“Low sodium” has two common meanings depending on the context. On a food label, it means the product contains 140 mg or less of sodium per serving. In a medical context, it refers to a blood sodium level below 135 millimoles per liter, a condition called hyponatremia. Both meanings matter for your health, but in very different ways.
Low Sodium on Food Labels
The FDA regulates exactly when a food manufacturer can print “low sodium” on packaging. A product qualifies if it contains 140 mg or less of sodium per standard serving size. For complete meals, the threshold is 140 mg or less per 100 grams of the product. You’ll also see a stricter claim, “very low sodium,” which means 35 mg or less per serving.
A quick way to evaluate any food is the percent Daily Value (%DV) on the Nutrition Facts panel. The FDA considers 5% DV or less per serving to be low, and 20% DV or more to be high. Since the daily reference value for sodium is 2,300 mg, a serving with 5% DV contains about 115 mg, while one with 20% DV packs around 460 mg. Scanning the %DV column is faster and more reliable than trying to judge milligram counts on their own.
How Much Sodium Most People Eat
The Dietary Guidelines for Americans recommend that adults consume less than 2,300 mg of sodium per day, roughly one teaspoon of table salt. The average American eats about 3,400 mg daily, nearly 50% over that limit. Children have even lower thresholds: 1,500 mg per day for ages 4 through 8, and 1,800 mg for ages 9 through 13.
Most of that excess doesn’t come from the salt shaker. CDC data shows that more than 40% of sodium intake comes from just ten food categories: breads and rolls, deli meats, pizza, poultry products, soups, sandwiches, cheese, pasta dishes, meat-based mixed dishes, and salty snacks like chips and pretzels. Foods that don’t taste particularly salty, like cottage cheese, sandwich bread, or packaged turkey breast, can be surprisingly high in sodium.
Why Sodium Affects Blood Pressure
Sodium plays a central role in how your body manages fluid balance. When you eat more sodium than your body needs, your kidneys work to excrete the excess. In people whose blood pressure is sensitive to sodium (a trait called salt sensitivity), this process doesn’t work smoothly. The traditional explanation is that extra sodium causes the body to hold onto water, expanding blood volume and forcing the heart to pump harder.
More recent research from the American Heart Association points to an additional mechanism. In salt-sensitive people, blood vessels fail to relax properly in response to higher sodium intake. Normally, when you eat more salt, your blood vessels widen slightly to accommodate the temporary increase in fluid. In salt-sensitive individuals, that relaxation doesn’t happen. The vessels stay constricted, and blood pressure rises. This vascular stiffness appears to be driven partly by changes in the cells lining blood vessel walls, which become stiffer when exposed to elevated sodium concentrations.
Who Benefits From a Low Sodium Diet
Reducing sodium intake lowers blood pressure in people with high or borderline-high blood pressure. That alone is significant, since high blood pressure is the leading modifiable risk factor for heart disease and stroke. But sodium reduction is also a core part of managing two other major conditions.
People with chronic kidney disease have reduced ability to filter and excrete sodium. Excess sodium leads to fluid buildup, which raises blood pressure further and accelerates kidney damage. In heart failure, the heart can’t pump efficiently enough to keep fluid circulating normally. Extra sodium causes swelling in the legs, abdomen, or lungs, and can trigger dangerous flare-ups. For both conditions, controlling sodium intake helps prevent the fluid overload that worsens the disease.
Reading Labels in Practice
Knowing the definitions is useful, but the real skill is spotting sodium in foods you eat regularly. Start with the %DV shortcut: aim for items at 5% DV or below, and flag anything at 20% or above. Pay attention to serving sizes, because a can of soup that lists 800 mg of sodium might define a serving as half the can.
Bread is a good example of how sodium adds up quietly. A single slice might contain only 150 mg, but if you eat four slices throughout the day in sandwiches and toast, that’s 600 mg from bread alone. The same stacking effect happens with condiments, cheese, and canned goods. No single serving looks alarming, but the daily total climbs fast.
Salt Substitutes: A Practical Option
Potassium-based salt substitutes replace some or all of the sodium chloride in regular salt with potassium chloride. Research shows these substitutes can lower blood pressure and reduce the risk of stroke. A large study following participants for nearly five years found slightly lower rates of strokes, major heart problems, and deaths among people using salt substitutes compared to regular salt. Notably, participants in the study were not more likely to develop dangerously high potassium levels, which had been a concern. That said, if you have kidney disease, your ability to excrete potassium is impaired, so potassium-based substitutes may not be appropriate for you.
Low Sodium in the Blood: Hyponatremia
The other meaning of “low sodium” is medical. A healthy blood sodium level falls between 135 and 145 millimoles per liter. When it drops below 135, the condition is called hyponatremia. This isn’t about eating too little salt. It’s usually caused by the body retaining too much water relative to sodium, which dilutes sodium concentration in the blood.
Common causes include certain medications (particularly water pills used for blood pressure), drinking excessive amounts of water in a short period, and hormonal conditions that affect how the kidneys handle water. Chronic illnesses like heart failure, liver disease, and kidney disease also increase the risk.
Mild hyponatremia can cause nausea, headaches, confusion, and fatigue. As levels drop further, symptoms escalate to muscle cramps, weakness, irritability, and restlessness. Severe cases can lead to seizures or coma. The condition develops either gradually, where symptoms may be subtle and easy to overlook, or rapidly, which is more dangerous because the brain doesn’t have time to adapt to the shifting fluid balance.
If you’ve had blood work showing low sodium, the concern is very different from dietary sodium restriction. Eating more salt is rarely the fix. Treatment depends entirely on what’s causing the imbalance, whether that’s adjusting a medication, treating an underlying condition, or managing fluid intake.