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Harmful effects of salt in the diet.

Discussion in 'Science' started by doublehelix, Sep 2, 2011.

  1. I know that there is plenty of advice on how much salt we should eat due to its supposed tendency to raise blood pressure. However is this accepted as being proven? And if so, is the magnitude of increase of significance. (I don't mean statistical significance, I mean medical significance.)
    Also, how could researchers investigate the effect of salt on blood pressure and eliminate the placebo effect? We can taste salt in our food. The subjects being given a high salt diet would know, and this itself might cause their measured blood pressure to be higher. The subjects with a low salt intake would be expecting low blood pressure.
     
  2. I know that there is plenty of advice on how much salt we should eat due to its supposed tendency to raise blood pressure. However is this accepted as being proven? And if so, is the magnitude of increase of significance. (I don't mean statistical significance, I mean medical significance.)
    Also, how could researchers investigate the effect of salt on blood pressure and eliminate the placebo effect? We can taste salt in our food. The subjects being given a high salt diet would know, and this itself might cause their measured blood pressure to be higher. The subjects with a low salt intake would be expecting low blood pressure.
     
  3. BelleDuJour

    BelleDuJour Star commenter

    There could be a placebo effect on blood pressure, much like having your blood pressure taken increases it by suggestion.
    However, the physiological effect of salt on blood pressure is well documented. I'll try to explain.
    When you eat salt is gets absorbed into the bloodstream. The more salt you eat, the saltier your blood gets. Now, control of water in the body is crucial to life. When the blood gets too salty, water enters the blood from the kidenys, other body tissues and the gut by mainly a process called osmosis. This movement of water into the blood continues until the blood is once again diluted and at it's normal salt concentration. All this extra water is absorbed by the blood vessels, but they cannot expand to accommodate it, hence the rise in blood pressure caused by extra volume of liquid being forced into the same volume blood vessels.
    This happens regardless of any placebo effect.
    I suspect that statistics will show the majority of people eating a high salt diet have higher blood pressures than those eating a low salt diet.
    IMO eating a balanced diet, with plenty of fresh fruit and veg and a minimum of processed food should equate to a diet low in salt.
     
  4. Thanks for your answer.
    Presumably the concentration of salt in the blood is also under control? So any increase in blood salt content would be temporary? And I was under the impression that blood pressure is also under homeostatic contol.

    A linkage between high salt diet and high blood pressure does not, of course, imply that one causes the other.
     
  5. phlogiston

    phlogiston Star commenter

    There was some research reported during the summer suggesting the link was less significant than previously thought (or maybe not significant).
    Personally I'm taking this with a pinch of salt.[​IMG]
    P
     
  6. briggs1209

    briggs1209 New commenter

    The evidence against salt has been based on several small studies and the links, whilst reasonable each time, do not seem to be significant.

    There was a really good article in Scientific American this June 'It's time to end the war on salt' which can be found here http://www.scientificamerican.com/article.cfm?id=its-time-to-end-the-war-on-salt

    The real research was done by the excellent cochrane collabaration. Their plain-english summary will take two minutes to read. The summary and full research can be found here http://www2.cochrane.org/reviews/en/ab003656.html

    To be frank, I have started using more salt since reading the material.
     
  7. Thanks, Briggs1209. The article in Sci Am is indeed readable. It also seems to confirm my suspicions. Pass the salt!
     
  8. Can you tell the difference between bread loaded with salt and that in which salt has been removed to the nth degree? I cant. (its been on the news this week). Hence running a conrolled experiment to negate the placebo effect from salt intake would be possible. However, the control of other variables would prove more difficult, and probably raise some ehtical issues, which, as long as you arent teachinf medical students, you dont need to worry about.
     
  9. Regarding the blinding...would introducing the salt via saline drip not solve that problem?
     

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