Chapter 10. Micronutrients Involved in Fluid and Electrolyte Balance
Sodium
Functions of Sodium
Sodium is vital not only for maintaining fluid balance but also for many other essential functions. In contrast to many minerals, sodium absorption in the small intestine is extremely efficient and in a healthy individual, all excess sodium is excreted by the kidneys.
The second notable function of sodium is in nerve impulse transmission. Nerve impulse transmission results from the transport of sodium cations into a nerve cell, which creates a charge difference (or voltage) between the nerve cell and its extracellular environment. Similar to how a current moves along a wire, a sodium current moves along a nerve cell. Stimulating a muscle contraction also involves the movement of sodium ions as well as other ion movements.
Sodium is essential for nutrient absorption in the small intestine and nutrient reabsorption in the kidney. Amino acids, glucose and water must make their way from the small intestine to the blood. To do so, they pass through intestinal cells on their way to the blood. The transport of nutrients through intestinal cells is facilitated by the sodium-potassium pump, which by moving sodium out of the cell, creates a higher sodium concentration outside the cell (requiring ATP). Sodium also helps regulate blood pressure and maintain acid-base balance.
Sodium Imbalances
Sweating serves as a homeostatic mechanism to regulate body temperature and plays a crucial role in maintaining fluid and electrolyte balance. Sweat primarily consists of water but also contains electrolytes, particularly sodium and chloride. Under normal environmental conditions (excluding hot and humid days), the loss of water and sodium through sweat is minimal, although it can vary significantly among individuals. It is estimated that engaging in high-intensity physical activity for approximately sixty minutes, such as playing a tennis match, can generate around one liter of sweat. However, the quantity of sweat produced is greatly influenced by environmental conditions. In general, a liter of sweat typically contains between 1 and 2 grams of sodium. This is why prolonged exercise sessions can lead to considerable sodium loss in some individuals. Moreover, demanding physical labor can result in significant sodium depletion through sweat. In either case, the lost sodium can be easily replenished through snacks or meals.
In athletes, hyponatremia, or a low blood sodium level, is not so much the result of excessive sodium loss in sweat, but rather drinking too much water. The excess water dilutes the sodium concentration in the blood. Illnesses causing vomiting, sweating, and diarrhea may also cause hyponatremia. The symptoms of hyponatremia, also called water intoxication (since it is often the root cause), include nausea, muscle cramps, confusion, dizziness, and in severe cases, coma and death. The physiological events that occur in water intoxication are the following:
- Excessive sodium loss and/or water intake.
- Sodium levels fall in blood and in the fluid between cells.
- Water moves to where solutes are more concentrated (i.e. into cells).
- Cells swell.
- Symptoms such as nausea, muscle cramps, confusion, dizziness, and in severe cases, coma and death result.
Hyponatremia in endurance athletes (such as marathon runners) can be avoided by drinking the correct amount and type of fluid. Sports drinks are better and are a good way to restore fluid, blood glucose levels, and electrolytes. For events lasting longer than 1 hr, aim for beverages containing 6-8% carbohydrates, 0.5-0.7 g of sodium and 0.8-2.0 g of potassium per litre of water.[1],[2] If you’re not exercising for over an hour at high intensity, you can skip the sports drinks, but not the water. For those who do not exercise or do so at a low to moderate intensity, sports drinks are merely another source of extra calories, sugar, and salt.
Dietary Reference Intakes For Sodium
The AI level for sodium for healthy adults between the ages of nineteen and fifty is 1,500 milligrams (Table 10.2 “Dietary reference intakes for sodium”). Table salt is approximately 40 percent sodium and 60 percent chloride. As a reference point, only ⅔ teaspoon of salt is needed in the diet to meet the AI for sodium. The AI considers the amount of sodium lost in sweat during recommended physical activity levels and additionally accounts for the sufficient intake of other nutrients, such as chloride. The Tolerable Upper Intake Level (UL) for sodium is 2,300 milligrams per day for adults (just over 1 teaspoon of salt contains the 2,300 milligrams of sodium recommended). The UL is considered appropriate for healthy individuals but not those with hypertension (high blood pressure). Many scientific studies demonstrate that reducing salt intake prevents hypertension, helps reduce blood pressure after hypertension is diagnosed, and reduces the risk for cardiovascular disease. People over fifty, African Americans, and those with chronic kidney disease or diabetes should consume no more than 1,500 milligrams of sodium per day.
| Age Group | Adequate Intake (mg/day) | Tolerable Upper Intake Level (mg/day) |
| Infants (0–6 months) | 120 | ND |
| Infants (6–12 months) | 370 | ND |
| Children (1–3 years) | 1,000 | 1,500 |
| Children (4–8 years) | 1,200 | 1,900 |
| Children (9–13 years) | 1,500 | 2,200 |
| Adolescents (14–18 years) | 1,500 | 2,300 |
| Adults (19–50 years) | 1,500 | 2,300 |
| Adults (50–70 years) | 1,300 | 2,300 |
| Adults (> 70 years) | 1,200 | 2,300 |
| ND = not determined | ||
| Data source: (“Dietary Reference Intakes,” 2004)[3] | ||
Dietary Sources of Sodium
Most sodium in the typical Canadian diet comes from processed and prepared foods. Manufacturers add salt to foods to improve texture and flavor, and also as a preservative. The amount of salt in similar food products varies widely. Some foods, such as meat, poultry, and dairy foods contain naturally occurring sodium. For example, one cup of low-fat milk contains 107 milligrams of sodium. Naturally occurring sodium accounts for less than 12 percent of dietary intake in a typical diet. For the sodium contents of various foods, see Table 10.3 “Sodium contents of selected foods”.
| Food Group | Serving Size | Sodium (mg) |
| Breads, all types | 1 oz. | 95–210 |
| Rice Chex cereal | 1 ¼ c. | 292 |
| Raisin Bran cereal | 1 c. | 362 |
| Frozen pizza, plain, cheese | 4 oz. | 450–1200 |
| Frozen vegetables, all types | ½ c. | 2–160 |
| Salad dressing, regular fat, all types | 2 Tbsp. | 110–505 |
| Salsa | 2 Tbsp. | 150–240 |
| Soup (tomato), reconstituted | 8 oz. | 700–1260 |
| Potato chips | 1 oz. (28.4 g) | 120–180 |
| Tortilla chips | 1 oz. (28.4 g) | 105–160 |
| Pork | 3 oz. | 59 |
| Chicken | (½ breast) | 69 |
| Chicken fast food dinner | 2243 | |
| Chicken noodle soup | 1 c. | 1107 |
| Dill pickle | 1 | 928 |
| Soy sauce | 1 Tbsp. | 1029 |
| Canned corn | 1 c. | 384 |
| Baked beans, canned | 1 c. | 856 |
| Hot dog | 1 | 639 |
| Burger, fast-food | 1 | 990 |
| Steak | 3 oz. | 55 |
| Canned tuna | 3 oz. | 384 |
| Fresh tuna | 3 oz. | 50 |
| Dry-roasted peanuts | 1 c. | 986 |
| American cheese | 1 oz. | 406 |
| Tap water | 8 oz. | 12 |
Sodium on the Nutrition Facts Panel
The Nutrition Facts panel displays the amount of sodium (in milligrams) per serving of the food in question (Figure 10.10 “Nutrition label” ). Food additives are often high in sodium. For example, monosodium glutamate (MSG) contains 12 percent sodium. Additionally, baking soda, baking powder, disodium phosphate, sodium alginate, and sodium nitrate or nitrite contain a significant proportion of sodium as well. When you see a food’s Nutrition Facts label, you can check the ingredients list to identify the source of the added sodium.
| Meaning | |
|---|---|
| Free of sodium or salt “free of sodium” “sodium-free” |
The food contains: (a) less than 5 mg of sodium per reference amount and serving of stated size; or (b) less than 5 mg of sodium or salt per serving of stated size, if the food is a prepackaged meal. |
| Low in sodium or salt “low in sodium” “low sodium” |
The food contains: (a) 140 mg or less of sodium per reference amount and serving of stated size and, if the reference amount is 30 g or 30 mL or less, per 50 g; or (b) 140 mg or less of sodium per 100 g, if the food is a prepackaged meal. |
| c) Reduced in sodium or salt “reduced in sodium” “reduced sodium” |
1) The food is processed, formulated, reformulated or otherwise modified so that it contains at least 25% less sodium
2) The similar reference food does not meet the conditions set out in column 2 of the subject “low in sodium or salt” set out in item b) of this table. |
| Lower in sodium or salt “lower in sodium” “less sodium” |
1) The food contains at least 25% less sodium
2) The reference food of the same food group does not meet the conditions set out in column 2 of the subject “low in sodium or salt” set out in item b) of this table. |
| No added sodium or salt “no added sodium” “without added sodium” |
1) The food contains no added salt, other sodium salts or ingredients that contain sodium that functionally substitute for added salt. 2) The similar reference food does not meet the conditions set out in column 2 of the subject “low in sodium or salt” set out in item b) of this table and contains added salt or other sodium salts. Note: Sodium or salt may not be an ingredient or a component of an ingredient of a product carrying the claim. |
| Lightly salted “lightly salted” “salted lightly” |
1) The food contains at least 50% less sodium added than the sodium added to the similar reference food. 2) The similar reference food does not meet the conditions set out in column 2 of the subject “low in sodium or salt” set out in item b) of this table. |
| Words to the effect that: the food is “for use in a sodium-restricted diet” | The food meets the conditions set out for one of the following claims: “free of sodium or salt” (item a) of this table), “low in sodium or salt” (item b) of this table), “reduced in sodium or salt” (item c) of this table), or “lower in sodium or salt” (item d) of this table). |
| Words to the effect that the food is “for special dietary use” with respect to the sodium (salt) content | The food meets the conditions set out for one of the following claims: “free of sodium or salt” (item a) of this table), “low in sodium or salt” (item b) of this table). |
| Data source: (“Specific Nutrient Claim Requirements,” n.d.)[4] | |
Tools for Change
To decrease your sodium intake, become a salt-savvy shopper by reading the labels and ingredient lists of processed foods and choosing those lower in salt. Even better, stay away from processed foods and control the seasoning of your foods. Eating a diet with less salty foods diminishes salt cravings so you may need to try a lower sodium diet for a week or two before you will be satisfied with the less salty food.
Salt Substitutes
For those with hypertension or those looking to decrease salt consumption, using a salt substitute for food preparation is one option. However, many salt substitutes still contain sodium, just in lesser amounts than table salt. Also, remember that most salt in the diet is not from table-salt use, but from processed foods. Salt substitutes often replace sodium with potassium. People with kidney disorders often have problems getting rid of excess potassium in their diet and are advised to avoid salt substitutes containing potassium. People with liver disorders should also avoid salt substitutes containing potassium because their treatment is often accompanied by potassium dysregulation. Table 10.5 “Salt substitutes” displays the sodium and potassium amounts in some salt substitutes.
| Product | Serving Size | Sodium (mg) | Potassium (mg) |
| Salt | 1 tsp. | 2,300 | 0 |
| Mrs. Dash | 1 tsp. | 0 | 40 |
| Spike (Salt-Free) | 1 tsp. | 0 | 96 |
| Veg-It | 1 tsp. | <65 | <65 |
| Accent Low-Sodium Seasoning | 1 tsp. | 600 | 0 |
| Salt Sense | 1 tsp. | 1,560 | 0 |
| Pleasoning Mini-Mini Salt | 1 tsp. | 440 | 0 |
| Morton Lite Salt | 1 tsp. | 1,100 | 1,500 |
| Estee Salt-It | 1 tsp. | 0 | 3,520 |
| Morton Nature’s Seasons | 1 tsp. | 1,300 | 2,800 |
| Morton Salt Substitute | 1 tsp. | 0 | 2,730 |
| No Salt | 1 tsp. | 5 | 2,500 |
| Nu-Salt | 1 tsp. | 0 | 529 |
| Data source: (“Health Facts,” 2011)[5] | |||
Alternative Seasonings
Table salt may seem an essential ingredient of good food, but others provide an alternative taste and zest to your foods. See Table 10.6 for a list of alternative food seasonings.
| Seasoning | Foods |
| Allspice | Lean ground meats, stews, tomatoes, peaches, applesauce, cranberry sauce, gravies, lean meat |
| Almond extract | Puddings, fruits |
| Caraway seeds | Lean meats, stews, soups, salads, breads, cabbage, asparagus, noodles |
| Chives | Salads, sauces, soups, lean-meat dishes, vegetables |
| Cider vinegar | Salads, vegetables, sauces |
| Cinnamon | Fruits, breads, pie crusts |
| Curry powder | Lean meats (especially lamb), veal, chicken, fish, tomatoes, tomato soup, mayonnaise, |
| Dill | fish sauces, soups, tomatoes, cabbages, carrots, cauliflower, green beans, cucumbers, potatoes, salads, macaroni, lamb |
| Garlic (not garlic salt) | Lean meats, fish, soups, salads, vegetables, tomatoes, potatoes |
| Ginger | Chicken, fruits |
| Lemon juice | Lean meats, fish, poultry, salads, vegetables |
| Mace | Hot breads, apples, fruit salads, carrots, cauliflower, squash, potatoes, veal, lamb |
| Mustard (dry) | lean ground meats, lean meats, chicken, fish, salads, asparagus, broccoli, Brussels sprouts, cabbage, mayonnaise, sauces |
| Nutmeg | Fruits, pie crust, lemonade, potatoes, chicken, fish, lean meatloaf, toast, veal, pudding |
| Onion powder | Lean meats, stews, vegetables, salads, soups |
| Paprika | Lean meats, fish, soups, salads, sauces, vegetables |
| Parsley | Lean meats, fish, soups, salads, sauces, vegetables |
| Peppermint extract | Puddings, fruits |
| Pimiento | Salads, vegetables, casserole dishes |
| Rosemary | Chicken, veal, lean meatloaf, lean beef, lean pork, sauces, stuffings, potatoes, peas, lima beans |
| Sage | Lean meats, stews, biscuits, tomatoes, green beans, fish, lima beans, onions, lean pork |
| Savory | Salads, lean pork, lean ground meats, soups, green beans, squash, tomatoes, lima beans, peas |
| Thyme | Lean meats (especially veal and lean pork), sauces, soups, onions, peas, tomatoes, salads |
| Turmeric | Lean meats, fish, sauces, rice |
| Data source: (“Shaking the Salt Habit,” 2012)[6] | |
Consuming Too Little Sodium
Consuming too much water in conjunction with not enough sodium, prolonged sweating, vomiting, and diarrhea can all result in hyponatremia, which is an abnormally low blood sodium level. Symptoms of hyponatremia include headaches, dizziness, fatigue, nausea, vomiting, and muscle cramps, and if left untreated, can result in seizures, coma, and death.
Consuming Too Much Sodium
Studies have established a relationship between sodium intake and blood pressure; reducing sodium intake reduces blood pressure, especially in people with hypertension. Some studies have shown that individuals with normal blood pressure benefit the least from sodium reduction.[7] However, others are not in agreement with this. For example, in a study conducted on middle-aged to elderly participants, researchers noted that a lower sodium intake significantly lowered blood pressure values when compared to a high-sodium diet after just one week; these reductions in blood pressure were independent of the participants’ hypertensive/normotensive status and antihypertensive medication use.[8]
From this, it can be suggested that low-sodium diets are effective in lowering blood pressure values among hypertensive and normotensive individuals.
On the opposite end of the spectrum, it’s often thought that high-sodium diets may significantly elevate blood pressure. However, one study suggested that high sodium diets had no significant effect on blood pressure[9], but within this study, participants on average consumed ~4.5 g, which far exceeds the RDA and those in the high sodium group increased the daily sodium intake by 1.1 g. This is not to say that high-sodium diets do not contribute to negative health outcomes. Instead, it simply suggests that our diets are often laden with sodium and increasing your sodium intake beyond a certain point results in little to no further increases in blood pressure. This is further supported by research studies that have consistently reported that once you adopt a low-sodium diet, reverting to a high-sodium diet results in significant elevations in your blood pressure.[10]
Genetic factors may modify the effect of sodium on blood pressure, and this salt sensitivity is discussed more in the hypertension section of the book. To summarize, some individuals maintain low blood pressure even though they consume levels associated with raised blood pressure.[11]
- Sawaka M, Burke L, Eichner E, Maughan R, Montain S, Stachenfeld N. Exercise and Fluid Replacement. Med Sci Sport Exerc. 2007 Feb;39(2):377–90. ↵
- Thompson J, Manore M, Vaughan L, Gottschall-Pass K, MacLellan D. The Science of Nutrition, Canadian Edition. Upper Saddle River, New Jersey, USA: Pearson Canada Inc; 2014. ↵
- Dietary Reference Intakes: Water, Potassium, Sodium, Chloride, and Sulfate. Institute of Medicine. http://www.iom.edu/Reports/2004/Dietary-Reference-Intakes-Water-Potassium-Sodium-Chloride-and-Sulfate.aspx. Updated February 11, 2004. Accessed September 22, 2017. ↵
- Specific Nutrient Content Claim Requirements, Government of Canada https://inspection.canada.ca/food-labels/labelling/industry/nutrient-content/specific-claim-requirements/eng/1627085614476/1627085788924#a9 ↵
- Health Facts for You: Guidelines for a Low Sodium Diet. University of Wisconsin Hospitals and Clinics Authority. http://www.uhs.wisc.edu/health-topics/nutrition-fitness-and-heart-health/documents/Sodium.pdf. Updated March 2011. Accessed September 22, 2017. ↵
- Shaking the Salt Habit. American Heart Association. http://www.heart.org/HEARTORG/Conditions/HighBloodPressure/PreventionTreatmentofHighBloodPressure/Shaking-the-Salt-Habit_UCM_303241_Article.jsp. Updated June 6, 2012. Accessed September 22, 2017. ↵
- Cook NR, He FJ, MacGregor GA, Graudal N. Sodium and health—concordance and controversy. BMJ. 2020 Jun 26;m2440. ↵
- Gupta, D. K., Lewis, C. E., Varady, K. A., Su, Y. R., Madhur, M. S., Lackland, D. T., Reis, J. P., Wang, T. J., Lloyd-Jones, D. M., & Allen, N. B. (2023). Effect of Dietary Sodium on Blood Pressure: A Crossover Trial. JAMA: Journal of the American Medical Association, 330(23), 2258–2266. https://doi.org/10.1001/jama.2023.23651. ↵
- Gupta, D. K., Lewis, C. E., Varady, K. A., Su, Y. R., Madhur, M. S., Lackland, D. T., Reis, J. P., Wang, T. J., Lloyd-Jones, D. M., & Allen, N. B. (2023). Effect of Dietary Sodium on Blood Pressure: A Crossover Trial. JAMA: Journal of the American Medical Association, 330(23), 2258–2266. https://doi.org/10.1001/jama.2023.23651. ↵
- Gupta, D. K., Lewis, C. E., Varady, K. A., Su, Y. R., Madhur, M. S., Lackland, D. T., Reis, J. P., Wang, T. J., Lloyd-Jones, D. M., & Allen, N. B. (2023). Effect of Dietary Sodium on Blood Pressure: A Crossover Trial. JAMA: Journal of the American Medical Association, 330(23), 2258–2266. https://doi.org/10.1001/jama.2023.23651. ↵
- Cook NR, He FJ, MacGregor GA, Graudal N. Sodium and health—concordance and controversy. BMJ. 2020 Jun 26;m2440. ↵
