The recent New York Times article ‘No Benefit Seen in Sharp Limits on Salt in Diet’ should not make you run to your favorite restaurant to catch a salty meal. Sodium is very necessary for health and is found in most of our foods, but just how much (or how little) should be a part of our diets is not so easy to nail down.
This article, and the research cited, brings into question the value of the lowest level of sodium currently recommended by the US Department of Health and Human Services and the US Department of Agriculture — daily sodium intake to less than 2,300 mg per day, and 1,500 mg per day for high-risk subpopulations including persons older than 51 years, Blacks, and persons with hypertension, diabetes, or chronic kidney disease (CKD). Currently, few Americans reach these sodium targets. In fact, on average we consume 3,400 mg of sodium per day.
So, who should be restricting their sodium, and what does watching the salt do for your health?
High Blood Pressure
Patients at risk for CKD with hypertension should not be phased. Low sodium diets can benefit them in a number of ways. High blood pressure currently affects approximately 72 million Americans. Even among those who are treated with medications, over 30% have a blood pressure above the widely recognized target of less than 140/90 mm Hg. Controlling blood pressure lowers the risk of stroke, coronary heart disease and kidney disease. Many studies have shown the benefit of reducing sodium intake to reduce blood pressure.
Dietary Sodium and CKD
Two small studies suggest that reducing sodium intake can decrease a marker of kidney damage — proteinuria — in patients with CKD, with or without diabetes. Most patients with CKD are salt sensitive, or their blood pressure increases with more salt intake. The National Kidney Foundation’s Kidney Outcomes Quality Initiatives CKD US Commentary on the 2012 KDIGO Clinical Practice Guideline for Management of Blood Pressure in CKD recommends a dietary sodium target of less than 2,000 mg (in press). This 2,000 mg level is also recommended by the World Health Organization.
But how low is too low?
In general, there are patients who are dehydrated and need more fluid and sodium intake. Also, there are rare patients with CKD and what doctors call salt-wasting nephropathy. These people require more sodium intake than is generally recommended because of excess urinary losses of sodium.
Other studies have shown people with heart failure treated with diuretics or “fluid pills” and blood pressure medicines have an increased risk of hospitalization and even death if they have very low sodium intake. People with heart failure have to delicately balance their sodium — too much salt in the diet may result in fluid in the lungs or heart failure; too little may impair blood flow to the vital organs the brain, heart, and kidneys.
The fact is, while there is still debate surrounding optimal sodium intake, most experts agree that we consume too much. Should we all aim for a diet with 1,500 mg of sodium or less? Probably not. Besides, sodium is so ubiquitous that if one is eating a truly low-sodium diet, it probably means they are not eating very much food at all.
No matter how you look at it, this article is big news, showing a positive relationship between higher sodium intake and cardiovascular disease (CVD) risk and all-cause mortality. However, the researchers also conclude that there is insufficient evidence to recommend lowering sodium intake below 2,300 mg a day because they are uncertain if it increases or decreases risk of CVD outcomes.
We should be concerned that the take-away message from anyone reading the NYT’s article is that reducing sodium can be bad for your health. In contrast, a careful read of the report makes that assumption less clear. More research is needed on this topic and as an organization we support further investigation in this arena.
Dr. Joseph Vassalotti is the National Kidney Foundation’s Chief Medical Officer