Friday, November 25, 2011


A long time ago, sometime in 2009, I wrote about the desired salt intake to prevent hypertension and stroke. At that time, the body of evidence seemed to be that taking less salt is good for us. The data was mainly driven by the British school of thought and my friend Dr Graham McGregor in UK. Since then, much work has been done, with some studies finding no correlation between salt intake and CV events, and some showing that too little salt intake is associated with increase CV events.
Well, Dr Martin O'Donnell of McMaster U, Hamiltoon, and colleague has published a paper in the 23rd Nov issue of the Journal of the American Medical Association, addressing this issue and adding more fire to the controversy.
They took a look into two large hypertension trials done earlier, the On-Target Trial and the Transcend trial, a total of 29,000 patients, on 56 months of follow-up. They looked into the Urinary Sodium excretion as a marker of sodium intake, meaning the higher the sodium intake the higher the Urinary Sodium, and vice versa. This has been established. They then correlated the Urinary sodium excretion levels with CV events. They found increase CV evenets in those with too high Urinary sodium ( >7gms/day ), and too low Urinary Sodium ( < 3 gms / day ).

<2 g/d
2-2.99 g/d
6-6.99 g/d
7-8 g/d
>8 g/d
All CV events
1.21 (1.03-1.43)
1.16 (1.04-1.28)
1.09 (0.99-1.20)
1.15 (1.00-1.32)
1.49 (1.28-1.75
CV death
1.37 (1.09-1.73)
1.19 (1.02-1.39)
1.11 (0.96-1.29)
1.53 (1.26-1.86)
1.66 (1.31-2.10)
1.06 (0.76-1.46)
1.05 (0.86-1.28)
0.95 (0.79-1.15)
1.06 (0.81-1.40)
1.48 (1.09-2.01)

This now lends us in more confusion. If their data is correct, one of the ways is to say that that is a J-curve in CV events with sodium intake. Neither too high, nor too low is good.
Obviously there are difficulties with this paper. The data was largely observational from trials not meant to study this. The long part of the J-curve, most of us will easily agree, as it can be easily demonstrated. The low sodium intake end ( short end of the J-curve) is more difficult to explain. Were these patients too sick, to take in salt? Did they have more complications from their hypertension, causing them not to be able to take in food / salt?
Anyway, in science, sometimes it is good to be controversial. It makes us think, and not swallow everything hook line and sinker.
How much salt then should I take? Well, if you believe them McMaster boys, then, not more then 7gms / day, and not less then 3 gms/day. Know that for every gram of salt you take in, you also pass out in the urine, the equivalent amount ( generally speaking, 7 gms sodium/day ingestion will give rise to 7gms sodium/day, urinary excretion ).
I suppose if you look at it philosophically, in life, everything must be in moderation. Extremes are bad for us.

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