Salt and blood pressure

Someone claimed to me that reduced salt is important in regulating blood pressure in only about 20% of all people. A Wiki article, http://en.wikipedia.org/wiki/Hypertension, see under Prevention, says that reducing salt intake helps in about 33% of patients, but it seems it helps prevent it since it is in that section.

Can anyone provide STD on the subject? I am not asking for medical advice; I just want to know the facts. I will be asking an ethical question on this in IMHO, but here I am just asking the facts.

A high level of salt in the blood causes the body to retain water, which increases blood volume, which increases BP.

In someone without high BP, a fully functioning pair of kidneys, and that drinks plenty of fluids, you don’t really have to worry about your sodium intake. However, if you do have high BP, limiting your sodium intake will help lower your BP.

But, a low salt diet will only lower your BP by a little bit. I forget the exact number, but at most maybe lower it by about 10/5 mmHg. So, it might help you from going from pre-hypertension to hypertension, but won’t help you if you have a really high BP.

This looks like it’s going to be a research sort of day, so since I’m going to be hanging out on PubMed anyways…

I couldn’t check the paper cited on Wiki* for the “only 33% respond” figure, since the article was in German… But I have found a number of meta-reviews. This one dates back a while, and it generally states that reduced sodium intake results in:

Another single study, looking at the effects of one particular low-sodium diet, found that:

A more recent meta-review is consistent with the other two citations, though it adds some more details and qualifications:

But in all of those studies, I haven’t come across anything that would support the idea that a low sodium diet has no effect on a large majority of hypertensive patients. That may be an artifact of how you define “hypertensive” – it’s a somewhat arbitrary line. The AMA defines hypertension as having a systolic blood pressure above 140. So, it might depend on how you slice the data and define your outcomes. For example, you could have a study that observes a consistent 5 mm hg drop in blood pressure. But if a majority of subjects start with a blood pressure above 145, you could also legitimately state that that those patients dropped from “hypertensive” to “still hypertensive”. That could be easily misinterpreted by some random wiki editor as being equivalent to “low salt diet doesn’t help most people”. Which is bogus, since all of the trials I’ve seen so far indicate that reducing sodium results in a statistically and clinically significant reduction in blood pressure.

After doing a bit more research, there’s a review that looks at the variation in normotensive patients. That is, if you take healthy population and feed them increased or reduced sodium, some fraction will be insensitive to the change (and won’t see any changes in blood pressure), while another fraction will be hypersensitive to dietary sodium. That’s not the same as what you quote from wiki, however.

*I’m starting to realize that, while wiki citations are usually reliable, they’re usually a very small and selective subset of actual research on the topic. I think that means that one wiki contributor that isn’t familiar with the field will read a single paper, and stick that citation in, so you don’t really see the whole context. In my subfield, for example, wiki has a not-horrible article on the topic. But the citations represent a really tiny and non-representative sample of the research – just a single paper, which is presented by the wiki editor as definitive. But it’s just one small part of the story, and the conclusions from the entire field are really spread over dozens of papers.

Yeah, reducing sodium without changing anything else won’t do a whole lot. But if you combine that with exercise and weight loss and stress reduction, and you can see some pretty dramatic results.

In medicine, “STD” is Sexually Transmitted Disease, and I have no advice there…

Salt intake and hypertension is a subject of vast amounts of research and most of it is available somewhere on the web. Among the things to consider when you sort out whether or not decreasing sodium intake is helpful or not is whether you are normo- or hypertensive to begin with and whether or not you are in a “salt-sensitive” group.

For example, African Americans have typically been considered to be more salt-sensitive. As an example : “In this study, hypertensive AA women experienced a 23-mm Hg increment in SBP, and normotensive AA and white, as well as hypertensive white women, experienced a 13- to 15-mm Hg increment. Thus, excessive salt ingestion is an important modifiable risk factor for elevations in SBP in both AA and white postmenopausal women. Our original hypothesis was that higher Na+i in AA was mechanistically related to a greater prevalence of Salt Sensitivity in AA. This remains a possibility, because we observed that SS and salt-intermediate AA had a significantly higher Na+i and Na+i-K+i ratio than did the corresponding white groups…”

The current research seems to focus on salt sensitivity; it may be that this, rather than the consequent hypertension itself, is what promotes secondary hypertensive end-organ disease. And how likely you are to be salt sensitive may depend on what group you belong to. See here for example, for an article on the prevalence of a variant of the ACE gene in African Americans.

In short, if you can excrete sodium well, you are probably not going to have to worry about salt intake. Lots of ongoing research trying to figure out who, exactly, that is.

It doesn’t suprise me in the least that different people would respond to a low-salt diet differently. We all have different body chemistries, and genetic differences would surely come into play.

I have pretty dang low BP (it often won’t register a 3-digit # for either the top or bottom number) and that trait runs, heavily, in my mom’s side of the family. So I’d be willing to bet that if my aunts and I were in one of these studies, we might skew the numbers a little bit.

(And yes, I drink a ton of water every day, more than almost any non-athlete I know. The last time a nurse took my BP reading she tut-tutted at me a bit and told me I need to drink more water. I was like, “Lady, if only you knew …”)

Sorry, I meant TSD. As for the quote, it doesn’t come up in German on my browser. Here is the quote:

The person who gave me the 20% figure was my daughter-in-law, a family physician.

I hear that kind of statement all the time, and it sounds pretty meaningless to me, like the commercials that say “This pure-carb cereal is really nutritious as part of this healthy breakfast!” (which includes juice, milk, an egg, and who knows what all). Sodium gets a lot of hype, while the other factors are seemingly only mentioned as an afterthought.

The question I have is what results we could get for each of the other factors alone, and in their various combinations. Could we end up saying “Exercise without changing anything else won’t do a whole lot. But …”?

I don’t know statistics on this, however, there are plenty of people I’ve seen in practice that have lost a large amount of weight and been able to be taken off their Hypertension medication and their Diabetes Type II medications. These are the two main medical conditions that some people can control through lifestyle choices alone, without medication.

Thanks, Hirka. Anybody else?

(I guess I should say that my BP is fine, and I’m not looking for medical advice. I’m just curious about the relative benefits of the different factors.)