Foods rich in calcium, potassium and iodine

Three minerals, three roles

Calcium, potassium and iodine have little in common, except that they are found in very different foods. Thecalciumis the main constituent of bones and teeth. Thepotassiumis involved in the functioning of cells, muscles and nerves. Theiodineis used to produce thyroid hormones. This article lists the main dietary sources of each, with data from the ANSES Ciqual table, and recalls the official guidelines. It does not replace the advice of a doctor or dietitian.

Reference intakes for an adult

The values below are taken from the ANSES opinion of March 2021 on nutrient reference values for vitamins and minerals, and from its 2018 opinion on iodine.

• Calcium: 950 mg per day for adults aged 25 and over, 1 000 mg for those aged 18 to 24. The upper safe limit, which applies to total intake, is 2 500 mg per day.
• Potassium: 3 500 mg per day for adults (adequate intake).
• Iodine: 150 µg per day for adults (adequate intake), 200 µg for pregnant or breastfeeding women. The upper safe limit, as set by EFSA, is 600 µg per day.

These guidelines apply to the general adult population. Requirements vary according to age, pregnancy or certain medical conditions. See alsoNutrition for seniors.

Where to find calcium?

Ciqual 2020 values, in mg per 100 g of food as consumed:

• Hard cheeses: Comté 993 mg, Emmental 898 mg. Camembert contains 449 mg, but these cheeses are also high in fat and salt.
• Plain fromage blanc: approximately 130 mg (130 mg for 3% fat, 134 mg for 0% fat).Plain yoghurt: 127 mg.
• Cow's milk: 117 mg for whole pasteurised milk and UHT semi-skimmed milk, 119 mg for pasteurised semi-skimmed milk.
• Canned sardines, drained: 333 mg in oil, 798 mg in olive oil. The difference is large: it depends on the presence of bones, which are eaten. Boneless fillets drop to 108 mg.
• Sesame seeds: 962 mg for whole seeds, 284 mg for sesame puree (tahini). The quantities consumed are small.
• Almonds with skin: 260 mg.
• Curly kaleraw: 185 mg, cooked: 72 mg.
• Cooked white beans: 120 mg.Cooked broccoli: 43 mg.
• Pre-packaged plain tofu: 100 mg. The content varies depending on the coagulant used: check the label, tofu prepared with calcium salt contains more.

Themineral waterscan also contribute to this. In the Ciqual table, most still or sparkling waters contain between 1 and 35 mg of calcium per 100 g, but highly mineralised waters go higher: 54.9 mg per 100 g for Hépar, 46.8 mg for Contrex, or about 550 and 470 mg per litre. Tap water averages 7.1 mg per 100 g. The composition varies from one water to another and is listed on the label.

Doing without dairy products

Plant-based drinks contain almost no calcium naturally: 12 mg per 100 g of unfortified plain soy drink, 1 mg for plain oat drink. Fortified versions come close: 98 mg for calcium-fortified plain soy, 54 mg for fortified sweetened almond. We therefore remain below the calcium content of cow's milk (117 mg). The mention "fortified with calcium" counts, and the list of ingredients indicates the added calcium salt. For a detailed comparison, seeCow's milk vs plant-based milk.

Without dairy products, other minerals also require attention, seeFoods rich in iron, zinc and magnesium.

Where to find potassium?

Potassium is mainly found in minimally processed plants. Ciqual 2020 values, in mg per 100 g:

• Cooked red beans: 300 mg.Cooked white beans: 260 mg.Cooked lentils: 222 mg.Cooked chickpeas: 170 mg.
• Raw spinach: 504 mg. Cooked in water: 160 mg, some of the potassium passes into the cooking water.
• Avocado: 430 mg.Banana: 320 mg.
• Potatoes: 363 mg boiled, 391 mg roasted in the oven without skin.
• Dried plums: 610 mg.
• Semi-skimmed UHT milk: 167 mg.

A 150 g portion of boiled potatoes provides about 545 mg, which is about 16% of the reference value of 3,500 mg. This reference is covered by a variety of vegetables, fruits and legumes rather than by a single food.Warning: in case of kidney failure or treatment that alters potassium in the blood, the doctor's opinion takes precedence over any general guideline.

Where can iodine be found?

Iodine is present in seafood, eggs, dairy products and iodised salt. Ciqual values 2020, in µg per 100 g:

• Smoked haddock: 255 µg.Raw cod: 101 µg (110 to 130 µg when cooked).
• Boiled mussels: 106 µg.Cooked shrimp(average Ciqual value): 260 µg.
• Hard-boiled egg: 49.7 µg, most of which is in the yolk (175 µg per 100 g of raw yolk).
• Cottage cheese, yoghurt, milk: from 10 to 29 µg depending on the product (pasteurised semi-skimmed milk 17.9 µg).
• Raw farmed salmon: 8.2 µg.Canned tuna in natural juices: 16 µg. Fatty fish are therefore less rich in iodine than lean fish.
• Iodised white table salt: 1,860 µg per 100 g, or about 19 µg per gram of salt. Non-iodised salt is at 1.8 µg per 100 g.

Iodised salt is a simple way to provide iodine, but it should not encourage people to add more salt: official recommendations aim to limit salt. To detect the salt hidden in products, seeHidden sugar and salt: where are they hiding?.

Seaweed: beware of excess iodine

Dried seaweed is the most iodine-rich food. The Ciqual table gives, for example, 5,100 µg per 100 g of dried nori, or 51 µg per gram, and 19,100 µg per 100 g of wakame. Kombu is on another level: 486,000 µg per 100 g of dried Breton kombu, or about 4,860 µg per gram, more than eight times the upper safety limit of 600 µg per day for a single gram.

In its 2018 opinion, ANSESadvises against the consumption of foods or supplements containing algaeby people with thyroid dysfunction, heart disease or kidney failure, those undergoing treatment containing iodine or lithium, and pregnant or breastfeeding women without medical advice. It recommends that regular consumers prefer products with a moderate iodine content, such as brine-cured or canned products, and specifies that algae are not relevant for correcting an iodine deficiency.

Supplements: caution is advised

The above guidelines apply to the entire diet. Safety limits (2,500 mg of calcium, 600 µg of iodine per day) also include supplements and fortified foods or water. For iodine, ANSES notes that the maximum dose set for dietary supplements is 150 µg per day. In case of thyroid, kidney or bone disorders, pregnancy or treatment, supplementation should be decided with a doctor or pharmacist, never alone.

Read the label

• For a plant-based drink, look for the words "enriched with calcium" and calcium salt in the list of ingredients: without them, the drink provides almost nothing.
• For salt, look for the words "iodised salt" or "iodised" in the ingredients.
• For seaweed, check the iodine content if it is indicated and follow the manufacturer's warnings.
• For mineral water, the calcium content is listed on the label: compare brands.

For more information, seeFoods rich in vitamins C and D and omega-3, because vitamin D plays a role in the use of calcium.

Sources

• ANSES - Nutritional reference values for vitamins and minerals, opinion and report (March 2021)
• ANSES - Opinion on the risk of excessive iodine intake due to seaweed consumption (25 June 2018)
• ANSES - Ciqual 2020 nutritional composition table (Zenodo copy)
• EFSA - Dietary Reference Values for nutrients