May 12, 2006

Ms. Mary Bush
Director General
Office of Nutrition Policy and Promotion
Health Canada
2936 Baseline
Nepean, ON   K1A 0K9
Canada 

Dear Ms. Bush: 

My apologies for our tardiness in participating in your review of Canada’s Food Guide to Healthy Eating.  Your consultation was extensive, but until the stakeholders meeting last month, it had escaped our attention that you intend to alter the recommendation regarding dietary salt to encourage Canadians to “avoid adding salt to the foods you prepare and eat.  Use Food Labels to choose products lower in sodium.” 

As you are doubtless aware, in 1999, the Canadian Hypertension Society, the Canadian Coalition for High Blood Pressure Prevention and Control, the Health Canada Laboratory Centre for Disease Control and the Heart and Stroke Foundation of Canada issued a joint statement opposing general recommendations for sodium reduction.[1]  These organizations specifically recommended against general restriction of salt intake in the normotensive population.  We understand your charge to be that “The Food Guide will promote a pattern of eating that will meet nutrient needs, promote health and minimize the risk of nutrition-related chronic disease” and are dismayed that Health Canada would embrace the flawed IOM DRI report in preference to Canada’s own experts. 

Your charge is to ensure that “revisions to the Food Guide will be based on the most up-to-date evidence,” so we would ask what evidence could be offered that restricting salt would “promote health and minimize the risk of nutrition-related chronic disease.”  We all well recognize that salt is related to blood pressure, a heterogeneous relationship that suggests an overall blood pressure reduction in a population of several millimeters (systolic) for a two-thirds reduction in dietary sodium – ignoring the equally well-demonstrated fact that a substantial minority of the population will, in fact, record increased blood pressure on such a salt-restricted diet.  Even if every single Canadian were to achieve the posited blood pressure lowering through salt restriction, however, such an achievement would not necessarily improve “health” or “minimize the risk of nutrition-related chronic disease.”  Elevated blood pressure is an important risk factor for cardiovascular events, but is not, in itself, a “chronic disease.”  It is symptomatic of several chronic diseases (atherosclerosis, diabetes, etc.) and eminently worthy of public health concern, but the reality is a good deal more complicated.  We would commend your original charge that your recommendations be focused on minimizing the risk of chronic disease.  Within the range of intakes of most Canadians, salt is not responsible for adverse health outcomes. 

Salt is essential not only to life, but to good health.  Salt maintains the electrolyte balance inside and outside of cells.  Salt is not only the key to proper hydration, but the essential carrier used to prevent Iodine Deficiency Disorders and cystic fibrosis is most likely caused by a deformed protein that prevents chloride outside cells from attracting needed moisture.  Chronic Fatigue Syndrome has been treated with great success using high salt diets.  Salt is also relied upon as the carrier for fluoride and iron and is being used to deliver medication in tropic countries for the prevention of lymphatic filarisis.  In Eastern Europe, asthmatics and others suffering respiratory illness are treated by interring them in salt mines.  Great care is required not to stigmatize salt without consistent and high quality evidence.  

The argument is made by some, including the IOM/DRI report, that salt’s blood pressure impact on cardiovascular risk warrants salt restriction.  Let’s examine that evidence.  Blood pressure is a sign.[2]  When it goes up (or down) it indicates an underlying health concern.    Changes result from many variables, often still poorly-understood.  High blood pressure is treated with pharmaceuticals and with lifestyle interventions such as diet and exercise.  Health Canada approves anti-hypertensive drugs; to be approved, these drugs must prove they work to lower blood pressure.  Whether they also work to lower the incidence of heart attacks and strokes has not been the test to gain approval (it would take too long to develop new drugs), but the U.S. National Heart, Lung and Blood Institute has invested heavily in such “health outcomes” studies.   It is these “health outcomes” that are the “risk of chronic disease” the prevention of which is Health Canada’s stated objective.

What do the “health outcomes” studies of salt restriction show?  We need note first that there has never been a controlled trial of the health outcomes of salt restriction.  So, basically, we don’t know what the outcomes are.  A controlled trial is badly needed.  Some would argue that the risk of cardiovascular events is so pressing that we must act now, even in the absence of evidence showing a beneficial health outcome.  If we could ensure there are no negative side effects and if there is a pattern in the observational literature supporting the hypothesis that reducing salt will extend life or reduce the incidence of myocardial infarction and strokes, then policy-makers might risk a major population intervention.  In the presence of known confounders (negative side effects) and in the absence of observational studies showing a population benefit for a recommended intervention, in those cases where evidence from a controlled trial is lacking, it is an affront to “evidence-based medicine” to pursue the population intervention. That is the case with salt and cardiovascular risk.

As background for a review of the non-pharmacologic intervention of salt restriction to reduce the incidence of cardiovascular events, let’s look at the case of controlled trials examining the health impacts of pharmacologic interventions.  The ALLHAT study,[3] funded by the National Heart, Lung and Blood Institute (NHLBI), examined the health outcomes of four classes of anti-hypertensive drugs, all of which had demonstrated their ability to reduce blood pressure in relative safety.  Dr. Jeffrey R. Cutler of the National Heart, Lung and Blood Institute (NHLBI) supervised the study and explained its importance:  "Trials are based on the notion that different antihypertensive regimes, despite similar efficacy in lowering blood pressure, have other beneficial or harmful effects that modify their net effect on cardiovascular or all-cause morbidity and mortality."[4]

Lifestyle interventions are "antihypertensive regimes" too.    For years, the same situation prompting the ALLHAT trial applied to lifestyle interventions designed to improve blood pressure -- they were untested regarding health outcomes.  Certain dietary and lifestyle interventions reduced blood pressure, at least in sensitive sub-populations.  Whether they also reduced the incidence of heart attacks and strokes had never been tested.  Thus, until fairly recently, scientists had never tested the health results of the “salt hypothesis.” Even today, we have only observational studies relating salt intake with health outcomes.  We have no controlled trial which we should prefer before making population advisories. 

Even documenting an association of, for example, low-sodium diets with reduced incidence of heart attacks in an observational study, would only be the first step.  Association is not the same as causation, of course, but strong and consistent observational results, as mentioned above, might be offered as plausible support for an intervention (hopefully, while the hypothesis is tested with a controlled intervention.

Unfortunately for advocates of universal salt restriction, the totality of the observational studies rejects the salt hypothesis.  There have been only 13 studies reported, eleven of them in populations with salt intake ranges similar to the Canadian population.  In those studies, not a single one identified a reduction of cardiovascular risk or improved mortality among those considered “low sodium.”  On the other hand, four of the studies found statistically significant additional risk in the low-salt groups.  The most recent study,[5] a follow-up analysis of the U.S. government’s National Health and Nutrition Examination Survey (NHANES II) found that following the IOM/DRI recommendation was associated with 37% higher mortality.

The earlier twelve studies included:

1.         A ten-year study of nearly 8,000 Hawaiian Japanese men concluded:  "No relation was found between salt intake and the incidence of stroke."[6]

2.         An eight-year study of a New York City hypertensive population stratified for sodium intake levels found those on low-salt diets had more than four times as many heart attacks as those on normal-sodium diets – the exact opposite of what the “salt hypothesis” would have predicted.[7]

3.         An analysis by NHLBI’s Dr. Cutler of the first six years’ data from the MRFIT database documented no health outcomes benefits of lower-sodium diets.[8]

4.        A ten-year follow-up study to the huge Scottish Heart Health Study found no improved health outcomes for those on low-salt diets.[9]

5.        An analysis of the health outcomes over twenty years from those in the massive US National Health and Nutrition Examination Survey (NHANES I) documented a 20% greater incidence of heart attacks among those on low-salt diets compared to normal-salt diets.[10]

6.        A health outcomes study in Finland, reported to the American Heart Association that no health benefits could be identified and concluded “…our results do not support the recommendations for entire populations to reduce dietary sodium intake to prevent coronary heart disease.”[11]

7.        A further analysis of the MRFIT database, this time using fourteen years’ data, confirmed no improved health benefit from low-sodium diets.    Its author conceded that there is "no relationship observed between dietary sodium and mortality."[12]

8.          A study of Americans found that less sodium-dense diets did reduce the cardiovascular mortality of one population sub-set, overweight men – the article reporting the findings did not explain why this obese group actually consumed less sodium than normal-weight individuals in the study.[13]

9.        A Finnish study reported an increase in cardiovascular events for obese men (but not women or normal-weight individuals of either gender) – the article, however, failed to adjust for potassium intake levels which many researchers consider a key associated variable.[14]

10.       In September, 2002, the prestigious Cochrane Collaboration produced the latest and highest-quality meta-analysis of clinical trials.  It was published in the British Medical Journal and confirmed earlier meta-analyses' conclusions that significant salt reduction would lead to very small blood pressure changes in sensitive populations and no health benefits.[15]

11.       In June 2003, Dutch researchers using a massive database in Rotterdam, concluded that "variations in dietary sodium and potassium within the range commonly observed in Westernized societies have no material effect on the occurrence of cardiovascular events and mortality at old age."[16]

12.       In July 2004, researchers found that in a Japanese population, "low" sodium intakes (about 20% above Americans' average intake) had one-third the incidence of fatal strokes of those consuming twice as much sodium as Americans.[17]

We read this universe of salt restriction health outcomes studies as consistent in finding absolutely no support for universal salt restriction to “promote health and minimize the risk of nutrition-related chronic disease.”   Since the observational data do not support your draft recommendation and in the absence of a controlled trial with any evidence that such a recommendation would “promote health and minimize the risk of nutrition-related chronic disease,” we respectfully request that you reconsider your draft regulation on salt.

Respectfully submitted,

Richard L. Hanneman
President

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