The lurking danger of salt restriction

saltOverall, medical students receive less than 20 contact hours of nutrition instruction during their medical school careers. It partially explains why bad dietary advice from doctors is so common. In my previous previous article you can read that many foods that are generally considered to be healthy, are actually significant contributors to diabetes and chronic disease. Because most doctors don’t keep up with the scientific literature on nutrition, they are not shy in recommending these harmful foods, especially to people who are most vulnerable to it. Surprisingly, doctors are pretty careful when it comes to controlling our intake of salt. It has to be restricted because, after all, we all consume way too much of it and we all know it causes hypertension and heart disease. The question is: how much salt can we safely consume? What does science say? The answers may surprise you.

Evidence is often inconsistent

Recently, the Institute of Medicine (IOM) was commissioned by the Centers for Disease Control and Prevention of the U.S. Department of Health and Human Services (HHS) to review all the studies relating to the health effects of sodium intake. Their report, ‘Sodium intake in populations’, was released last year and concluded that the quality of the current evidence linking salt to health outcomes is poor. The committee considered doing a meta-analysis to assess the evidence, but couldn’t because of ‘the marked heterogeneity among the reviewed studies, particularly with respect to variations in measuring sodium intake and adjusting for cofounders.’ Because of this, each study had to be assessed on an individual basis. The committee found that ‘all of the evidence on the health outcomes related to CVD, stroke and mortality was observational’. This is important because observational studies ‘cannot provide definitive evidence of safety, efficacy, or effectiveness’ but can ‘help formulate hypotheses to be tested in subsequent experiments‘. In other words: observational studies help us to develop theories, but don’t provide us with strong evidence.

However, evidence on health outcomes related to heart failure, did include some randomized clinical trials (RCTs), which are considered the gold standard for a clinical trial. The committee concluded that the evidence indicates a positive relationship between higher levels of sodium intake and risk of Cardio Vascular Disease (CVD). The daily salt intake however, above which the risk of cardiovascular disease increases, remained unclear. The report concludes that ‘the evidence is inconsistent and insufficient to conclude that lowering sodium intakes below 2,300 mg per day’ (the current advised maximum) ‘either increases or decreases risk of CVD outcomes.’ Basically, that is as conclusive as saying that drinking too little or too much water can kill you.

Average daily salt intake in Western World no reason for concern

In january 2014, an article was published in the American Journal of Hypertension, revealing the results of a meta-analysis of 25 studies, including 274,683 individuals, investigating the incidence of all-cause mortality and cardiovascular disease events in populations exposed to dietary intakes of low sodium (<115 mmol), usual sodium (low usual sodium: 115–165 mmol; high usual sodium: 166–215 mmol), and high sodium (>215 mmol). The meta-analysis concluded that an intake of 2,645 — 4,945 mg of sodium per day (most Americans fall within this range) results in more favorable health outcomes than the current recommendations by the U.S. Centers for Disease Control and Prevention and major health departments. They recommend a maximum intake of 2,300mg/ day for healthy individuals under 50 years old, and less than 1,500 mg/day for most over 50 years old. Although the study found that both excessively low or high salt intake were associated with decreased survival, little-to-no variation in health outcomes was found between individuals as long as their consumption remained within the ideal intake range (2,645 — 4,945 mg/day). So, a low sodium diet doesn’t seem to decrease all-cause mortality or cardiovascular disease and even involves a health risk.

Recommended salt intake probably too low

Conclusions of the Prospective Urban Rural (PURE) study, published on the 13th of August 2014 in the New England Journal of Medicine, confirm the findings of the previously mentioned article in the American Journal of Hypertension. The PURE study is the largest of its kind and followed more than 100.000 people for nearly 4 years and assessed sodium and potassium intake and related them to blood pressure as well as to deaths, heart disease and strokes. The lowest risk of death and cardiovascular events was seen among participants with an estimated sodium excretion between 3,000 mg  and 6,000 mg per day. The average American consumes about 3500 mg of salt per day, which is well within the healthy range. In fact, a large research performed in the eighties among 52 population groups around the world, showed no clear pattern between the level of salt intake and blood pressure. The PURE study concludes however, that blood pressure can significantly increase in people who already have a high blood pressure or are older than 55 years, when they consume more than 5,000 mg of sodium per day, which is really quite high.

So, the evidence doesn’t support the recommendation of a low salt diet for the vast majority of people. In fact, low sodium intake involves health risks, including elevations of hormones that increase chances or death and cardiovascular disease. Interestingly, people consuming higher levels of potassium rich foods show a reduction in cardiovascular mortality, possibly through a positive effects on blood pressure. In previous research, potassium rich foods have been demonstrated to counter the pathophysiological effects of consuming excess salt, including salt-sensitivity, which is a likely precursor of hypertension. Eating lots of different vegetables, including potassium rich ones, may very well be a more effective method to lower blood pressure than lowering salt intake.

Categories: Food, Health, Other

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