National policies that advise restricting sodium (salt) intake to reduce the risk of hypertension might not provide the anticipated cardiovascular benefits and may even be detrimental to health, report researchers in an article in today’s JAMA.
In the study, the researchers categorized the 3681 study participants according to sodium intake, using a procedure that measures sodium in the urine over a 24-hour period, considered the gold standard for such assessment. At a median of nearly 8 years later, participants in the group with the lowest sodium intake at the beginning of the trial were significantly more likely than the other 2 groups to die of cardiovascular disease.
The researchers also found that these 3 groups had the same risk of developing hypertension, regardless of initial sodium intake. They did find in a subgroup of 1499 study participants who had sodium intake measured at the beginning and at the end of the study that an increase in sodium intake was associated with an increase in systolic (but not diastolic) blood pressure. However, this relationship did not result in a higher risk of complications from hypertension or cardiovascular disease, such as heart attack or stroke.
Jan A. Staessen, MD, PhD, professor of medicine at the University of Leuven in Belgium and one of the study’s authors, discusses his team’s findings:
news@JAMA: Are you surprised by your results?
Dr Staessen: Not so much. We started this research more than 25 years ago, and in all our studies, it was almost impossible to find an association between blood pressure and 24-hour sodium excretion. We were a bit surprised to see an inverse relationship between sodium intake and cardiovascular death.
news@JAMA: Why would lowering sodium intake possibly increase cardiovascular risk?
Dr Staessen: Ours is an epidemiological study so we cannot be sure of the underlying mechanism. But if you decrease sodium intake a lot, you activate some of the systems that conserve sodium and they are known to have a negative influence on cardiovascular outcomes. This may be an underlying mechanism.
news@JAMA: Where does your study fit into the discussion of mandating sodium restriction in foods to improve health, as advocated by some public health officials and government agencies?
Dr Staessen: One should be very careful when one wants to implement [sodium restriction], as it is based on short-term studies mainly in hypertensive populations. Whether one can extrapolate these short-term results over the long term remains to be seen, especially as our study and 2 previous studies have shown an inverse association between sodium intake and mortality.
news@JAMA: What is needed to provide a clearer picture of the benefits and risks of controlling sodium consumption?
Dr Staessen: What one needs is a long-term interventional study to look at cardiovascular complications. Reducing blood pressure is not what one is in this for. You want to show that it actually changes cardiovascular outcomes.