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Last week Mrs. Bremner was communicating to us from the American Heart Association Meeting about the importance of salt on blood pressure and health which led to a post about the topic which led to a lively discussion. David Colquhoun started out by pointing out that the graph showing a correlation between salt load and hypertension from the paper by Professor MacGregor could be accounted for by four data points. Mrs. Bremner countered by pointing out that they had re-analyzed the results without the four lowest data points and it was still significant. She subsequently pointed to another paper which summarizes clinical trials on the effects of salt reduction in the diet on health.
In this paper the authors point out that many studies that are used to argue that salt reduction has no effect on hypertension or health are studies in which the salt reduction only occurred of the course of one week, or involved acute salt depletion. The authors point out that one week is not long enough to evaluate the effects of salt reduction, and that acute salt reduction leads to an activation of the sympathetic nervous system, which leads to an artificial increase in blood pressure. Sounds good to me so far, guys.
They listed 17 trials of people with hypertension and 11 trials of people with normal blood pressure that were conducted for four weeks or more and had adequate salt reduction (4.6 g per day) as measured by excretion in the urine. People with hypertension had a 5 mm Hg point drop in systolic and 3 point drop in diastolic. People with normal blood pressure also showed a drop to a lesser extent. The authors note that this amount of salt reduction would result in a 14% drop in strokes and a 9% drop in heart deaths.
Clinical trials of dietary salt reduction and high blood pressure
Unfortunately noone has done a randomized trial of low salt versus high salt diet and it is unlikely to happen now due to ethical issues. Mrs. Bremner points out that increases in salt in the diet lead to a craving for salty food that causes a vicious cycle, which is one way people may become addicted to salty junk foods and snack foods.
Dr B.’s comment: It looks like cutting down on salt does lower blood pressure although a 14% relative reduction in cardiac events may not be that big of a deal in terms of absolute reduction of risk for a single individual. Salt may be just part of the problem with junk food. There was a study showing that people who eat in fast food restaurants three times a week have a greater than 90% risk of getting diabetes or heart disease and I need to find that reference again.
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The “mass media/press release” method of disseminating health information and research results is a serious detriment to the public’s understanding of issues, as well as (perhaps most consequentially) it’s confidence in research and recommendations.
It’s not particularly reasonable that the “average citizen” have the knowledge to evaluate the validity of new research claims. But the science and medical “journalists” who make a living reporting on it absolutely should have more responsible, critical reports.
Typically foods which are high in sodium are heavily-processed manufactured foods. Many are high in saturated fats and (decreasingly) in trans-fats plus food additives of dubious healthfulness. It’s an education to look at the McDonald’s or Burger King site and see what is in “broiled chicken”. There may be some other aspects of the food that contains salt which cause heart disease and diabetes.
One of the benefits of changing to a very low sodium diet is that it forces one to almost exclusively use “real” natural foods.
The blood pressure – sodium link can be easily proved by an individual with a less than perfect diet. Take your own blood pressure just after you wake up for a week or more to establish a baseline. After establishing a baseline, change your diet by eliminating fast foods, added salt, soy sauce, soups, snack foods, crackers, salted nuts, restaurant food, processed foods – anything that has a lot of sodium. Take your blood pressure after 1 month, 2 months, 6 months on the new plan and compare with pre-low-sodium baseline.
The longer I sustain a low sodium intake, the lower my BP goes. I have done “the experiment” on myself several times. After eating low sodium for several years, I did the reverse and started eating more sodium, only to see my BP rise back to previous levels (quite quickly). The maddening aspect is that it’s very difficult to sustain very low sodium intake for long periods because it’s almost impossible to eat in restaurants or with friends and it forces one to prepare all one’s own food.
Salt is very unhealthy for kidneys, there really is no doubt on that one. Of course that won’t affect the majority of the population, but for those who it will it is a big deal. Lots of folks have early stage kidney disease and don’t know it, if they reduce salt they may not progress to later stages. Dialyis From the Short End of the Needle has a lot on salt. http://www.billpeckham.com/from_the_sharp_end_of_the/
I just came across this observational study that did not find a correlation between salt intake and cardiovascular or all cause mortality
http://www.springerlink.com/content/51x08lvvv76v9204/?p=2c7629de0c124215ba7a9d69c50a30e7&pi=1
and here is a cochrane review that showed only a 1 mm reduction with diet change in systolic blood pressure in non hypertensive people. In patients with hypertension those with low salt diet were more likely to come off drugs and be ok than those on regulare diet.
http://mrw.interscience.wiley.com/cochrane/clsysrev/articles/CD003656/frame.html
http://junkfoodscience.blogspot.com/2008/06/traffic-tickets-for-salt-does-healthy.html