Why salt is bad.
Firstly, there are 6 distinct levels of salt consumption- see bottom of this
post. This is what really stuffs things up. The other thing that stuffs it
up is the need to measure slat excretion, rather than intake.
Loren Cordain also publiushed a small study showing a significant effect on
exercie induced asthma. The Cochrane reivew fails to mention time period-
I'll bet most studies are 8-16 week. That's of no practical value- it's what
happens over the long long term that matters especially with hypertension.
Why do people love the taste of salt (or sodium anyway)?- My opinion:
Blood and extracellular fluid are high in sodium 140mmol/l, whereas cells
have low sodium (5mmol/l). These days we blees our meat before eating it.
CfF in the wild, the slaughtttered animal is eaten immediately- blood and
all and therefore tasdstes very salty. Simple. (I haven't asked my salt
expert friend about this).
Am J Hypertens 1997 May;10(5 Pt 2):37S-41S
Salt--more adverse effects.
MacGregor GA
Department of Medicine, St. George's Hospital Medical School, London,
England.
Salt intake has been shown to be the most important determinant of blood
pressure differences both between populations and within populations, as
well as the main determinant of the rise in blood pressure with increasing
age. In spite of this overwhelming evidence, the food industry for
commercial reasons has sustained an artificial debate about the importance
of salt intake. This has distracted attention from the other serious effects
that a high salt intake may have. A high salt intake (a) exacerbates
conditions where there is already sodium and water retention; (b) is the
rate limiting factor for carcinoma of the stomach; (c) contributes to left
ventricular hypertrophy; (d) is likely to hasten deterioration of renal
function and renal disease; (e) is an exacerbating factor in asthma; and (f)
increasingly is suggested as a major aggravating factor in osteoporosis.
Lancet 1997 Sep 27;350(9082):957
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>From the Cochrane Library (the Mecca for evidence based medicine)
Effect of reduced dietary sodium on blood pressure: a meta-analysis of
randomized controlled trials.
Midgley J P, Matthew A G, Greenwood C M, Logan A G. 1996. Effect of reduced
dietary sodium on blood pressure: a meta-analysis of randomized controlled
trials. Journal of the American Medical Association 275(20): pp.1590-1597.
The dietary intervention effect averaged 95 mmol/d (71-119 mmol/d) in the 28
hypertensive trials and 125 mmol/d (95-156 mmol/d) in the 28 normotensive
trials. There was significant heterogeneity among trials in the effect of
dietary sodium restriction on blood pressure. Accounting for study design
and quality did not eliminate the heterogeneity.
After adjustment for measurement of error of urinary sodium excretion of
urinary sodium excretion, regression analysis showed a decrease in blood
pressure for a 100 mmol/d reduction in daily sodium excretion of 3.7 mmHg
(2.35-5.05 mmHg) for systolic (p <0.001) and 0.9 mmHg (-0.13 to 1.85 mmHg)
for diastolic (p=0.09) in the hypertensive trials. For the same reduction in
daily sodium excretion, the normotensive trials showed decreases of 1.0 mmHg
(0.51-1.56 mmHg) in systolic blood pressure (p <0.001) and 0.1 mmHg (-0.32
to 0.51 mmHg) for diastolic blood pressure (p=0.64).
A statistically significant intercept, representing a decrease in blood
pressure with no change in dietary sodium intake, was observed in the
hypertensive trials for both systolic and diastolic blood pressure.
Subgroup analysis demonstrated large decreases in blood pressure in the
trials of older hypertensive individuals. In the 14 trials of normotensive
non-institutionalised subjects whose meals were prepared for them there was
no evidence of a significant change in blood pressure.
Publication bias was examined and found to be evident in favour of small
trials reporting a reduction in blood pressure.
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HERE"S what I posted before (cut from another list- Australia's leading salt
expert): (sorry it wasn't Yanomano Indians, it was Yanomama)(the lawn bit
refers to a comment I made about people fainting on low salt diets- which
normally is confined to people taking diuretics(these work by causing
increased salt excretion0 who then go on a low salt diet- a bad
combination).
If you want the fittest person on earth to mow your lawn, look no further
than the Yanomama Indians of the remote rainforest of Brazil and Venezuela.
They are the world's most salt free society with an estimated intake of 6
mmol/day and a 24-hour sodium excretion rate of less than 1 mmol (one
millimole). Most of the 6 mmol is lost in faeces, sweat and lactation,
leaving virtually none for the urine. Note that in industrial societies
the 24-hour urinary excretion represents about 90% of intake, so for
practical purposes, such as setting the RDI for sodium, the RDI of 40-100
mmol/day refers to the intake as estimated by excretion rate. When you
talk about intakes you measure them by excretion rates, and you don't
bother to correct for the 10% difference.
You couldn't find a better advertisement for the Paleodiet than the
Yanomama (syn. Yanomamo, Yanomamö), except that admittedly they live in
settlements and grow vegetables to supplement the meat, fruit and
vegetables obtained by hunting and gathering. Their robust health, superb
fitness and stamina are legendary (see the book 'Yanomamö, the Fierce
People', by anthropologist N A Chagnon, who spent 12 years with them).
Some people assume that a love of salt is natural 'because animals love it
too', but Chagnon records that the Yanomama detest salt when they first
taste it (they don't go for salt licks like the herbivores that develop
sodium deficiency on virtually salt free pasture). There are about 20
salt free societies and not one of them has ever been offered salt as a
public health measure (note the contrast between regional availability of
sodium and iodine as natural components of the diet).
The learning curve of GPs about salt doesn't move until they begin to
measure intake by 24-hour excretion. Before that neither the patient nor
the GP have the faintest idea how much salt is being eaten-the blind are
leading the blind. Some people who have sworn that they neither cooked
with salt nor added it at the table, and have avoided salty foods
religiously and kept no salt in the house, have actually passed over 200
mmol of sodium in a 24 hour urine collection.
Stepwise taste perception of salt requires logarithmic increases in
concentration, and most people assume that the pathophysiological effects
also require log changes, in line with most drugs, where effective dose
changes commonly involve doubling or halving. It is useful to distinguish
six levels of intake, starting with the Yanomama at 6 mmol/day and
multiplying by 2.5. Rounding some of the figures this gives the series:
Level 1 6-15 mmol/day
Level 2 16-40 mmol/day
Level 3 40-100 mmol/day
Level 4 100-250 mmol/day
Level 5 250-650 mmol/day
Level 6 650-1600 mmol/day
Level 1 (using the Kempner diet) is the only non-pharmacological treatment
known to reverse some cases of malignant hypertension. Instead of the
Kempner diet, a more palatable alternative is to take up anthropology, live
with the Yanomama and eat their Paleodiet.
Level 2 is the Paleodiet with more meat and fish than the Yanomama are able
to catch.
Level 3 is the RDI for sodium, intended for the whole population of
Australia
Level 4 is eaten by hapless victims of the status quo. I know salt is hard
to avoid, but so is fat. Does that mean we must do nothing? Yes, let's
ignore fat, because we can't even measure the 24-hour intake.
Level 5 is what a patient of mine excreted in the 24 hours after living
away from home on take-away food for a whole weekend (he excreted 578 mmol,
in a collection with normal volume, potassium and creatinine content).
Level 6 is an experimental diet that raised the BP of all volunteers (n=14)
within 3 days.
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