Probably the first thing people think of when they hear the words high blood pressure is salt. From health professionals to health organizations, we’ve been told to watch our salt intake for better health. And in particular, to reduce sodium. But is salt really that bad for you?
Sodium and blood pressure are definitely related. Eating excess salt makes you thirsty leading you to crave fluids. The extra fluids water down the amount of sodium in the blood. In turn, blood volume, and as a result, blood pressure, increases until the excess sodium (and water) can be excreted in urine.
Nearly one in four adults have high blood pressure, or hypertension, which is defined as a blood pressure ≥140/90 mmHg. The top number is the pressure in the arteries when the heart beats and the lower number is the pressure in between beats. The concern of high blood pressure is such that every corner drug store has an automated machine. This is because chronic hypertension is associated with increased chances for kidney and heart disease, stroke and early death.
We Can’t Live Without Sodium
While sodium got its bad name because of its close association with hypertension, it’s also vital to human body functioning. Sodium regulates the volume of our body’s cells and is needed for nerve impulses. It’s also involved in transporting blood sugar, amino acids and other nutrients into cells, as well as for muscle contraction. And for the small number of people with low blood pressure (hypotension), an increase in sodium intake is often recommended. As a result, we need sodium to live.
The human body does not have the capacity to store sodium for a long time, so the only way to get sodium is by eating it. Any excess is removed by the kidneys and into the urine. But sodium isn’t readily available in many natural foods. For example, a tomato has 5 mg, and apple has 1 mg, an egg has 124 mg and a chicken thigh has 87 mg of sodium.
While tastes buds can change based on your diet, humans naturally crave salt. This may be an evolutionary advantage given we can’t store sodium and most natural foods have low amounts. A desire for salty food was helpful over the millennia to ensure we had enough to keep us alive. But now, salt is plentiful and that evolution advantage isn’t needed.
Where do we get our salt from?
You probably have a saltshaker close to your dining room table. Or at least in your spice cabinet. However, nearly 90% of salt intake comes from foods. And almost all of that is from processed foods. For example, a cucumber has less than 3 mg of sodium, while a pickle can have over 1200 mg. Very little of our salt intake comes from salt being added while cooking or at the dinner table.
Salt is used in foods for a variety of reasons. As a preservative it increases shelf-life and fends off bacteria. And the more processed a food is, the more salt is added. It’s also required for making cheese and bread. It also adds taste and texture to foods taking advantage of our natural craving. Of note, many foods can be high in salt without really tasting salty. This includes cakes and baked goods, and even some mineral waters.
The average adult in the US consumes approximately 3700 mg/day. In Canada, it sits at about 2700 mg/day. However, dietary guidelines for sodium intake vary among organizations. Health Canada has some of the most stringent guidelines recommending a daily maximum of 1500 mg (half a teaspoon of salt). This is in contrast to the World Health Organization maximum is 2000 mg per day and The National Academy of Sciences, which suggests the upper daily target be 2300 mg.
Reducing Sodium Intake
For people who have hypertension, reducing high-sodium foods is one of the top recommended strategies (along with regular exercise and weight management). Robust randomized trials consistently show diets low in sodium are effective at reducing blood pressure. Probably the most popular low-sodium diet is the DASH diet (Dietary Approaches to Stop Hypertension), which encourages whole grains, fruits, vegetables and low-fat dairy.
However, there’s been much debate about the value of widespread sodium reduction. The first concern is guideline targets are quite low and may be unrealistic in our current food environment. As individuals, we have very little control on selectively reducing sodium, since it’s so common in many food products. Without targeted legislation for the food industry to reduce salt use in food production, it’s unlikely the average sodium intake will ever be close to the guideline targets.
Eur Heart J, ehaa947, https://doi.org/10.1093/eurheartj/ehaa947
Lower Sodium and Long-term Health
The second, and perhaps most contentious, is evidence questioning the relationship between sodium intake and risk for disease. There’s ample consensus a high sodium diet is associated with high blood pressure. And there’s plenty of evidence that lowering blood pressure with medications lowers chances for heart disease, stroke and early death. Therefore, many assume lowering salt intake will also lower disease risk. For example, if A causes B, and B causes C, then A must cause C too. But this may not be the case when it comes to sodium.
A number of studies have suggested sodium levels about 2-3 times current guidelines pose the lowest risk to health. And levels close to the guidelines may actually be associated with increased risk creating a sort of U-like shaped curve. In a study of 181 countries, those with the greatest life expectancy tended to have the highest dietary sodium intakes. While those countries with intakes close to, and below, the recommended guidelines had lower life expectancy.
But whether you’ll benefit from reducing sodium may depend on what your blood pressure is to begin with. If you have hypertension and a high sodium intake (more than 5000 to 6000 mg/day), cutting back may be beneficial.
However, there’s a major caveat to these studies in that they’re all observational. Unlike studies of medications that lower blood pressure, we don’t have randomized studies looking at the long-term effects of sodium reduction in the diet. That being said, most observational studies suggest a diet low in sodium may have negative effects.
Is it low sodium, high potassium, or both?
Conducting long-term diet studies is challenging. When we look to change one thing in our diets, it’s hard not to change anything else. For example, low sodium diets restrict processed foods. Processed foods contains additives that have been shown to have negative effects on health. Low sodium diets are also high in fruits and vegetables, making them high in potassium. Potassium is often overlooked in the sodium debate, but potassium helps to regulate sodium levels and is associated with lower blood pressure. So it’s not quite clear if the benefit of a low sodium diet is due to reduced sodium, reduced processed foods, increased potassium, or all of that together.
While the current data are not conclusive, population-wide reductions in sodium intake may be hard to accomplish and may not offer expected long-term health benefits. For certain individuals, a low sodium diet may be advised by a health professional. But for most people, focusing on one’s overall diet, as opposed to one specific nutrient is recommended. A high quality diet consists of limiting processed foods and focusing on whole foods such as fruits and vegetables, nuts, fish, unprocessed meats and dairy.
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