Naked Science Forum
Life Sciences => Physiology & Medicine => Topic started by: thedoc on 25/05/2016 16:21:45
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How much salt is safe to eat, and what does too much do to your body?
Read a transcript of the interview by clicking here (http://www.thenakedscientists.com/HTML/interviews/interview/1001833/)
or [chapter podcast=1001355 track=16.05.24/Naked_Scientists_Show_16.05.24_1005213.mp3](https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.thenakedscientists.com%2FHTML%2Ftypo3conf%2Fext%2Fnaksci_podcast%2Fgnome-settings-sound.gif&hash=f2b0d108dc173aeaa367f8db2e2171bd) Listen to it now[/chapter] or [download as MP3] (http://nakeddiscovery.com/downloads/split_individual/16.05.24/Naked_Scientists_Show_16.05.24_1005213.mp3)
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Doesn't answer the obvious question, that if my blood pressure if excellent, should I still shy away from salt?
I would say crisps, but most of the crisps have replaced salt with flavourings, so the salt content is way down on what it use to be.
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Your body needs both sodium and chloride ions to function properly. However, it is easy to satisfy those needs, and excess salt can lead to problems. Everybody's needs and limits are slightly different, but in general there is a very wide window of healthy salt intake.
I will point out that "low sodium salt" contains significant amounts of potassium chloride (which your body also needs) but has a much smaller window for healthy intake (oral LD50 of KCl is about 3g/kg vs about 12g/kg for NaCl). Too much potassium can cause heart problems...
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The podcast mentioned a "target" salt intake of 6g per day; it also mentioned that in the UK, men average about 9g/day, and women 7g/day (from memory).
That target sounded a little high to me.
Australian recommendations are that 1.1-2.3g of salt per day is medically adequate (but Australians average about 10g/day!). See: http://www.nutritionaustralia.org/national/frequently-asked-questions/salt-and-hypertension
So it seems that the "target" is a target to get down below, not a target to aim at.
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Medical textbooks suggest that if your kidneys are working, and you ingest a reasonable amount of potassium along with the sodium, you are unlikely to eat a harmful quantity of salt because your tongue will tell you to stop and your kidneys will excrete the excess. Blood is isotonic with sea water, so everything will taste pretty disgusting before it begins to leach water from your body. But who cares about medical textbooks when the government tells you that salt is bad for you?
Apropos "Lo Salt": I use it to demonstrate natural radioactivity. Not only is KCl a favourite covert murder weapon, it's also radioactive!
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Apropos "Lo Salt": I use it to demonstrate natural radioactivity. Not only is KCl a favourite covert murder weapon, it's also radioactive!
Yes, I considered mentioning the radioactivity in my first post on this thread, but opted against it in case someone didn't get my sarcastic claim that it was dangerous. Detecting the decay of 40K in Low Sodium salt is an excellent high school/undergraduate demonstration--I wish more people had seen/done it...
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Doesn't answer the obvious question, that if my blood pressure if excellent, should I still shy away from salt?
I would say crisps, but most of the crisps have replaced salt with flavourings, so the salt content is way down on what it use to be.
It seems that there is a chronic rise in blood pressure with increasing salt burden over time. No one knows why, but salt does appear to affect endothelial function (lining of blood vessels), which might be part of the reason. The evidence is substantial that genetically-matched individuals who are / are not exposed to salt intake have higher and lower blood pressures respectively, as they age.
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I've often wondered whether such correlations as salt/blood pressure and smoking/cancer have a more subtle element to them.
Given a genetically matched pair, i.e. identical twins, why would one habitually consume significantly more salt, sugar, tobacco, alcohol, whatever.... than the other? If we exclude genetics, it must be environment. So who eats lots of snack foods and smokes a lot? My first guess would be the person with the most stressful life. Perhaps this can account for the anomalies of those heavy users who live to a ripe old age "against the odds".
An old colleague used to open his lectures on heart disease by pointing out that the French smoke more, drink more, and eat more fat than the British, but have a lower incidence of cardiovascular death. Why? Because they enjoy smoking, drinking and eating, and don't worry about rules, regulations, tax deadlines, government health warnings, working hours, or any other sources of stress.
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Only excess salt in your body is bad, your body needs salt to sustain its life.
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Given a genetically matched pair, i.e. identical twins, why would one habitually consume significantly more salt, sugar, tobacco, alcohol, whatever.... than the other? If we exclude genetics, it must be environment. So who eats lots of snack foods and smokes a lot? My first guess would be the person with the most stressful life. Perhaps this can account for the anomalies of those heavy users who live to a ripe old age "against the odds".
You're right, Alan, that there are lots of potential confounding factors, but the Intersalt study (http://ajcn.nutrition.org/content/65/2/626S.abstract) addressed this by including groups who are ancestrally related and inhabit similar environments but have different dietary practices ie one group adds seawater to cooking, the other does not.
This found the relationship alluded to above: dietary salt burden is linked to blood pressure elevation with age.
I absolutely agree with you though that there are lots of other very strong environmental drivers.
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No one knows why, but salt does appear to affect endothelial function (lining of blood vessels), which might be part of the reason.
Prolonged exposure to high plasma sodium concentrations i.e. >140mM induces a fluid shift from the interstitial to intravascular space by facilitating deterioration of the negatively-charged heparan sulphate moiety of the endothelial glycocalyx - thus upregulating Na entry into endothelial sodium channels.
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Prolonged exposure to high plasma sodium concentrations i.e. >140mM induces a fluid shift from the interstitial to intravascular space by facilitating deterioration of the negatively-charged heparan sulphate moiety of the endothelial glycocalyx - thus upregulating Na entry into endothelial sodium channels.
Pflugers Arch. 2011 Oct;462(4):519-28. doi: 10.1007/s00424-011-0999-1. Epub 2011 Jul 28.
Salt overload damages the glycocalyx sodium barrier of vascular endothelium.