Two studies reported in The New England Journal of Medicine have shown that too little salt in the diet is linked to cardiovascular problems. The studies were part of the Prospective Urban Rural Epidemiology research project. A total of 100,000 adults from 18 different countries participated in the study and were followed for just less than four years.
The relationship between both sodium and potassium on blood pressure levels, as well as cardiovascular events and deaths, was analyzed. The first publication reported the relation between sodium excreted in urine and blood pressure. The results showed that blood pressure increased with each gram of sodium excreted per day, however, the association was most pronounced at five grams of sodium or more. The sodium effect on blood pressure was more evident in those with hypertension compared to those without hypertension, and was also more evident in older people. An inverse pattern was found with potassium.
In the second publication, cardiovascular outcomes were reported. The results showed that people who had seven or more grams of sodium excreted per day had a 15% increase in risk for cardiovascular events or death. This outcome was especially significant for people with hypertension. The interesting outcome of this study, that many would consider controversial, is that people with the lowest levels of sodium excretion; that is, below three grams per day, had a 27% increase in the risk for cardiovascular events. The group with the lowest sodium excretion levels had a high level of risk for cardiovascular events, but it was not linked to high blood pressure. In this second study, they also found an inverse pattern for potassium.
An interpretation of the findings is that both high and low levels of sodium seem to be associated with risk for cardiovascular events. Average levels of salt intake seem to be optimum. Whereas guidelines about salt intake have been to keep levels low, these new studies are suggesting that there is such a thing as too little salt in the diet. The old saying, “everything in moderation,” may be the message here.
Two other articles that are related were also published in the same issue of The New England Journal of Medicine. One article reported results from a very large study based on the 2010 Global Burden of Diseases Nutrition and Chronic Diseases Expert group data. The results from this study suggested that high salt levels were attributed to 1.65 million deaths due to cardiovascular events. As an attempt to reconcile, or at least to compare, the results from this study linking high salt levels to cardiovascular risks and the two studies that linked both high and low salt levels to cardiovascular risks, an editorial article was published in the same issue of the journal by Suzanne Oparil, who is an expert on high blood pressure and is a Professor of Medicine at the University of Alabama in Birmingham.
The debate about too little or too much salt as a risk factor for cardiovascular problems will likely escalate as a result of the publication of these studies. Recognition of the complexity of salt, potassium, other dietary habits and exercise as factors that play a role in the development of cardiovascular problems will likely be at the forefront of the debate.
By Margaret Lutze
(See GLV article “Too Much Salt Linked to Cardiovascular Deaths, According to Study”)