctor would consider significant.

Similarly, those whose blood pressure was normal at the start of their studies reduced their salt intake by about the same amount, and also saw their blood pressures reduced by meaningful amounts: a little over 2 points for systolic and about 1.5 points for diastolic. Is this an amount that matters? Definitely: a drop of just 3 points in our country's average systolic blood pressure means 11% fewer strokes, 7% fewer incidents of heart disease (including heart attack), and 5% fewer deaths from all causes.

What this means for you

The participants in these studies did not have to cut their salt intake by very much to see an improvement in their blood pressure. And it's easier than you might think to reduce the salt in your diet: here are 3 Easy Steps to a Low Sodium Diet.

First posted: August 15, 2012