As long as you eat enough food every day, it's unlikely you'll become deficient in sodium, even if you avoid heavily processed foods and salt (including sea salt). Small amounts of sodium occur naturally in vegetables, meat, seafood, milk, cheese and breads.
You can drive your blood levels of sodium down to dangerous levels if you drink too much water. This causes a condition called hyponatremia that can cause muscle cramps, nausea, vomiting, dizziness, and if not treated, can lead to shock and coma.
According to the Merck Manual, it would take six gallons of water on a regular daily basis to affect a healthy young adult. If you have certain heart, liver kidney problems, you may be at a greater risk of hyponatremia, and should speak to your doctor about how much water to drink every day.
What About Sweating?
You normally lose a little sodium every day when you sweat, but your diet provides enough sodium to replace the amount lost. It's possible to become deficient in sodium if you sweat too much, like when you over-exert yourself on a very hot day. You can prevent sodium loss by drinking sports drinks that contain electrolytes.
How Much Sodium Do I Need?
According to the United States Institute of Medicine, you need about 1,500 milligrams per day to replace what you normally lose. You can easily get that much by eating a healthy diet.
A cup of milk has around 140 milligrams of sodium, four ounces of beef has about 60 milligrams, and a large stalk of celery has about 50 milligrams. These are all considered low in sodium because they're at or below 140 milligrams per serving, but you can see how they'd still add up during the day.
Processed foods are high in sodium. It's common for people to eat in excess of 3,000 milligrams every day. If you don't have high blood pressure (or are at a high risk of getting high blood pressure), you can have up to 2,400 milligrams per day. The IOM sets 1,500 milligrams as the target for anyone with high blood pressure, over the age of fifty, and African-Americans of all ages.
Why Is Sodium Important?
There's so much written about cutting back on sodium that it can be difficult to remember that it's an essential nutrient. Sodium is an electrolyte, which means it helps keep your fluid levels in balance by working with water, potassium and chloride. You also need sodium for normal nerve and muscle function.
Gropper SS, Smith JL, Groff JL. "Advanced Nutrition and Human Metabolism." Sixth Edition. Belmont, CA. Wadsworth Pub Co. 2012.
Institute of Medicine of the National Academies. "Dietary Reference Intakes: Water, Potassium, Sodium, Chloride, and Sulfate." Accessed September 26, 2012. http://www.iom.edu/Reports/2004/Dietary-Reference-Intakes-Water-Potassium-Sodium-Chloride-and-Sulfate.aspx.
Lab Tests Online. "Sodium." Accessed September 26, 2012. http://labtestsonline.org/understanding/analytes/sodium/tab/test
The Merck Manual. "Overhydration." Accessed September 26, 2012. http://www.merckmanuals.com/home/hormonal_and_metabolic_disorders/water_balance/overhydration.html.
United States Department of Agriculture. "National Nutrient Database for Standard Reference Release 24." Accessed September 26, 2012. http://ndb.nal.usda.gov.