Nothing gets people stirred up like a food fight. Emotions run strong when it comes to the things we love to hate, such as salt.
For decades Americans have been told to shun the salt shaker. The message has been that sodium causes the body to retain fluid which in turn raises blood pressure which leads to atherosclerosis which causes heart attacks and death. Cut back on sodium and you reverse the process: blood pressure comes down, which leads to less atherosclerosis, fewer heart attacks and longer life.
That has been the collected wisdom for a very long time. Trouble is, the data have not always matched up with the theory. A meta-analysis of 167 studies (published online in the American Journal of Hypertension, January, 2012) revealed that reducing sodium in the diet had a modest impact on blood pressure. That seems reasonable, though the effect was nothing to write home about. People with normal blood pressure saw a 1% reduction in blood pressure readings on a low-salt regimen. Those with hypertension achieved a 3.5% reduction.
What was unanticipated was that there were negative effects of the low-salt approach. Salt restriction led to higher levels of cholesterol (2.5% increase) and triglycerides (7% increase). In addition, there were increases in stress hormones including adrenaline (epinephrine) renin and aldosterone. There is growing evidence that higher levels of renin have negative effects on the cardiovascular system and may lead to an increased risk of heart disease, heart attacks and death. So, although cutting back on salt led to a modest reduction in blood pressure, this benefit was offset by increases in cholesterol, triglycerides, renin, aldosterone and epinephrine.
Renin is a hormone made by the kidneys. It is one of the ways the body controls blood pressure. When the kidneys sense that there is less sodium in the body, renin levels increase and lead to a cascade of other biochemical changes. They are designed to preserve sodium and water and raise blood pressure. In other words, the body is exquisitely tuned to detect lowered levels of sodium and respond in an adaptive manner to preserve this electrolyte.
Another study, published in the Journal of the American Medical Association (May 4, 2011), added fuel to this fire. Most studies of diet and disease have had to rely on peoples’ faulty memories about what they eat. Not infrequently, people may not be as honest or accurate in their recall what they ate. The JAMA study was fascinating because the investigators actually measured sodium excretion. In other words, they measured the amount of sodium in the urine of their 3,500 subjects. This is a highly accurate method for determining how much salt these people actually consumed. That’s because the body is very good at eliminating sodium and this directly correlates with how much is swallowed.
The unexpected findings of this eight-year study were: the people with the lowest salt intake had the highest mortality stats. Those with the highest sodium intake were the least likely to die from cardiovascular complications.
The bottom line: The salt controversy remains as confusing and controversial as ever. If you would like to listen to our interview with the lead investigator of the salt study, check our recent podcast on “Dealing with Medical Flip Flops.” The researcher who talks about the salt study is the last interview on the one-hour show…about 45 minutes in.
Not everyone who listened to the data that were presented liked what they heard. Alex C. was quite indignant:
“The discussion about the recent publication in JAMA regarding sodium intake was superficial at best. The hosts gave too much credence to this study and failed to point out that the CDC and a number of extremely qualified researchers have directly questioned its results.
“Simply acknowledging that people disagree with the findings of this study does not cut it; explain why there are disagreements with the study if you are going to highlight it as a major scientific finding. Having the author of the article acknowledge a few of the lesser short-comings of the study design is insufficient.
“The flippant acceptance of this single study by the People’s Pharmacy is especially notable given that the entire episode’s central theme was about medical flip-flopping with a caveat that no single study should guide public health decisions.
“The NY Times covered the controversy of this study well, and as responsible journalists, The People’s Pharmacy would be wise to follow their lead on the issue of dietary sodium before claiming that this JAMA study may demonstrate that dietary salt is beneficial.”
No one ever said salt was beneficial. The results of the study demonstrated that low sodium excretion (the best determinant of salt intake) is associated with a higher risk of cardiovascular mortality. This is not the first time such an association has been uncovered.
Speaking of the New York Times. You may wish to read this op-ed piece just recently published: “Salt, We Misjudged You.”
The Cochrane Collaboration represents the highest level of scientific scrutiny of studies. Last year the this independent and objective organization published the following conclusion:
“we do not know if low salt diets improve or worsen health outcomes.”
So, what are we do make of this controversy? If one accepts the wisdom of the Cochrane Collaboration and its very careful analysis of all the collected data over many decades, there is no firm conclusion that salt restriction improves health outcomes. We have a hard time accepting this uncertainty in large measure because organizations we trust like the CDC, the FDA and the NIH assert that cutting back on salt will be good for us and won’t harm us.
When something is repeated often enough it becomes an article of faith. We were told by organizations we trust that eggs were bad for us and would raise our cholesterol levels and give us heart attacks. The data eventually proved otherwise. We were told that calcium helps build bones and that people over 51 years of age should be getting 1200 mg of calcium daily. That often means calcium supplements. But new data suggests that article of faith is wrong and that calcium supplements might actually increase the risk of heart attacks. Eventually the data trump belief, but it can take a long time. We would never suggest that salt is good for you…but the data do not demonstrate that salt restriction saves lives.
We know this is a challenging and perhaps even heretical message. We hope you will read some of the articles we have highlighted above (links to the original articles, especially the Cochrane Collaboration, will provide you access to the collected wisdom on this topic).
We welcome your comments about the salt controversy below.
