by Carole Jackson, Bottom Line Health
Itâs a mantra that weâve heard for yearsâcut back on salt! But a new study dashes that advice, demonstrating that itâs not just tooÂ muchÂ salt thatâs bad for our hearts but apparently also tooÂ little.
Not all of this surprised me, because many practitioners of natural medicine have long held the view that advice on salt intake should be individualizedâand not simply be âless is bestâ for everyone. So I called the studyâs lead author, Martin J. OâDonnell, MB, PhD, an associate clinical professor of medicine at McMaster University in Canada, to learn more about the research.
SHAKING UP CONVENTIONAL WISDOM
Dr. OâDonnell told me that his studyâpublished in November 2011 inÂ Journal of the American Medical Associationâis the first large study to report potential heart health risks for both low and high salt intake in a single study.
Dr. OâDonnell and his colleagues examined data from nearly 29,000 men and women (all age 55 or over) from 40 countries who either had heart disease or were at increased risk for it because of prior history and co-morbidity factors such as diabetes. They looked at how much sodium was excreted in their morning fasting urine (so it wasnât self-reported salt intake) at the start of the study. The participants were not aware that their salt consumption was being measured, nor were they asked to raise or lower their intakeâthey just ate the amount that they normally ate.
What the researchers found was that, over four years, those who consumed higher-than-average amounts of saltÂ andÂ those who consumed lower-than-average amounts of salt experienced more heart problems (including deaths) than those with an average intake.
Itâs worth noting that the âaverageâ salt consumption among participants in this studyâestimated between 4,000 mg and 6,000 mg per dayâis much higher than the recommended upper limits of 1,500 mg per day (the advice of the American Heart Association) or 2,300 mg per day (the recommended dietary guideline from the US Department of Agriculture). And yet in this study it was the people who consumed this much salt who had the least number of heart problems.
The study showed that those with the highest and lowest amounts of sodium excretion had the highest risk. For example, those who consumed more than 8,000 mg daily were at a 50%-to-70% higher risk of suffering a cardiovascular event over the four-year period, compared with the âaverageâ salt group. And, not quite as alarming but still of concern, among those whose daily salt intake was between 2,000 mg and 3,000 mg, the likelihood of dying from a cardiac event related to congestive heart failure rose by 20%, compared with the âaverageâ salt group.
Now, itâs important to note that patients who ate the least amount of salt might have been doing so because they were at very high risk for disease and their doctors had insisted that they cut back severely on salt. In other words, their risk uptick might not be due to their salt intake (or their salt intake alone), but also due to poor health. âWe did some analysis to address this issue, but we canât exclude this possibilityâlarger clinical trials will be the only way to truly answer this question,â said Dr. OâDonnell.
The mystery isâhow could consuming a low amount of salt increase cardiovascular risk? There may be several potential reasons for this, Dr. OâDonnell said, but the most prominent hypothesis is that lower salt intake activates the bodyâsÂ renin-angiotensin system, which results in narrowed blood vessels, which of course makes it harder for blood to flow to and from the heart.
WHATâS THE SALT SOLUTION?
This studyâand others that have recently shown that similarly negative health effects may be associated with a low-salt dietâcaught the attention of the government. Congress has already put on hold its plans to legislate lower sodium levels for school lunches, requesting more information from the US Department of Agriculture before putting it to vote. Dr. OâDonnell said that there is âan urgent need to establish a safe range for sodium intake.â
In terms of how much saltÂ youÂ should eat, talk to your doctor about your particular risk factorsâand remember that the jury is still out.
Source:Â Martin J. OâDonnell, MB, PhD, associate clinical professor of medicine, McMaster University, Hamilton, Ontario, Canada.