Are low-sodium diets unhealthy? Two studies1,2 published in the August 14th issue of The New England Journal of Medicine would have us believing that’s the case. They received significant media attention, including an article in The Wall Street Journal titled: “Low-Salt Diet Poses Health Risks, Study Finds.”
In the world of science, outliers like the above do occur. But the overwhelming majority of data have consistently affirmed the benefits of lower-sodium diets (sodium is the main component of salt) in lowering high blood pressure and the risk of cardiovascular diseases like heart attacks and strokes. The research is so strong that U.S. government agencies, the World Health Organization, the American Heart Association, and other public health groups have set daily dietary sodium targets between 1,500 and 2,300 milligrams or lower. Several announced, in response to the new research, that they have no intention of changing their guidelines.
It is important to note that the two studies had significant shortcomings. Analyzing data on 100,000-plus people ages 35 to 70 years, the authors concluded that 3.1% of those who consumed between 3,000 and 6,000 milligrams of sodium daily either died or suffered congestive heart failure, heart attacks, or strokes. Among those eating less than 3,000 milligrams of sodium daily, the percentage was 4.3%.
The first major problem with these studies was their very short length. The authors reached their conclusions based on an average of only 3.7 years, and what they found was strictly an association, not cause and effect. In a short-term study like this, low-sodium intake could have been a marker of disease and poor appetite. In other words, it wasn’t the lower-sodium intake causing the diseases; the lower-sodium intake (and lower food intake overall) could simply have been a by-product of the diseases themselves. And likely, some of those diseases, like heart failure, were in part caused by many previous decades of high sodium intake.
One urine test
Another major problem was that all of the authors’ estimations for how much sodium their subjects were consuming were based on a single morning urinary sample.
More sodium, more high blood pressure
But interestingly, and despite their limitations, these studies still observed that more sodium intake was associated with higher blood pressure. Higher blood pressure over the long term, numerous past studies have affirmed, is the single greatest cardiovascular risk factor and predictor of earlier mortality.
1.65 million deaths attributed to sodium intake above 2,000 mg daily
A third study3 in the same issue of NEJM, based on data from 107 studies, found that 1.65 million deaths worldwide from cardiovascular causes in 2010 were attributed to sodium intake above 2,000 milligrams a day. Unfortunately, this study received far less attention from the media. One likely reason is that it is telling us what we already know: higher salt intake leads to higher rates of disease. This is not a headline that sells newspapers.
But it is a headline based on solid science. “High sodium intake is known to increase blood pressure, a major risk factor for cardiovascular diseases including heart disease and stroke,” summed up lead author Dr. Dariush Mozaffarian, MD, DrPH, of Tufts University.
England’s admirable results
Another recent, well-designed study4 on the benefits of sodium reduction was also dismissed by much of the media. Looking at salt reductions in England from 2003 to 2011, it found that reducing sodium in foods accounted for most of the 40% reduction in stroke and heart attacks among the British population.
Are low-sodium diets unhealthy? No. The new studies’ claims that a low-sodium intake may be dangerous undermine public health efforts to reduce excessive salt intake to treat and prevent hypertension. This is troubling, deeply troubling, because the preponderance of credible scientific data continues to show that elevated blood pressure is the single greatest cardiovascular risk factor in most populations. To improve quantity and quality of lives, the media should be focusing on the preponderance of research, not outliers.
1 N Engl J Med, 2014; 371: 601.
2 N Engl J Med 2014; 371: 612.
3 N Engl J Med, 2014; 371: 624.
4 British Medical Journal, 2014; 4: e004549.