September 15, 2014

The anti-salt craze is dying

I have been banging on for some years about the idiocy concerning table salt that pervades public health warnings.  Governments are always leaning on food processors to reduce the salt in their products.  That less salty foods are not as safe from bacterial contamination seems to be ignored.

The genesis of the warnings is partly theoretical and only weakly empirical.  The factual part is that high salt intake is correlated with both increased blood pressure and more frequent cardiovascular disease.  But correlation is not causation so the proof is weak.

The first big crack in the dam was a 2011 report in JAMA of a high quality study of the matter.  Its conclusion: "In this population-based cohort, systolic blood pressure, but not diastolic pressure, changes over time aligned with change in sodium excretion, but this association did not translate into a higher risk of hypertension or CVD complications. Lower sodium excretion was associated with higher CVD mortality."

So it was LOW salt levels that killed you!

That study was greeted with a fair amount of outrage and accusations that it was just an unrepeatable "one off" result.

The dominoes are now falling, however.  Just this year another good study exonerating salt has come out.  Abstract below:

Relationship Between Nutrition and Blood Pressure: A Cross-Sectional Analysis from the NutriNet-Santé Study, a French Web-based Cohort Study

Helene Lelong et al

Abstract

BACKGROUND Hypertension is the most prevalent chronic disease worldwide. Lifestyle behaviors for its prevention and control are recommended within worldwide guidelines. Nevertheless, their combined relationship with blood pressure (BP) level, particularly in the general population, would need more investigations. Our aim in this study was to evaluate the relative impact of lifestyle and nutritional factors on BP level.

METHODS Cross-sectional analyses were performed using data from 8,670 volunteers from the NutriNet-Santé Study, an ongoing French web-based cohort study. Dietary intakes were assessed using three 24-hour records. Information on lifestyle factors was collected using questionnaires and 3 BP measurements following a standardized protocol. Age-adjusted associations and then multivariate associations between systolic BP (SBP) and lifestyle behaviors were estimated using multiple linear regressions.

RESULTS SBP was higher in participants with elevated body mass indices (BMIs). Salt intake was positively associated with SBP in men but not in women. The negative relationship between consumption of fruits and vegetables and SBP was significant in both sexes. Alcohol intake was positively associated with SBP in both sexes; physical activity was not. The 5 parameters representing the well-accepted modifiable factors for hypertension reduction plus age and education level, accounted for 19.7% of the SBP variance in women and 12.8% in men. Considering their squared partial correlation coefficient, age and BMI were the most important parameters relating to SBP level. Salt intake was not associated with SBP in either sex after multiple adjustments.

CONCLUSIONS BMI was the main contributory modifiable factor of BP level after multiple adjustments.

Am J Hypertens (2014)

So it was being overweight that killed you, not salt.

So how come people have been getting it wrong?  A theoretical article recently tidies up the loose ends.  There is no abstract associated with it so I reprint the first part of it -- showing that  it was a case of the causal arrow pointing the wrong way:

An Unsavory Truth: Sugar, More than Salt, Predisposes to Hypertension and Chronic Disease

James J. DiNicolantonio et al.

He et al state that the association between sugar-sweetened beverage consumption and blood pressure may be mediated, at least in part, by salt intake. We take the issue with several points made by the authors and make a case for quite different conclusions. The authors state that "salt is a major drive to thirst": "an increase in salt intake will increase the amount of fluid consumed, and if part of this fluid is in the form of soft drinks, sugar will be increased proportionately." In other words, salt consumption drives fluid intake, and sugar may just, coincidentally, come along for the ride. We would argue something more akin to the opposite. Sugar consumption leads to insulin spikes, low blood sugar, and hunger. Sugar is a major drive to hunger: an increase in sugar will increase the amount of food consumed, and if part of this food is in the form of processed foods, sodium will be increased proportionately. In other words, sugar consumption drives food intake, and sodium may just. coincidentally, come along for the ride. Processed foods are the principal source of dietary sodium. They also happen to be predominant sources of added sugars.

American Journal of Cardiology, Vol. 114, Issue 7, p1126–1128

For other findings that alerted me to the salt nonsense, see the sidebar of my  FOOD & HEALTH SKEPTIC blog





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