Salt is back on trial
In just a few short months, salt has been both exonerated and indicted in major consequences for health. A new study out today puts salt back squarely in the position of the accused. With the two competing studies out within two months, how are we to make sense of the data?
The study out today, published in the Archives of Internal Medicine, is an impressive longitudinal study looking at the relationship between mortality and salt intake. One would assume that the study controls for other contributing factors to mortality, but how well it does so is always an open question. At any rate, in the new study, men consumed an average of 4,323 milligrams of sodium a day, while women took in 2,918 milligrams, compared to the 1,500 milligrams recommended by the American Heart Association. The study involved 12,000 individuals, an impressive statistical sample, and spanned 15 years.
The group with the highest sodium-to-potassium ratio had a mortality risk about 50% higher during the study than the group with the lowest, according to the report by Elena V. Kuklina, M.D., and colleagues at the Centers for Disease Control and Prevention (CDC), Emory University, and the Harvard School of Public Health.
Compare that to a report this May in the Journal of the American Medical Association which found that while healthy men and women who ate more sodium than average weren't at higher risk of dying of heart disease or stroke. Moreover, cardiovascular mortality was 56% higher for people who ate the least sodium. The eight-year study included 3,681 European men and women age 60 or younger who did not have hypertension.
Let’s parse the details out in the dense thicket of these studies. For starters, the European study involved men and women younger than 60 who had no prior problems with hypertension. This is a very important detail. Such individuals may be genetically or constitutionally protected against rises in blood pressure due to a variety of factors, including salt intake. I can tell you right now that my 63-year-old mother piles on the salt in every meal she consumes and her blood pressure cuff always registers a serene 120/70. I can also tell you that some individuals see a 10, even a 20 point hike in their blood pressure reading after gaining just five pounds and taking in an extra pinch of salt. So that’s one thing to keep in mind.
Another is to note that the latest study addresses the sodium-to-potassium ratio, not simply the gross salt intake. Sodium may be particularly corrosive when potassium is relatively low. In balance, the two, up to a point, might work synergistically to protect an individual from negative health consequences.
Finally, the study does not explicitly state what the causes of mortality were in the high-sodium study participants, and this is a crucial point. Were the causes directly attributable to hypertension, such as aneurysms and congestive heart failure, or did they span the gamut of typical chronic diseases of middle and older age? The question is important because it is not clear from the study whether the increased mortality is directly related to salt itself, or whether food and lifestyle choices of those who eat more processed foods are to blame.
"We probably should take into account the whole diet and take a more comprehensive look," says Elena V. Kuklina, M.D., one of the researchers involved in the study. "Looking at a single micronutrient, we might just miss the whole picture."
A diet rich in fruits and vegetables is naturally low in sodium and high in potassium. In contrast, a diet of processed foods tends to be the opposite -- it contains more sodium and less potassium. In addition, it is saddled with all sorts of additional dietary grenades like trans-fats, excess sugars (yes, they often lurk in combination with excess salt), and artificial additives not meant for the original human body. In short, it may not be the salt itself, but the salt in combination with other factors associated with it, that makes a high salt diet a recipe for cardiovascular disaster.
It is important to keep in mind that there are vast segments of the world’s population who take in much less salt than the West does, and they do not have the rates of hypertension and heart disease that we do. But they also eat much less food in general and certainly much less processed food. Their version of a “food desert” is not a strip of fast food joints.
In 2010, the Institute of Medicine recommended that the Food and Drug Administration regulate sodium in food. And the National Salt Reduction Initiative is a partnership of organizations -- including major food companies -- that aims to cut sodium in processed foods by 25% by 2014.