This is the second article in a two-part series on salt.
Last week, we discussed the potential negative effects of high sodium levels and low sodium levels, or the extremes. As I mentioned in last week’s article, the “extremes” of greater than 6,000 mg and less than 3,000 mg per day may increase the risk of cardiovascular events and all-cause mortality. However, the Prospective Urban Rural Epidemiology study on which these conclusions are drawn was significantly flawed. So don’t start using the salt shaker just yet without impunity. The bigger picture is that high sodium levels are dangerous and the low sodium levels used in this study likely are not.
Ironically, the sodium guidelines from a variety of health organizations range from recommendations of less than 1,500 mg per day to recommendations of less than 2,300 mg per day. Still, the average American takes in over 3,300 mg per day, with potentially disastrous health consequences. Theoretically, very low sodium levels – there’s no consensus on what those levels would be and the previous study does not help to shed light on that level – could potentially be harmful, but less than 1 percent of 100,000 people reached even the strictest of sodium levels (<1,500 mg per day). What we do know is the potential impact of higher levels. This week, we will continue to examine the latest research on sodium intake, in light of recent headlines that highlight disparities in medical opinions on sodium intake.
Blood pressure effect
Last week, we introduced the PURE study, which examined sodium intake by analyzing estimates of daily urinary sodium excretion extrapolated from once-a-day morning excretions. In another analysis involving the PURE study, results showed that those who excreted higher levels of sodium, greater than 5,000 mg a day in this case, had a substantially greater risk of high blood pressure (1).
Meanwhile, those who excreted 3 to 5 grams had a modest risk increase, and those who excreted the lowest amount, less than 3,000 mg, had no increased risk. This also involved over 100,000 participants. Potassium showed a positive impact; the greater amount of excretion, the lower the systolic (top number) blood pressure. The researchers concluded that those who were older, those who consumed more sodium and those with hypertension (high blood pressure) were more likely to experience a rise in their blood pressure.
However, in the NUTRICODE study, a meta-analysis (a group of 103 studies), results showed that there were over 1.5 million cardiovascular deaths in 2010 that were associated with higher sodium consumption (2). In this study, higher consumption meant greater than 2,000 mg of sodium per day. This number of deaths is based on a global scale involving 66 countries. The reason the cutoff for high sodium was lower than the other studies was that the researchers used the World Health Organization criteria. They calculated that nearly 1-in-10 cardiovascular deaths could be attributed to sodium intake. This is a sobering study that follows others showing similar results with sodium intake and cardiovascular disease.
Effects of reducing sodium
What happens when we reduce salt? Do we have Armageddon? Not quite. In fact, in a recent British analysis of the Health Survey for England, the results showed that reducing sodium by 1,400 mg per day significantly reduced the risk of cardiovascular events (3). The number of deaths from stroke decreased by 42 percent. There were also significant reductions in blood pressure and ischemic heart disease. The term ischemic heart disease is an umbrella term that means reduced blood supply to the heart, usually caused by atherosclerosis, or plaque in the arteries. It is the most common form of heart disease.
This study used 24-hour urinary excretion rates, the gold standard for estimated sodium consumption. Unlike studies mentioned previously, these rates were not estimated. However, there were issues with confounding factors (uncontrolled variables) not being taken into account. This was not a study without flaws, either. Having said this, decreasing sodium intake by a significant amount in the diet might actually have positive benefits. We need a randomized controlled trial to confirm this.
Sodium impact on children
Sodium may have deleterious effects in children. In a recent report from the Centers for Disease Control, 90 percent of kids take in too much salt. These children are between the ages of 6 and 18. Almost 17 percent, or 1 in 6 kids ages 8 to 17, have high blood pressure. This does not mean sodium is directly correlated, since it is not a study. However, it is likely to be a contributor. A handful of foods including chicken nuggets, chips, breads, cold cuts, sauces and soups. contribute 40 percent of our sodium intake. The good news is that the government is going implement sodium reduction in school food 50 percent by the year 2022. However, much of the problem also occurs at home.
You may not be able to look at sodium alone without considering the sodium-potassium ratio. In an observational study, results showed that those with a high sodium-to-potassium ratio had an almost 1.5 times greater probability of all-cause mortality and cardiovascular disease-related death than those with a much lower sodium-to-potassium ratio (5). The group that had higher sodium-to-potassium ratios also had a two-times increased risk of having ischemic heart disease. The duration was a strong point of this study, with almost 15 years of follow-up data. There were over 12,000 patients. It is believed that potassium gets its beneficial effects by activating nitric oxide, which causes vasodilation of arteries and, thus, may lower blood pressure.
While it is possible to get too little salt, it is rather unlikely and rare, especially with a plant-based diet. A diet rich in leafy green vegetables provides about 600-700 mg of sodium by itself, as well as high amounts of potassium. Low sodium is less than 140 mg per serving. But caveat emptor (buyer beware): serving sizes on labels can be deceiving, especially when you might eat more than one serving.
Reducing sodium is an easy way of helping to reduce acute (short-term) symptoms, such as dehydration, bloating and weight gain, while decreasing the risk of many diseases in the long term. Focus on decreasing the sodium, as the British study showed the positive impact on cardiovascular disease. And, if you have adolescents, preteens and teens, try to help reduce their sodium intake as well. Concentrate on increasing potassium intake and decreasing the sodium intake to optimize your sodium-to-potassium ratio.
(1) N Engl J Med. 2014;371:601-611. (2) N Engl J Med. 2014;371:624-634. (3) BMJ Open. 2014;4:e004549. (4) www.cdc.gov. (5) Arch Intern Med. 2011;171:1183-1191.
Dr. Dunaief is a speaker, author and local lifestyle medicine physician focusing on the integration of medicine, nutrition, fitness and stress management. For further information, go to the website www.medicalcompassmd.com and/or consult your personal physician.