Calcium

How much calcium do you need?

The Recommended Dietary Allowance (RDA) for calcium for adults has been set at 1,000 mg (1 g) per day ^[1]. The average calcium intake in Americans (data from 2003-2006) is about 700-1,200 mg/day and is lower in women than in men ^[6].

Chart 1. Recommended Dietary Allowance (RDA) for calcium
AGE	RDA (mg/day)
Infants 0-6 months	200 (Adequate Intake)*
Infants 7-12 months	260 (Adequate Intake)
Children 1-3 years	700
Children 4-8 years	1,000
9-18 years, including pregnant and breastfeeding women	1,300
Adults 19-70 years, including pregnant and breastfeeding women	1,000
Adults 71+ years	1,200

Chart 1. source: The Food and Nutrition Board of the U.S. Institute of Medicine (IOM) ^[1] *Breast milk of healthy mothers should provide enough calcium for exclusively breastfed infants 0-6 months of age ^[1,3].

Foods Rich in Calcium

Common foods rich in calcium include dairy products, calcium-fortified foods, fish with edible bones, almond milk, radishes and certain mineral waters.

Picture 1. Non-dairy foods high in calcium

Chart 2. List of foods high in calcium
DAIRY	CALCIUM (mg)
Cheese, American pasteurized	700-1,000
Cheese, Gruyere, romano, Swiss  (2.5 oz, 70 g)	700-750
Cheese, blue, brick, caraway, cheddar, colby, edam, gouda, gout, Mexican blend, monterey, muenster, provolone, Roquefort, Swiss-processed, tilsit (2.5 oz, 70 g)	400-600
Milk, sheep (1 cup, 237 mL)	470
Yogurt, plain (6 oz, 170 g)	350
Mozzarella (2.5 oz, 70 g)	350-670
Cheese, feta (2.5 oz, 70 g)	350
Milk cow/goat, nonfat, skim, whole (1 cup, 237 mL)	300
Cheese, brie, camembert, Ricotta (2.5 oz, 70 g)	150-300
Whey, sweet, powder (1 oz, 28 g)	220
Cheese, cottage, cream, neufchatel (2.5 oz, 70 g)	60
NON-DAIRY	CALCIUM (mg)
Meat, Fish
Sardines, Atlantic, with bones (1 can, 92 g)	350
Canned mackerel and salmon (pink, chum, sockeye) with bones (1 can, 92 g)	200-250
Crabs, cuttlefish, shrimps, canned (3 oz, 85 g)	100-150
Carp, burbot, herring, trout (3 oz, 85 g)	50-80
Cereals
Granola bar (60 g)	200
Bread, wheat, white or whole-grain (2 small slices, 60 g)	40-80
Vegetables, Beans
Radishes, oriental, dried (1/2 cup, 60 g)	360
Lambsquarters (1/2 cup, 90 g)	230
Taro (1 cup, 137 g)	200
Blackstrap molasses (1 tbsp, 20 g) [42]	170
Amaranth leaves, collards, turnip greens (1/2 cup, ~80 g)	120-135
Soybeans, green, boiled (1/2 cup, 90 g)	130
Cowpeas (1/2 cup, 100 g)	100
Tempeh (1/2 cup, 80 g)	90
Chinese cabbage, bok choi; kale, Scotch; okra (1/2 cup, ~80 g)	70-85
Carrots, boiled (1/2 cup, 75 g)	50
Nuts, Seeds
Almond milk (1 cup, 237 mL)	450
Chia seeds (1 oz, 28 g)	180
Chestnuts, Japanese, dried (1 cup, 150 g)	110
Sesame seeds (1 tbsp, 9 g)	90
Almonds (1 oz, 28 g)	80
Coconut water (1 cup, 237 mL)	60
Fruits
Figs, dried (1/2 cup, 75 g)	120
Kiwi fruit, orange, prickly pear (1 fruit or 1 cup)	70
Prunes (1/2 cup, 60 g)	50
Water
Mineral water (1 cup, 237 mL) [4]	0-130
Tap water (1 cup, 137 mL) [5]	0-35
EXAMPLES OF CALCIUM-FORTIFIED FOODS AND JUICES	CALCIUM (mg)
Cereals, ready-to-eat (1 cup, prepared with water)	100-1,000
Tofu with calcium sulfate (1 block, 80 g)	550
Formulated bar (55 g)	530
Milk (1 cup, 237 mL)	500
Cornmeal, self-rising (1 cup, 237 mL)	500
Bread, wheat, white, fortified (2 small slices, 60 g)	400
Orange juice (1 cup, 237 mL)	350
Fruit or vegetable juice, soy milk, rice drink (1 cup, 237 mL)	200-350
Cocoa powder (1 packet, 15 g)	200
English muffin with calcium propionate (57 g)	100

Chart 2. source: US Department of Agriculture (USDA.gov) ^[3] 

Can consuming too much calcium be bad for you?

The Institute of Medicine in the U.S. has set the Tolerable Upper Intake Level (UL) for calcium–the intake (from foods and supplements) unlikely to cause adverse effects in most healthy individuals 1 year or more of age–at 2,000-3,000 mg/day ^[1].

Men: Prostate Cancer

In several, but not all studies, high calcium intake (>1,000 mg/day) from either foods or supplements, and high dairy intake were associated with increased risk of prostate cancer ^[1,50]. Until more is known, Linus Pauling Institute in the U.S. recommends men to limit calcium intake to 1,000-1,2000 mg/day ^[1].

In one 2013 systematic review, researchers have found no convincing association between high calcium intake and other types of cancer (breast, lung, colorectal, endometrial) ^[15].

Coronary Heart Disease and Heart Attack

Results of studies of calcium intake on heart disease are controversial. In one study in women, high calcium intake (>1,400 mg/day) was associated with increased and in another study with decreased mortality due to heart disease ^[6], but one 2012 review of studies has found no association between calcium intake and coronary heart disease ^[59].

A Low-Calcium Diet

If you have a chronic kidney disease and tend to have elevated blood calcium levels, your doctor may recommend you to decrease calcium intake by eating more low-calcium foods and limit, but not necessary completely avoid, calcium-rich foods.

Low-calcium diet is NOT recommended to individuals with increased risk of calcium kidney stones ^[44,47].

Chart 4. Low-Calcium and Calcium-Free Foods
FOOD	CALCIUM (mg)
Kale, squash, winter (1/2 cup, 65 g)	45
Legumes: beans, lentils, peas (1/2 cup)	20-35
Broccoli (1/2 cup, 40 g)	30
Nuts: hazelnuts, macadamia, peanuts, pistachios, walnuts (1 oz, 28 g)	20-30
Meats: beef, chicken, lamb, pork, turkey, veal (3 oz, 85 g)	10-30
Fruits: apple, apricot, banana, blackberries, currants, cherries, elderberries, grapes, mango, peach, pear, pineapple, raspberries, strawberries (1 serving = berries: 1/2 cup, other: 1 cup or 1 fruit)	10-30
Potato, sweet potato, yam (1 cup, 160 g)	10-30
Sunflower seeds (1 oz, 28 g)	25
Egg (50 g)	25
Rice, white or brown, regular or parboiled; pasta: macaroni, spaghetti (1 cup, 150 g)	20
Tilefish, mackerel without bones (3 oz, 85 g), oyster, tuna (1 can, 92 g)	5-20
Bulgur, buckwheat, couscous, millet (1 cup, 170 g)	5-20
Tomato  (150 g), lettuce (1 cup), lemon (60 g), raisins (1 oz, 28 g)	15
Butter, coconut meat, honey, jam, margarine, oils, table sugar, vinegar (1 tbsp, 15-20 g), cornmeal, cornflakes, popcorn, distilled alcohol beverages, sausages, tea (ice, green, herbal, black) (1 serving)	0-5

Chart 4. source: US Department of Agriculture (USDA.gov) ^[3] 

Calcium Absorption and Excretion

Most of calcium is absorbed in the small intestine ^[6,65]. Oxalic acid (oxalate) found in spinach and rhubarb, and phytic acid (phytate) in dried beans and wheat bran inhibit calcium absorption, so these foods are not good sources of calcium ^[1]. Calcium from kale ^[60] and soybeans ^[63] is absorbed well. Most of calcium absorbed in excess of body needs is excreted with the urine ^[65]. Only small amounts of calcium are lost with sweat ^[64].

Normal Blood Calcium Levels Range

Normal blood calcium level range for adults is 8.6-10.2 mg/dL or 2.15-2.55 mmol/L ^[7].

Calcium Supplements

Types of Oral Calcium Supplements Without Prescription (Over-The-Counter)

• Calcium carbonate can be used as a calcium supplement or antacid.
  • “Coral calcium” or “marine calcium” supplements are derived from coral reefs and contain calcium carbonate and magnesium. In one small study in Japan, coral calcium carbonate was better absorbed than regular calcium carbonate ^[39], but there is no scientific evidence about its superiority over other calcium supplements.
  • “Bio-calcium” obtained from pearl shells contains calcium carbonate, which is, according to few studies, no more effective than calcium carbonate from other sources ^[41].
  • “Rock calcium” is a general term for inorganic calcium derived from limestone. Calcium carbonate and citrate are examples of rock calcium.
• Calcium citrate and citrate malate are appropriate for individuals with low gastric acid and increased risk of kidney stones.
• Calcium magnesium citrate is a calcium and magnesium supplement.
• Calcium lactate and gluconate are highly soluble but bulky, so they are mostly used as powders for solutions.
• Calcium phosphate is usually available in combination with vitamin D3.
• Calcium oxide (“lime”) and hydroxide (“slaked lime”) are sometimes used in multivitamin/mineral supplements and rarely, for example in Japan, as individual supplements, which are produced from oyster shells. They are more alkaline than other calcium supplements.
• In calcium orotate, calcium is combined with orothic acid, in calcium D-glucarate with glucaric acid, in calcium osporotate with aspartic, orothic and citric acid, in calcium amino acid chelates with hydrolyzed vegetable protein and in calcium AEP with amino ethanol phosphate. These supplements are often advertised to have greater bioavailability, but they have not been proven to be more effective than other calcium supplements.
• Calcium hydroxiapatite is derived from bovine bones.
• References: ^[6]

Available oral forms: tablets, capsules, chews, powder and liquids.

Chart 5. Calcium carbonate vs calcium citrate
PROPERTIES	CALCIUM CARBONATE	CALCIUM CITRATE
Uses	Calcium supplement, antacid (tums)	Calcium supplement
Amount of elemental calcium	40% (500 mg calcium carbonate contains 200 mg Ca)	21% (500 mg calcium citrate contains 105 mg Ca)
Recommended intake	With foods	With or without foods
Absorption in low gastric acid (achlorhydria, hypochlorhydria)	Poor	Good
Short-term side effects	Constipation, bloating	Less side effects than calcium carbonate
Risk of kidney stones with long-term use	Possibly	No

Chart 5. sources: ^[6,34,35]

Calcium Injections

In severe hypocalcemia, your doctor can give you an injection of calcium gluconate or chloride into a vein. These two supplements can be also used as antidotes to prevent adverse effects of hyperkalemia on the heart muscle but not to treat hyperkalemia itself ^[40].

Dosage

To treat calcium deficiency, a typical dose is 1 gram (1,000 mg) of elemental calcium per day ^[6]. It is your doctor who can prescribe the dose appropriate for you.

To know how much calcium you get from supplements you should check milligrams of elemental calcium, not milligrams of the the whole calcium compound.

Chart 6. Elemental Calcium
CALCIUM SUPPLEMENT	ELEMENTAL CALCIUM (mg of calcium in a 500 mg pill)
Ca oxide	71% (355 mg)
Ca hydroxide	54% (270 mg)
Ca carbonate	40% (200 mg)
Ca phosphate, tribasic	38% (190 mg)
Ca chloride	27.2% (136 mg)
Ca acetate	25.3% (126.5 mg)
Ca phosphate, dibasic	23% (115 mg)
Ca citrate	21% (105 mg)
Microcrystalline hydroxyapatite  (MH)	20% (100 mg)
Calcium chelates: orotate, aspartate	(about 100 mg)
Ca lactate	13% (65 mg)
Ca gluconate	9.3% (46.5 mg)
Ca gluceptate	8.2% (41 mg)
Ca glubionate	6.5% (32.5 mg)

Chart 6. source: Globalrph.com ⁽⁵⁴⁾, producers

Absorption and Bioavailability of Supplemental Calcium

Calcium is optimally absorbed when taken in doses up to 500 mg elemental calcium at once ^[6]. You can divide larger doses in half for better absorption.

Different calcium supplements are probably absorbed equally well and have about the same bioavailability. Unlike other supplements, calcium citrate and calcium citrate malate are absorbed well on an empty stomach and in low gastric acid (achlorhydria, hypochlorhydria) ^[6]. Calcium phosphate is less well absorbed, because phosphate binds to calcium in the gut and inhibits its absorption ^[26].

There is INSUFFICIENT EVIDENCE about calcium supplements effectiveness for preventing colorectal, prostate or other cancer, dental caries (tooth decay) ^[37,38], heart disease, high blood pressure ^[49], high blood pressure in pregnancy (pre-eclampsia), Lyme disease, metabolic syndrome, osteoporosis (in individuals who do not already have osteoporosis) ^[25], pregnancy-related leg cramps, diabetes, premenstrual syndrome (PMS), seizures, stroke or for promoting weight loss. Other references: ^[16,45,46].

Calcium supplements are POSSIBLY INEFFECTIVE for preventing breast cancer in postmenopausal women ^[16].

Calcium Supplements Safety: Side Effects, Toxicity

The Upper Tolerable Intake Limit (UL) for calcium–the intake unlikely to cause side effects in most healthy people–is: for 0-6 months: 1,000 mg/day; for 7-12 months: 1,500 mg/day; for 1-8 years: 2,500 mg/day; for 9-18 years: 3,000 mg/day; for 19-50 years: 2,500 mg/day and for 51 years and older: 2,000 mg/day ^[1].

Side effects of calcium supplements include constipation and bloating ^[6]. Injection of calcium chloride can irritate the veins or muscles ^[55].

Certain calcium supplements derived from bone meal, dolomite or oyster shells contain small amounts of lead, but calcium inhibits lead absorption in the gut, so the actual harm of lead is probably lower than the benefit from calcium supplements ^[1,29].

During Pregnancy

According to the U.S. Food and Drug Administration (FDA), pregnancy categories for calcium supplements are:

• “Not classified” for calcium carbonate, glubionate, phosphate
• Category C, which means harmful effects for the babies have been not proven but can not be excluded due to lack of human trials: calcium acetate, citrate, chloride, gluconate, lactate
• Source: Drugs.com: 17

Calcium-Nutrients Interactions

• Oxalate in spinach, rhubarb, beet greens, Swiss chard and beans can decrease calcium absorption from these foods, but not likely from other foods ^[6,19]. On the other hand, calcium reduces absorption of oxalate thus possibly reducing the risk of calcium-oxalate kidney stones.
• Phytates in seeds, nuts and wheat bran can decrease calcium absorption from these and other foods ^[20].

Frequently Asked Questions

1. Do vegans need to take calcium supplements?

Not necessary. Bread and calcium-enriched foods are good sources of calcium.

2. Which calcium supplements are vegan?

Most calcium supplements are vegan. Calcium lactate (E327) is usually derived from non-animal sources and only occasionally from whey, so it is “typically vegan.” Non-vegan supplements are calcium caseinate, stearate and hydroxyapatite, and supplements derived from bone meal, bone flour and shellfish shells ^[32].

3. Does caffeine causes calcium deficiency?

Caffeine slightly decreases calcium absorption but it is not clear if this has any importance for health ^[6,16,22,24].