Table Salt, Sea Salt, and Iodine

Table of Contents

1. Salt Is Sodium Chloride, Whatever the Label Says
2. The Same Sodium the Renin System Responds To
3. Sea, Kosher, Pink and Table Salt: 97–99% NaCl
4. The Trace Minerals in Specialty Salts
5. By Weight vs. by Volume: Why a Teaspoon Differs
6. Salt Types Compared
7. Iodized Salt as an Iodine Source
8. Iodine When the Salt Is Not Iodized
9. Potassium-Based Salt Substitutes
10. Where Extra Salt Does Not Help
11. Why the Cause Is Sorted Out With a Blood Test
12. Key Research Papers
13. Connections
14. Featured Videos

Salt Is Sodium Chloride, Whatever the Label Says

Every culinary salt is mined from ancient underground deposits or evaporated from seawater or brine, and in both cases the crystal that forms is sodium chloride (NaCl): one sodium ion bound to one chloride ion. By weight, sodium makes up about 39% of sodium chloride and chloride the remaining 61%, so one gram of pure salt carries roughly 390 mg of sodium. That ratio is fixed by chemistry; it does not change with the colour, origin, harvesting method or price of the salt.

What varies between products is the small remainder: traces of moisture, other minerals carried over from the seawater or rock (magnesium, calcium, potassium, sulfate, iron oxides that tint pink salt), and, in table salt, deliberate additions — iodine in iodized salt and a small amount of anti-caking agent that keeps fine grains pouring freely.

For sodium purposes, then, the body does not distinguish between them. Once dissolved in food or in the gut, a sodium ion from sea salt is indistinguishable from a sodium ion from table salt, and it is absorbed, distributed and excreted in the same way.

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The Same Sodium the Renin System Responds To

The kidneys monitor the body’s sodium and fluid status continuously. When sodium intake falls and blood volume dips, specialised cells in the kidney release renin, which sets off the renin–angiotensin–aldosterone cascade: angiotensin II tightens blood vessels, and aldosterone signals the kidney to hold on to sodium (and with it, water) while letting potassium go. When sodium intake rises again, renin and aldosterone fall back. The sibling page on low sodium, the renin pathway and heart rhythm covers this loop in detail, and the aldosterone–renin ratio page describes how it is measured.

Table salt is the same sodium this system responds to. Where dietary sodium intake is genuinely too low — for example, in some people on very restricted diets, in heavy sweaters, or in conditions such as POTS where clinicians sometimes prescribe added salt — salting food raises sodium intake as effectively as any other sodium source. No specialty salt, mineral drink or supplement delivers sodium that the kidneys treat differently. (Sodium bicarbonate, the other common household sodium compound, is compared with table salt on the sibling page Baking Soda vs. Table Salt.)

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Sea, Kosher, Pink and Table Salt: 97–99% NaCl

Analyses of retail salts put the sodium chloride content of nearly every culinary type in a narrow band of roughly 97–99% by dry weight, with refined table salt at the top of that band (often above 99%) and unrefined sea salts and rock salts slightly lower, because they keep more moisture and more of the other minerals from their source.

• Table salt is mined or evaporated, then refined to nearly pure NaCl and ground into small, dense cubes. It is the type most often iodized, and it usually contains an anti-caking agent.
• Kosher salt takes its name from its use in the koshering of meat (drawing out surface blood), not from its chemistry. It comes as larger crystals — either hollow, pyramid-shaped flakes or compressed, flattened granules — and is usually not iodized.
• Sea salt is evaporated from seawater, sometimes minimally processed. Grain size ranges from fine to very coarse flakes. It is usually not iodized; the small amount of iodine in seawater is largely lost in evaporation and drying.
• Pink (rock) salt is mined from ancient salt deposits; the colour comes mainly from trace iron oxides. It is usually sold coarse or as a fine grind and is usually not iodized.
• Grey or “unrefined” sea salts are harvested damp and keep more moisture and clay-derived minerals, which lowers the NaCl percentage slightly by weight without changing the chemistry of the sodium itself.

Because the sodium fraction varies by only a few percentage points across all of these, a gram of any of them delivers close to the same amount of sodium — roughly 370–390 mg.

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The Trace Minerals in Specialty Salts

Specialty salts are often marketed on their trace-mineral content. The research describes those amounts as nutritionally negligible at normal intakes. The most detailed published analysis bought 31 pink salt samples (plus an iodized white table salt as a control) from retailers in two Australian cities and a regional town and measured 25 nutrient and non-nutrient minerals in each. Darker-coloured, flake-form and Himalayan-origin samples generally carried somewhat more minerals than paler ones (Fayet-Moore 2020).

The authors calculated that a person would need to eat more than 30 g of pink salt a day — about six teaspoons — before its minerals made a meaningful contribution to nutrient intake, and that such an amount would deliver a sodium load far above any recommended limit. They also found that one sample exceeded the national maximum contaminant level for lead set by the Australian and New Zealand food standards authority, a reminder that minimally processed salts carry whatever their source rock or water contained (Fayet-Moore 2020).

In practical terms, the potassium, magnesium and calcium in a pinch of specialty salt are tiny next to what ordinary foods supply: a single banana or a serving of leafy greens contains many times more potassium or magnesium than a day’s worth of any salt.

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By Weight vs. by Volume: Why a Teaspoon Differs

Gram for gram, the salt types are nearly identical in sodium. Spoon for spoon, they are not. The reason is crystal size and shape. Fine table-salt cubes pack tightly with very little air between them, so a level teaspoon holds about 6 g of salt. Large kosher flakes and coarse sea-salt crystals stack loosely, leaving air gaps, so a teaspoon of them weighs noticeably less — and therefore contains less sodium.

The commonly cited reference figure is that 1 teaspoon of table salt contains about 2,300 mg of sodium — which happens to equal the daily limit of 2,300 mg that the Dietary Guidelines for Americans set for adults. A teaspoon of a common flaked kosher salt, by contrast, carries roughly half that, and a teaspoon of a granulated kosher salt somewhere in between, according to the Nutrition Facts labels on those products.

This has two consequences that matter in everyday cooking:

• Recipes are not interchangeable by volume. A recipe written for flaked kosher salt that is made with fine table salt can end up with close to twice the sodium.
• “Less sodium” labelling on coarse salts reflects the spoon, not the salt. A product that lists lower sodium per ¼ teaspoon is usually delivering less salt per spoon, not a salt with less sodium in it. Used “to taste,” people tend to add more of a coarse salt to reach the same saltiness.

Pink and sea salts follow the same rule: a fine grind behaves much like table salt, while a coarse grind measures lighter by the spoon.

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Salt Types Compared

The figures below are approximate. The sodium-per-gram values follow from the NaCl content; the per-teaspoon values come from product Nutrition Facts labels (rounded) and vary with brand and grind.

The column that changes most is the last one — and it changes because of how the crystals stack in a spoon, not because any of these salts is a “low-sodium” salt.

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Iodized Salt as an Iodine Source

Iodine is the essential building block of the thyroid hormones T4 and T3. Adding it to salt is one of the most successful public-health measures on record: iodized salt was first sold in the United States in 1924, after goitre had been widespread in the Great Lakes, Appalachian and north-western “goitre belt” (Leung 2012). Worldwide, iodine deficiency remains the most common preventable cause of mental impairment, and salt iodization is described as the most effective way to control it (Zimmermann 2008).

Iodized table salt is a major iodine source for many people. In the United States it is labelled at 45 µg of iodine per gram, so a ¼ teaspoon supplies about 78 µg — roughly half the adult Recommended Dietary Allowance of 150 µg a day (NIH Office of Dietary Supplements). Three caveats from the research:

• Actual content varies. In 88 freshly opened US iodized-salt samples, 47 fell below the FDA-recommended iodine range and 6 were above it; iodine content also varied within a single container and was lost under humid storage, while light and dry heat had little effect (Dasgupta 2008).
• Iodization in the US is voluntary. An analysis of retail sales data identified 1,117 salt products; weighted by sales volume, about 53% of the salt sold at retail was iodized (Maalouf 2015).
• Most salt in processed and restaurant food is not iodized (NIH Office of Dietary Supplements) — and that is where most dietary sodium in the US comes from. Cutting back on the salt shaker therefore removes more iodine than sodium for many people, while eating plenty of packaged food supplies sodium with little iodine.

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Iodine When the Salt Is Not Iodized

Sea salt, kosher salt, pink salt and most other specialty salts are usually not iodized, and non-iodized sea salt provides virtually no iodine (NIH Office of Dietary Supplements). A switch from iodized table salt to one of these therefore removes that iodine source, unless iodine comes from elsewhere in the diet. The main other dietary sources reported by the NIH Office of Dietary Supplements are:

• Dairy — milk, yogurt and cheese; the iodine in milk depends on whether cows received iodine feed supplements and whether iodine-based sanitisers were used on cows and equipment. An analysis of 59 milk samples found 38–160 µg per cup; an ounce of cheddar supplies about 14 µg.
• Eggs — about 31 µg in a large hard-boiled egg.
• Seafood — ocean fish and shellfish; a 3-ounce serving of baked cod supplies about 146 µg and cooked oysters about 93 µg, while canned tuna supplies only about 7 µg.
• Seaweed — the richest source, but the most variable: content ranges from modest amounts in nori to very high levels in kelp, and some seaweed products can exceed the adult upper limit of 1,100 µg a day (see sea moss and iodine).

Iodine content in other foods depends heavily on local practice. A Boston-area survey found that most commercial breads contained little iodine, but a few varieties made with iodate dough conditioners carried more than 300 µg per slice; milk and infant formula were more consistent (Pearce 2004).

The groups for whom the research raises the most concern about a drop in iodine are pregnant and breastfeeding women (US RDA 220 and 290 µg a day), people who eat no dairy, eggs or seafood (for example, on a vegan diet), and people who rely entirely on non-iodized specialty salts. The iodine deficiency page covers the effects on the thyroid, including goitre and hypothyroidism; the iodine excess page covers the opposite problem.

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Potassium-Based Salt Substitutes

Salt substitutes are a different category from specialty salts: they replace part of the sodium chloride with potassium chloride, so they genuinely lower sodium per gram. In the large Salt Substitute and Stroke Study — about 21,000 people in 600 villages in rural China with a history of stroke, or aged 60 or older with high blood pressure — a substitute of roughly 75% sodium chloride and 25% potassium chloride lowered the rates of stroke, major cardiovascular events and death over about five years compared with regular salt, without a significant increase in high-potassium events (Neal 2021). The trial excluded people with serious kidney disease and those taking potassium-sparing medicines, and potassium-based substitutes are a recognised concern in those groups because their kidneys may not clear extra potassium.

Regulators are beginning to address these products directly; the FDA salt-substitutes rule page reports the US action on their use in standardized foods.

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Where Extra Salt Does Not Help

Low sodium intake and low sodium in the blood are not the same thing. Blood sodium (serum sodium, normally about 135–145 mmol/L) is a measure of concentration — how much sodium there is relative to water. Most cases of hyponatremia are caused by too much water being retained or taken in, not by too little salt being eaten (Sterns 2015). In several common situations, eating more salt may not fix the low reading and can be the wrong move:

• Excess water intake. Drinking far more fluid than the kidneys can excrete — in endurance events, in primary polydipsia, or on a “tea and toast” diet very low in solute — dilutes the blood. The problem is the water; restricting fluid is the usual correction.
• SIADH (syndrome of inappropriate antidiuresis). Here antidiuretic hormone is released even though the blood is already dilute, so the kidneys hold on to water while total body sodium is roughly normal. Extra sodium tends to be excreted in the urine while the water stays, and in some patients salt solutions can even lower the serum sodium further; fluid restriction and treatment of the underlying cause are the standard measures (Ellison and Berl 2007).
• Diuretics. Thiazide diuretics are among the most common causes of hyponatremia, particularly in older women; they impair the kidney’s ability to dilute urine. Management centres on the medicine itself, a decision that belongs with the prescriber (Spasovski 2014).
• Fluid-overload states. In heart failure, cirrhosis and advanced kidney disease the body already holds excess sodium and excess water; added salt worsens swelling and fluid build-up.

Only in true sodium and volume depletion — for example after heavy sweating, vomiting or diarrhoea — does replacing sodium address the cause directly. The sibling page on dizziness from low sodium sets out how hyponatremia differs from simple volume depletion.

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Why the Cause Is Sorted Out With a Blood Test

Because the treatment of low serum sodium depends entirely on its cause, clinical guidelines sort it out with testing rather than with self-adjusted salt intake. The European clinical practice guideline and later compilations of the US and European guidance describe the same sequence (Spasovski 2014; Hoorn and Zietse 2017):

1. Serum sodium, usually on a basic or comprehensive metabolic panel, confirms hyponatremia and its severity.
2. Serum osmolality separates true (hypotonic) hyponatremia from false readings caused by very high blood sugar or lipids.
3. Urine osmolality shows whether antidiuretic hormone is active (concentrated urine) or the kidneys are excreting water freely (dilute urine, typical of excess intake).
4. Urine sodium, together with an assessment of fluid status, helps distinguish salt and volume depletion from SIADH, diuretic effects and fluid-overload states.

Speed matters too. When chronic hyponatremia is corrected too quickly, the brain can be injured by osmotic demyelination, which is why guidelines set limits on how fast serum sodium is raised in the first 24 hours (Sterns 2015; Spasovski 2014). Clinical sources describe this as one of the reasons persistent low sodium readings are handled as a medical question rather than adjusted with the salt shaker alone. Further detail sits on the hyponatremia hub.

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Key Research Papers

1. Fayet-Moore F, Wibisono C, Carr P, et al. (2020). An Analysis of the Mineral Composition of Pink Salt Available in Australia. Foods;9(10):1490. — DOI: 10.3390/foods9101490. — doi:10.3390/foods9101490
2. Dasgupta PK, Liu Y, Dyke JV (2008). Iodine nutrition: iodine content of iodized salt in the United States. Environmental Science & Technology;42(4):1315-1323. — DOI: 10.1021/es0719071. — doi:10.1021/es0719071
3. Maalouf J, Barron J, Gunn JP, et al. (2015). Iodized Salt Sales in the United States. Nutrients;7(3):1691-1695. — DOI: 10.3390/nu7031691. — doi:10.3390/nu7031691
4. Leung AM, Braverman LE, Pearce EN (2012). History of U.S. Iodine Fortification and Supplementation. Nutrients;4(11):1740-1746. — DOI: 10.3390/nu4111740. — doi:10.3390/nu4111740
5. Zimmermann MB, Jooste PL, Pandav CS (2008). Iodine-deficiency disorders. The Lancet;372(9645):1251-1262. — DOI: 10.1016/S0140-6736(08)61005-3. — doi:10.1016/S0140-6736(08)61005-3
6. Pearce EN, Pino S, He X, et al. (2004). Sources of Dietary Iodine: Bread, Cows’ Milk, and Infant Formula in the Boston Area. Journal of Clinical Endocrinology & Metabolism;89(7):3421-3424. — DOI: 10.1210/jc.2003-032002. — doi:10.1210/jc.2003-032002
7. Neal B, Wu Y, Feng X, et al. (2021). Effect of Salt Substitution on Cardiovascular Events and Death. New England Journal of Medicine;385(12):1067-1077. — DOI: 10.1056/NEJMoa2105675. — doi:10.1056/NEJMoa2105675
8. Ellison DH, Berl T (2007). The Syndrome of Inappropriate Antidiuresis. New England Journal of Medicine;356(20):2064-2072. — DOI: 10.1056/NEJMcp066837. — doi:10.1056/NEJMcp066837
9. Sterns RH (2015). Disorders of Plasma Sodium — Causes, Consequences, and Correction. New England Journal of Medicine;372(1):55-65. — DOI: 10.1056/NEJMra1404489. — doi:10.1056/NEJMra1404489
10. Spasovski G, Vanholder R, Allolio B, et al. (2014). Clinical practice guideline on diagnosis and treatment of hyponatraemia. European Journal of Endocrinology;170(3):G1-G47. — DOI: 10.1530/EJE-13-1020. — doi:10.1530/EJE-13-1020
11. Hoorn EJ, Zietse R (2017). Diagnosis and Treatment of Hyponatremia: Compilation of the Guidelines. Journal of the American Society of Nephrology;28(5):1340-1349. — DOI: 10.1681/ASN.2016101139. — doi:10.1681/ASN.2016101139

PubMed Topic Searches

1. PubMed: Mineral composition of sea and specialty salts
2. PubMed: Iodine content of iodized salt
3. PubMed: Dietary iodine sources beyond salt
4. PubMed: Potassium chloride salt substitutes
5. PubMed: Hyponatremia causes and diagnostic work-up

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Connections

• Sodium Overview
• Dizziness from Low Sodium
• Low Sodium, Renin, and Heart Rhythm
• Baking Soda vs. Table Salt
• Hyponatremia Symptom Hub
• Hypernatremia and Salt Excess
• Iodine
• Iodine Deficiency
• Hypothyroidism
• Chloride
• Potassium
• FDA Rule on Salt Substitutes

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