Sodium

What is sodium (natrium)?

Sodium is a mineral that is an essential nutrient to human life and health.

The chemical symbol for sodium is Na.

Sodium Functions in the Body

Some important functions of sodium in the human body:

1. Sodium, along with chloride and potassium, helps to maintain electrical charge across the cell membranes in the nerve tissue and thus enables proper functioning of the nerves, muscles and heart ^[1].

2. Sodium enhances the absorption of chloride, glucose, amino acids and water from the small intestine into the blood, and the absorption of glucose and amino acids from the blood into the cells ^[1]. The sodium content of beverages probably does not significantly affect water absorption ^[3,4].

3. Sodium promotes water retention in your body. An increase of the dietary sodium intake from 2 to 5 grams per day can increase the amount of water in your body by about 1 liter ^{[2: Figure 2-2]}.

4. Sodium is involved in the regulation of blood volume and pressure. A drop of blood volume or pressure–for example, due to massive bleeding or dehydration–triggers the release of the adrenal hormone aldosterone, which stimulates sodium and thus water retention in the kidneys, which helps to maintain the blood volume and pressure. An increase of blood volume or pressure–for example, due to water drinking or salt intake–decreases the aldosterone release, which results in increased sodium and water excretion in the kidneys ^[1].

What is the recommended daily sodium and salt intake?

American Heart Association recommends less than 1.5 gram of sodium (3.8 g of salt) to everyone, unless prescribed otherwise by a doctor ^[5].

The estimated minimal requirement of sodium for adult Americans in a wide range of physical activities and climates is about 200 mg of sodium (500 mg of salt) per day ^[13]. Patients with heart and kidney diseases, diabetes, hormonal disorders or high or low blood pressure should ask their doctors about the optimal sodium intake.

Sodium Absorption and the Regulation of the Normal Blood Sodium Concentration

In general, the more sodium you ingest, the more of it is absorbed from the small and large intestine. The blood serum sodium concentration is normally maintained at a certain level between 136 and 145 mmol sodium per liter. When you consume less sodium than you need, the blood sodium concentration falls slightly, which triggers the release of the adrenal hormone aldosterone, which reduces the sodium excretion in the kidneys. When you ingest more sodium than you need, the blood sodium concentration raises slightly, which inhibits the release of aldosterone, which results in an increased sodium excretion in the kidneys.

Sodium absorption may be increased in chronic pancreatitis with steatorrhea. Sodium and hence water absorption, often decreased in chronic alcoholics, may result in diarrhea ^[7].

Foods High in Sodium

The main source of the dietary sodium is salt (sodium chloride or NaCl), and to a smaller extent baking soda (NaHCO₃) and food additives monosodium glutamate (MSG), sodium diphosphate (in baking powder), sodium alginate and other substances with “sodium” or “Na” in their names.

• Beverages relatively high in sodium: certain sport and energy drinks and mineral waters, coconut water, tomato juice ^[6].
• Medications high in sodium include sodium bicarbonate (an antacid), sodium phosphate (a laxative), naproxen sodium (an analgesic), diclofenac sodium, cromolyn sodium, sodium nitropruside and others. The sodium content 5 mg or larger per a drug dose should be mentioned in the drug information leaflet.
• Human breast milk contains about 170 mg sodium/liter ^[6]. The Adequate Intake (AI) for sodium for 0-6 months old infants is 120 mg/day and for 7-12 months old infants is 370 mg/day ^[1].

Picture 1. Examples of foods high in sodium

Chart 1. Foods High in Sodium (>140 mg/serving)
SALT, BAKING SODA and POWDER	Sodium (mg)
Table salt – NaCl (1 tsp, 6 g)	2,300
Baking soda – NaHCO3 (1 tsp, 4 g)	1,200
Baking powder – sodium aluminium sulfate (1 tsp, 4 g)	500
Table salt – NaCl (1 g)	400
ANIMAL FOODS
Fish, dried, salted (3 oz, 85 g)	1,700-6,000
Soup, dry mix with water (1 cup, 237 mL)	3,300-3,800
Shrimps, breaded (7 pieces, 165 g)	1,500
Fish sauce (1 tbsp, 18 g)	1,400
Ham, pork (3 oz, 85 g)	1,100
Beef, corned (3 oz, 85 g)	1,000
Burrito with beef and cheese (150 g)	1,000
Pizza (1 serving, 150 g)	800-1,000
Beef stew, canned (1 cup, 237 mL)	900
Cheeseburger, double patty (160 g)	900
Crabs (3 oz, 85 g)	200-900
Cheese: American or Swiss w disodium phosphate (2 oz, 57 g)	800
Frankfurter, chicken (1 frank)	600
Salami (beef or pork) (2 oz, 57 g)	600
Cheese: edam, gouda, feta (2 oz, 57 g)	400-600
Gravy (3 oz, 85 g)	500
Cottage cheese (1/2 cup, 120 mL)	500
Bacon (1 oz, 28 g)	500
Sardines, canned (3 oz, 85 g)	400
Pudding, chocolate (1/2 cup, 120 mL)	400
Oysters (3 oz, 85 g)	400
Shrimps (3 oz, 85 g)	190
Egg (1 whole, 50 g)	150
Milk (1 cup, 237 mL)	145
PLANT FOODS
Eggplant, pickled (1/2 cup, 120 mL)	1,100
Pretzels (2.1 oz, 60 g)	1,000
Soy sauce (1 tbsp, 18 g)	1,000
Miso (1 oz, 28 g)	1,000
Cucumbers, pickled (1/2 cup, 120 mL)	900
Tofu (1 oz, 28 g)	800
Tomato juice, canned, salt added (1 cup, 237 mL)	700
Beans, baked, canned (1/2 cup, 120 mL)	500
Potato chips, salted (2 oz, 57 g)	400
Olives, canned (1 oz, 28 g)	400
Salad dressing (1 oz, 28 g)	200-400
Mineral water (1 cup, 237 mL)	0-400
Cereals, ready-to-eat, prepared (1 cup, 237 mL)	100-300
Bagel (4″ dia)	300
Catsup [ketchup] (1 oz, 28 g)	300
Tomato sauce, canned (2 oz, 57 g)	300
French fries (117 g)	300
Cake, chocolate (1 piece, 100 g)	300
Pie, cherry (1 piece, 120 g)	300
Sport drinks (1 cup, 237 mL)	110-275
Coconut water (1 cup, 237 mL)	250
Energy drinks (8.3 fl oz, 247 mL)	200
Peanuts, salted (1 oz, 28 g)	200
Crackers, salted (1 oz, 28 g)	200
Popcorn, salted (2 cups, 475 mL)	200
Mushrooms, canned (8 caps, 47 g)	200
Yeast extract spread (1 tsp, 6 g)	200
Bread, white or rye (1 slice, 30 g)	200
Beet greens, cooked (1/2 cup)	150
Beets, cooked (1/2 cup)	150

Chart 1 source: USDA.gov ^[6]

Sodium in Sport Drinks And Oral Rehydration Solutions (ORS)

Sodium is used in sport drinks and oral rehydration solutions in order to:

• Improve their taste and therefore to encourage drinking
• Promote water retention in the body
• Prevent a drop of blood sodium levels (dilutional hyponatremia or water intoxication) when large amounts of fluid are needed.

Sport drinks that contain 460-1,150 mg of sodium/liter (110-275 mg/8 fl. oz) are effective in preventing hyponatremia during hard exercise lasting more than 2 hours, such as marathon or triathlon, according to European Food Information Council ^[17] and the Peak Performance website ^[18]. NOTE: Many commercial sport drinks do not contain enough sodium to prevent hyponatremia ^[15].

Oral rehydration solution (ORS) by WHO/UNICEF contains 410 mg of sodium per cup (8 fl. oz, 237 mL) ^[19]. Commercial oral rehydration solutions with similar or somewhat lower sodium contents are available in stores. ORS is mainly used to treat dehydration in infants and small children up to 4 years of age with diarrhea.

Dangers of Acute High Sodium (Salt) Intake

A large amount of sodium taken at once may trigger nausea, vomiting, abdominal cramps or diarrhea ^[1]. The absorption of large amounts of sodium, for example, after using highly concentrated salt solution to induce vomiting as a first aid measure in poisoning, may result in hypernatremia, which may be fatal ^[36].

Dangers of Chronic High Sodium (Salt) Intake

High Blood Pressure

According to the INTERSALT epidemiological study (1984-97), which included 10,079 adults 20-59 years of age from 32 countries, the estimated effect of a sodium intake higher by 2.3 g/day was higher blood pressure by 3-6/0-3 (upper/lower) mm Hg ^[45].

Salt Sensitivity and Blood Pressure

Salt sensitivity means an increase of the systolic (upper) blood pressure by 10 or more mm Hg upon acute intake of salt. About 50% of the U.S. population may be salt sensitive ^[26]. Salt sensitivity tends to increase with age and body weight and decrease with potassium intake and physical activity ^[22,28]. Salt-sensitivity can be also influenced by genetics and race; Afro-Americans tend to be more salt-sensitive than American whites ^[22]. Individuals with diabetes, high blood pressure and chronic kidney diseases tend to be more salt-sensitive ^[22].

Coronary Heart Disease and Stroke

According to several systematic reviews, there is CONFLICTING EVIDENCE about the effect of high salt intake on cardiovascular disease ^[1,20,24,41].

Gastric Cancer

Epidemiological and prospective studies in eastern Asia suggest that long-term intake of salted, smoked and pickled foods, which are high in sodium, is associated with increased risk of gastric cancer, especially in individuals with chronic inflammation of the stomach (atrophic gastritis) caused by the bacteria Helicobacter pylori ^[1,37,38,40].

Osteoporosis

It is not known if high sodium intake increases the risk of osteoporosis ^[1,33].

Low-Sodium Diet

In general, low-sodium diet means consuming less than 2 g of sodium (5 g salt) per day.

A low sodium diet is intended to reduce water retention and swelling in congestive heart failure, kidney failure, liver cirrhosis and certain hormonal disorders, such as Cushing syndrome (in adrenal or pituitary gland tumor) or hyperaldosteronism. It is also often advised to individuals with high blood pressure, coronary heart disease and diabetes mellitus.

Tips for low-sodium diet:

• Do not add salt at table.
• Avoid processed, cured, smoked and canned meats and fish, canned vegetables, pre-prepared soup mixes, snacks (salted chips or peanuts), fast foods, cheeses, sport and energy drinks and mineral waters and products containing more than 100 mg of sodium per serving, or containing monosodium glutamate (MSG), sodium alginate, nitrate, diphosphate or other substances with “sodium”, “soda” (baking soda or sodium bicarbonate) or “Na” in their names.
• Check if antacids, supplements or drugs you use contain more than 100 mg of sodium and ask your doctor for alternatives.
• Before using salt substitutes containing potassium chloride, speak with your doctor, since potassium overdose can be life-threatening.
• Low-sodium diet does not likely lead to sodium deficiency.

Benefits of Low Sodium (Salt) Intake

A Decrease in Blood Pressure

Changing a diet from high-sodium (>2,000 mg/day) to low-sodium (<2,000 mg/day) reduces the systolic (upper) blood pressure in adults and children by about 3 mm Hg, in average ^[20], but it is not clear if this has any beneficial health effect ^[21]. The effect of lowering dietary sodium on blood pressure does not seem to be dose-dependent ^[20].

In a DASH-sodium trial, an average systolic (upper) blood pressure in a low-salt intake group (2.9 or less g salt/day) was 6.7 mm Hg lower than in a high-salt intake group (8.9 or more g salt/day) ^[23].

Lower sodium intake has been associated with lower risk of stroke and fatal coronary heart disease in adults ^[20].

Coronary Heart Disease and Stroke

Authors of 2 systematic reviews from 2002 and 2014 have concluded that currently there is INSUFFICIENT EVIDENCE to claim that reduced salt intake is associated with less cardiovascular diseases and deaths ^[25,26]. According to another 2014 review, high sodium intake is associated with increased risk of coronary heart disease only in individuals with hypertension ^[35].

Gastric Cancer

There is SOME EVIDENCE that lowering salt intake may reduce the risk of gastric cancer ^[39].

Kidney Stones

There is INSUFFICIENT EVIDENCE about the effect of low-sodium diet in prevention of kidney calcium stones ^[29,30,31].

Asthma

There seems to be NO EVIDENCE that low sodium intake would improve symptoms of asthma over long periods of time ^{[34,42,43,44]}.

Low-Sodium and Sodium-Free Foods

The US Food and Drug Administration (FDA) has determined the criteria for sodium sodium-related claims on the food labels ^[14]:

• “Low in sodium:” 140 mg of sodium or less per serving
• “Very low in sodium:” 35 mg of sodium or less per serving
• “Sodium-free:” less than 5 mg of sodium per serving
• “Reduced sodium:” contains at least 25% less sodium than the regular foods
• “Light in sodium:” contains at least 50% less sodium than the regular foods
• “No salt added” or “unsalted” for foods with no added sodium

Chart 2. Foods Low in Sodium (<140 mg/serving)
FOODS LOW in SODIUM (35-140 mg/serving)	Sodium (mg)
Low-sodium salt (1 tsp, 6 g)	Check the product label.
Milk (1 cup, 237 mL)	100-140
Fish: bass, cod, herring, mackerel, salmon, trout; oysters (3 oz, 85 g)	40-140
Cereals, ready-to-eat, certain products (30 g dry > 1 cup, prepared)	0-140
Yogurt (6 oz, 170 mL)	100-130
Celery (1/2 cup, 120 mL)	70
Chicken, turkey (3 oz, 85 g)	65
Carrots (1/2 cup, 120 mL)	45
Sweet potatoes (1 potato, 155 g)	40
FOODS VERY LOW in SODIUM (35 mg or less/serving)
Lettuce, green leaf (1 cup, 237 mL)
Avocado (1 cup, 237 mL)
Beans: green, pinto, snap, white, yellow; chickpeas (1/2 cup, 120 mL)
Municipal (tap) or bottled water (1 cup, 237 mL)
Grains: barley, bulgur, corn grits, couscous (1 cup, 237 mL)
Vegetables: asparagus, broccoli, Brussel’s sprouts, cabbage, cantaloupe, cauliflower, collards, garden cress, kale, kohlrabi, mustard greens, okra, potatoes, rutabagas, squash (winter), tomatoes, turnip (1/2 cup, 120 mL)
Applesauce, canned (1 cup, 237 mL)
SODIUM-FREE FOODS (<5 mg/serving)
Potato chips, unsalted (2 oz, 57 g)
Honey (1 tbsp, 21 g)
Lettuce, romaine (1 cup, 237 mL)
Vegetables: cucumber, eggplant, peppers, pumpkin, squash (summer) (1/2 cup, 120 mL)
Peanuts, pine nuts (1 oz, 28 g)
Legumes: beans (black, green, kidney, lima, mung, navy, snap), lentils, split peas, cowpeas (1/2 cup, 120 mL)
Butter, unsalted (1 tbsp, 14 g)
Onions (1 large slice, 38 g)
Cocoa powder (1 tbsp, 5g)
Dates, medjol (2 oz, 57 g)
Puffed rice (1 cup, 237 mL)
Blackberries, blueberries, raspberries (1/2 cup, 120 mL)
Fruits; apple, apricot, banana, berries, cherries, grapes, grapefruit, kiwifruit, mango, nectarine, orange, papaya, pear, peach, pineaple, plums, watermelon (150 g)
Nuts: almonds, filberts, hazelnuts, pecans, walnuts (1 oz, 28 g)
Oils: canola, corn, olive, peanut, safflower, sesame, sunflower (1 tbsp, 14 g)
Vinegar, cider (1 tbsp, 14 mL)

Chart 2 source: USDA.gov ^[6]

Sodium Interactions With Other Nutrients

High sodium intake increases calcium excretion in the kidneys, but there is insufficient evidence of this effect on kidney calcium stones or osteoporosis ^[30].