My Take on Salty Science
A widely publicized recent scientific review seems to put sodium-sensible diets on shaky ground. Here’s why Cooking Light is sticking with the Dietary Guidelines.
By Sidney Fry, MS, RD
Flash back to the mid-1980s when the cholesterol scare hit. Eggs made the cover of Time magazine as America’s Nutrition Enemy #1. But after a massive scientific dive into the nitty-gritty, health professionals began to realize that not all cholesterol behaved the same way in the body, and that some even had beneficial effects. Dietary cholesterol in moderation was given the ok and eggs (along with other high cholesterol foods like shrimp) are back on the menu.
To many, nutrition science seems like that old saw about weather: If you don’t like it, just wait a few minutes, and it will change.
Sodium is the latest nutrient to get the flip-flop treatment. Health professionals and policymakers have for years recommended limiting daily intake to 2,300 mg (a teaspoon). The 2010 Dietary Guidelines suggest even less for anyone with hypertension, and those risk of high blood pressure, which includes people over age 50 and African Americans. But salt advocates point out that the scientific evidence linking sodium to cardiovascular disease is shaky at best. This group got a big boost last month when the American Journal of Hypertension released a widely publicized review of the scientific literature that seemed to disprove the claims of most health authorities. The conclusion: No strong body of evidence exists that links lower sodium diets to cardiovascular disease and death. Cue the splashy cover story, this time from Scientific American.
So, does that mean we can give the Dietary Guidelines and their 2,300mg limit the heave-ho? No, and here’s why:
- High blood pressure typically develops over many years. And years of uncontrolled high blood pressure increase your risk of serious health problems, including heart attack and stroke. The higher the blood pressure, the greater the risk of these events. Studies have shown that dramatically lowering salt intake results in a blood pressure drop. In many of these studies, the greatest effect is found in the overweight, older individuals, and those with high blood pressure—the people today’s healthy adults may become.
- Most sodium studies are observational, meaning that they track salt consumption and blood pressure over a relatively short period of time. Information is often based on the participants’ ability to recall what they normally eat. Memory can be fuzzy. Most studies that actually alter participants’ diets to reduce sodium (and there are fewer of them) last only 30 days—not long enough to truly tell a difference.
- About 10 to 25% of the population is salt sensitive, meaning they are more susceptible to a spike in blood pressure after eating a lot of salt. The connection between salt and high blood pressure in those who are more salt sensitive is undeniable. But there’s no routine method to test for salt sensitivity, other than to use hypertension as a marker of sensitivity. By then, of course, it’s too late.
It’s important to note that the authors of the American Journal of Hypertension review did not conclude that reducing salt consumption is ineffective. They concluded that our interventions and efforts to lower sodium have had little effect on cardiovascular disease. In other words, public health measures haven’t had much effect. With restaurants and processed foods providing nearly 80% of the sodium we consume, it’s little wonder.
So how could we establish a conclusive link between consuming less sodium and reduced rates of cardiovascular disease? First we’d have to design a study that assigns patients to either a high- or low-sodium diet, and make them follow it for years. Then we’d have to enforce and monitor their diets, measure their blood pressure, and record any cardiovascular events that might occur. We’d need hundreds—if not thousands—of people to participate. Such a study is never going to happen, largely because no investigator would ever get funds to put people on a potentially fatal super-high sodium diet.
It’s true that no study has ever found a direct association between reduced sodium diets and reduced rates of cardiovascular disease with sodium as the sole causing factor. The DASH diet is often cited as a successful low-sodium diet program that can help reduce cardiovascular disease risk, but the DASH diet isn’t exclusively focused on sodium reduction. It’s also rich in fruits, vegetables, and whole grains, which all contain other essential nutrients like calcium, potassium, and magnesium… all of which help lower blood pressure.
DASH points the way to a whole-diet approach to helping prevent cardiovascular disease. When people eat a balanced diet that emphasizes fruits, vegetables, lean proteins, heart healthy fats, and low fat dairy in sensible portions, moderating their sodium, calorie, and saturated fat intake (as we do here at Cooking Light), then sodium intake automatically trends downward, taking blood pressure rates with it. Add regular exercise to the mix, and heart health improves even more. As Cooking Light’s editor reminds us in his September 2011 editor's letter, “There are many possible reasons why a healthy diet is healthy. Don’t get hung up on one factor.”