What is calcium?
Calcium is an essential mineral that is mainly found in the teeth and bones. It is the most abundant mineral in the body and accounts for 1-2% of adult body weight (1).
What does calcium do in the body?
Calcium is the foundation of bones and teeth, providing strength and stability, while also playing a vital role in muscle contraction, nerve transmission, and blood clotting.
Bone development
Calcium plays a crucial role in bone formation by combining with phosphate to create hydroxyapatite, the mineralized matrix that gives bones and teeth their hardness and strength (2).
It is also involved in bone remodeling, a process in which old bone tissue is broken down and replaced. This helps maintain bone strength and allows for adaptive changes to bone structure (3).
Muscle contraction
Calcium is needed for the proper functioning of muscles because it regulates the interaction between actin and myosin, the proteins responsible for muscle contraction (4).
When a muscle receives a nerve signal, calcium ions are released from the sarcoplasmic reticulum into the muscle fibers, where they bind to troponin, a regulatory protein.
This binding causes troponin to expose myosin-binding sites on actin, which allows myosin to pull on actin and results in a muscle contraction that continues until calcium is reabsorbed.
Blood clotting
Calcium is integral to the coagulation cascade, acting as a key cofactor in several stages of the blood clotting process and directly functioning as clotting factor IV (5, 6).
Calcium is essential for the activation of clotting factors II, VII, IX, and X, and it facilitates the conversion of prothrombin to thrombin, which forms the clot’s mesh-like structure.
Additionally, calcium supports platelet aggregation, allowing platelets to stick together and to the damaged blood vessel, which is vital for proper clot formation.
Nerve transmission
Calcium is necessary for nerve transmission. When an action potential (nerve signal) reaches the end of a neuron, it triggers the opening of voltage-gated calcium channels (7).
This causes calcium ions to flow into the neuron, prompting synaptic vesicles filled with neurotransmitters to merge with the cell membrane and release their contents at the synaptic cleft.
These neurotransmitters then bind to receptors on the adjacent neuron, continuing the transmission of the nerve signal.
How is calcium digested and absorbed?
Calcium is absorbed primarily in the small intestine via both active and passive transport. About 30% of calcium from foods and supplements is absorbed, but this varies depending on the form.
Digestion
Most dietary calcium is bound to other substances, such as oxalic acid, phytic acid, and various proteins. In order to be absorbed, it must be broken down into ionized (free) calcium (8).
This process occurs in the stomach, where hydrochloric acid breaks down these complexes, releasing calcium ions which can then be absorbed in the intestines.
Location of absorption
Calcium is absorbed throughout the intestinal tract, with more than 90% of absorption occurring in the small intestine (8).
Modes of transport
Calcium is absorbed via the following modes of transport (9):
- Transcellular (through cells) transport is the main mode of transport when calcium intake is low and takes place primarily in the duodenum. It is regulated by calcitriol (the active form of vitamin D).
- Paracellular (between cells) transport is the main mode of transport when calcium intake is high and takes place primarily in the duodenum, jejunum, and ileum.
Amount absorbed
On average, about 30% of the calcium found in foods is absorbed. However, absorption rates vary widely depending on the type of food (9).
For example, only about 5% of the calcium from spinach is absorbed, compared to 30% from dairy products, 40% from fortified orange juice, and 50% from broccoli, bok choy, and kale (8).
Absorption of supplemental calcium varies depending on the form and whether it is taken with or without food. Generally though, around 30-40% of the calcium in supplements is absorbed.
Impact of other food components
The following food components may decrease calcium absorption:
- Alcohol reduces calcium absorption, but is unlikely to have an impact on overall calcium status unless consumed in excess (10).
- Caffeine slightly decreases calcium absorption. It is estimated that this can be offset by increasing calcium intake by 40 mg for every 6-ounce serving of caffeinated coffee (11, 12).
- Oxalic acid (also called oxalate), found in dark leafy greens and other plants, can bind to calcium and reduce its absorption to as little as 5% (in spinach) (8, 13).
- Phytic acid (also called phytate) is found in the outer layers of grains, nuts, seeds, and legumes. It reduces calcium absorption by binding to it.
The following food components may increase calcium absorption:
- Protein stimulates the release of hydrochloric acid in the stomach, which helps to release free calcium from food, increasing its absorption (9).
- Vitamin D enhances calcium absorption by increasing the production of proteins in the small intestine that facilitate calcium transport into the bloodstream (9).
How is calcium transported and stored?
On average, the (adult) human body contains between 1,000 and 1,500 grams of calcium, around 99% of which is stored in bones and teeth as calcium hydroxyapatite (5, 8)
Only 1% of total body calcium is found in the blood (serum), where it exists in 3 different forms (5):
- Ionized (free) (50%)
- Bound to protein (mainly albumin) (40%)
- Bound to other molecules (such as citrate, lactate, or bicarbonate) (10%)
Serum calcium levels are tightly regulated by parathyroid hormone (PTH), calcitriol (vitamin D3), and calcitonin (4).
How is calcium excreted?
Excess calcium is primarily excreted via the kidneys (urine), but losses can also occur through the intestines (feces) and skin (sweat).
Intestines
On average, 70% of dietary calcium goes unabsorbed and is excreted in the feces. Most forms of supplemental calcium have similar absorption rates (9).
Kidneys
In people with normal kidney function, between 100 and 300 mg of calcium is excreted in the urine per day. Lower amounts (<80 mg/day) are excreted in those with kidney disease (14).
Skin
Small amounts of calcium are excreted via sweat. It is estimated that 10-40 mg of calcium is lost in sweat during each hour of exercise (9, 15).
Impact of other food components
The following food components may decrease calcium excretion:
- Potassium reduces urinary calcium excretion. However, this may be offset by a reduction in intestinal absorption of calcium, which results in no net changes in calcium balance (9, 16).
The following food components may increase calcium excretion:
- Caffeine increases urinary calcium excretion, but the effect is very small. Caffeine intake <400 mg/day is unlikely to negatively impact calcium status as long as calcium intake is adequate (9, 17).
- Sodium (in high amounts) increases urinary calcium excretion, but the body compensates for the loss by increasing vitamin D synthesis that leads to enhanced calcium absorption (18, 19).
- Phosphorus increases urinary calcium excretion when consumed as part of a high phosphorus, low calcium diet (20, 21).
- Protein may increase urinary calcium excretion. Some studies have shown an increase in calcium absorption with higher protein diets (9, 22, 23, 24).
How is calcium balance regulated?
Calcium balance is tightly regulated via intestinal absorption, renal excretion, and exchange from body stores, particularly bones. This process is controlled by the following hormones (9):
- Parathyroid hormone (PTH) raises serum calcium levels by stimulating bone resorption, enhancing calcium reabsorption in the kidneys, and promoting the production of calcitriol (25).
- Calcitriol (the active form of vitamin D) raises serum calcium levels by increasing calcium absorption in the intestines, enhancing calcium reabsorption in the kidneys, and stimulating bone resorption (26).
- Calcitonin (produced by the thyroid) lowers serum calcium levels by promoting calcium deposition in the bones and enhancing calcium excretion in the kidneys (27).
How does calcium interact with other nutrients?
Calcium has significant interactions with vitamin D, vitamin K, and magnesium. All are required for proper calcium metabolism.
Vitamin D
Vitamin D (also known as calcitriol) is essential for the regulation of calcium metabolism, impacting its absorption, excretion, and storage throughout the body (26, 28).
It increases calcium absorption in the intestines by stimulating the production of calcium-binding proteins like calbindin, which transport calcium into the bloodstream.
In the kidneys, vitamin D promotes calcium reabsorption, reducing the amount of calcium excreted in the urine, and thereby helping to maintain stable blood calcium levels.
Vitamin D also stimulates the release of calcium from bones into the blood when needed, ensuring an adequate supply for essential functions such as muscle contraction and nerve signaling.
Vitamin K
Vitamin K plays a critical role in regulating calcium by activating specific calcium-binding proteins that are essential for proper calcium utilization throughout the body.
In bone tissue, vitamin K activates osteocalcin, a protein secreted by osteoblasts that enables calcium to bind to the bone matrix, helping to increase bone density and strength (29).
Additionally, vitamin K activates matrix Gla-protein (MGP), which helps prevent calcification, a process in which calcium is deposited in soft tissues, such as blood vessels (30).
Magnesium
High calcium intake (>2600 mg/day) may increase the risk of magnesium deficiency by impairing magnesium absorption and increasing its excretion in the urine (31).
There is some research to suggest that calcium-to-magnesium ratios less than 1.7 may increase mortality rates, while ratios greater than 2.8 may increase chronic disease risk (32, 33, 34).
Many experts recommend a calcium-to-magnesium ratio of 2:1, meaning you should consume twice as much calcium as magnesium for optimal health (35).
So, this would mean that people who need 1300 mg of calcium should also be aiming for about 650 mg of magnesium from food and supplements each day.
How can you test calcium levels?
Bone mineral density (BMD), measured via DEXA, is the best indicator of total body, long-term calcium status. Serum calcium levels are tightly regulated and cannot rule out calcium deficiency.
Bone mineral density
What it measures
Bone mineral density (BMD) is the amount of minerals (mainly calcium and phosphorus) contained in a certain volume of bone. It is measured via dual-energy x-ray absorptiometry (DEXA) scan (36).
Collection type
Radiology (in-person scan with exposure to low levels of radiation required.)
Reference ranges
| Normal bone density | T-score greater than or equal to -1.0 (36) |
| Osteopenia | T-score between -1.0 and -2.5 (37) |
| Osteoporosis | T-score less than -2.5 (38) |
Interpretation
Bone mineral density is the best indicator of long-term calcium status. Low bone density (T-score less than -1.0) may indicate chronic calcium deficiency (39).
However, BMD is also highly dependent on factors outside of calcium intake, including genetics, hormone levels, intake of other nutrients, and lifestyle factors (smoking, physical activity, etc.).
How to order
DEXA scans must be ordered by a physician.
Verdict
Measuring bone mineral density can provide better information about calcium status than serum calcium levels, because the majority of calcium is stored in bones.
Serum total calcium
What it measures
Serum total calcium measures the amount of both free and protein-bound calcium in serum, the fluid that remains after blood cells and clotting proteins have been removed from the blood (4).
Collection type
Blood sample (phlebotomy required, typically with an overnight fast)
Reference ranges
| Normal range | 8.5-10.5 mg/dL (2.12-2.62 mmol/L) (40) |
| Hypocalcemia | <8.5 mg/dL (<2.12 mmol/L) (40) |
| Hypercalcemia | >10.5 mg/dL (>2.62 mmol/L) (40) |
Interpretation
Serum calcium is tightly regulated and accounts for just 1% of total calcium found in the body. It doesn’t reflect recent calcium intake or long-term total body calcium status (39).
Also, because a large proportion of calcium is bound to albumin in the serum, total calcium will appear falsely low if albumin is low. The following equation is used to correct for low albumin (5):
Corrected calcium (mg/dL) = reported total calcium (mg/dL) + 0.8 (4.0 – serum albumin (g/dl))
How to order
Most labs offer serum total calcium testing, including DHA Laboratory, Labcorp, Quest Diagnostics, and Vibrant (Micronutrient Panel). Many options are also available through Rupa Health.
Verdict
Serum total calcium is cheap and widely available but is not a good indicator of calcium status, except in cases of severe deficiency. A normal result doesn’t rule out calcium deficiency.
Serum ionized calcium
What it measures
Serum ionized calcium measures the amount of unbound calcium ions in the serum, the fluid that remains after blood cells and clotting proteins have been removed from the blood (4).
Collection type
Blood sample (phlebotomy required, typically with an overnight fast)
Reference ranges
| Normal range | 4.65-5.25 mg/dL (1.16-1.31 mmol/L) (40) |
| Hypocalcemia | <4.65 mg/dL (<1.16 mmol/L) (40) |
| Hypercalcemia | >5.25 mg/dL (>1.31 mmol/L) (40) |
Interpretation
Only ionized (free) calcium is physiologically active, so measuring it can provide a more accurate picture of calcium metabolism than total calcium (39, 41).
Still, serum calcium (total or ionized) is a poor indicator of overall calcium status, because it is tightly regulated.
How to order
Most labs offer serum ionized calcium testing, including DHA Laboratory, Labcorp, and Quest Diagnostics. It is also available through Rupa Health.
Verdict
Compared to total calcium, ionized calcium is a slightly better indicator of calcium status, but it still isn’t recommended for evaluating long-term, total body calcium (42).
Other markers
- Hair tissue mineral analysis (HTMA) shows how much calcium has been lost in the hair. It may offer insights about calcium status, but more research is needed (43, 44, 45, 46).
How common is calcium deficiency?
It is estimated that 3.5 billion people worldwide are at risk for calcium deficiency due to inadequate calcium intake (47).
Many Americans don’t consume enough calcium. NHANES data from 2017-2018 shows an average dietary intake of 1079 mg/day for men and 860 mg/day for women (48).
This meets the RDA for men between the ages of 19-70 years old (1,000 mg/day), but is 14% short for women ages 19-50 (1,000 mg/day) and 28% short for women over 50 years old (1,200 mg/day).
What are the signs and symptoms of calcium deficiency?
Acute hypocalcemia (serum total calcium <8.5 mg/dL) may result in the following signs and symptoms (40):
- Anxiety
- Cardiac arrhythmias
- Depression
- Muscle spasms
- Paresthesias
- Seizures
- Tetany
Long-term hypocalcemia can also lead to (4):
- Brittle nails
- Cataracts
- Coarse hair
- Dental problems
- Dry skin
- Itchy skin
- Psoriasis
What are the potential long-term consequences of calcium deficiency?
Inadequate calcium intake has been associated with the following negative health consequences:
What causes calcium deficiency?
Calcium deficiency can be caused by any of the following factors:
Dietary intake
Genetic factors
Increased needs
- Breastfeeding (57)
Malabsorption
- Celiac disease (58, 59)
- Chronic kidney disease (60)
- Chronic pancreatitis (61)
- Excessive alcohol intake (62)
- Inflammatory bowel disease (63)
- Smoking (64)
- Vitamin D deficiency (65)
Medications
- Anticonvulsants (carbamazepine, phenobarbital, phenytoin) (66)
- Bisphosphonates (alendronate, risedronate, etidronate) (67)
- Glucocorticoids (prednisolone, dexamethasone) (68)
- Loop diuretics (furosemide, bumetanide, torsemide) (69)
- Proton pump inhibitors (PPIs) (omeprazole, pantoprazole) (70)
Other causes
How much calcium do you need each day?
The Recommended Dietary Allowance (RDA) for calcium is listed below (1):
| Age/status | Males | Females |
| Birth-6 months | 200 mg* | 200 mg* |
| 7-12 months | 260 mg* | 260 mg* |
| 1-3 years old | 700 mg | 700 mg |
| 4-8 years old | 1,000 mg | 1,000 mg |
| 9-13 years old | 1,300 mg | 1,300 mg |
| 14-18 years old | 1,300 mg | 1,300 mg |
| 19-30 years old | 1,000 mg | 1,000 mg |
| 31-50 years old | 1,000 mg | 1,000 mg |
| 51-70 years old | 1,000 mg | 1,200 mg |
| >70 years old | 1,200 mg | 1,200 mg |
| Pregnancy | Requirements do not increase. | |
| Breastfeeding | Requirements do not increase. | |
| *This is an Adequate Intake (AI), not an RDA. | ||
How much calcium is needed to correct a deficiency?
Severe hypocalcemia requires treatment with intravenous calcium. Typically, calcium gluconate is administered at a dose of 1,000 to 2,000 mg or until serum calcium levels normalize (40).
Mild hypocalcemia can be treated with 1,500 to 2,000 mg/day of elemental calcium, split into 500 mg doses throughout the day, until lab results normalize.
It’s important to note that hypocalcemia can’t be corrected if there is an underlying magnesium or vitamin D deficiency. These nutrients must be replenished before starting calcium supplements.
Is calcium toxicity a concern?
Calcium toxicity, called hypercalcemia, occurs in 1-2% of the general population (74).
Hypercalcemia is defined as a serum total calcium level greater than 10.5 mg/dL and is typically caused by one of the following:
- Hyperparathyroidism (due to the effect of PTH on serum calcium levels)
- Medications (including thiazide diuretics, calcium-based antacids, and lithium)
- Vitamin D toxicity (due to vitamin D’s effects on calcium absorption and excretion)
It is very difficult (or maybe impossible) to develop calcium toxicity from food alone. Excessive calcium intake is more likely to occur with calcium supplementation (75).
Signs and symptoms of calcium toxicity
Mild hypercalcemia (serum total calcium 10.5-11.9 mg/dL) is usually asymptomatic but can increase the risk of kidney stones, pancreatitis, and peptic ulcers over the long term (4, 74).
Moderate hypercalcemia (serum total calcium 12.0-13.9 mg/dL) can cause anxiety, depression, nausea, vomiting, constipation, anorexia, fatigue, weakness, muscle pain, polyuria, polydipsia, dehydration, confusion, and cardiac arrhythmias.
Severe hypercalcemia (serum total calcium 14.0-16.0 mg/dL) may lead to coma and cardiac arrest.
Treatment for calcium toxicity
Calcium toxicity treatment varies based on the severity of hypercalcemia, presenting symptoms, and underlying cause but may include any of the following (74):
- Hydration: Intravenous fluids (usually saline) help dilute calcium and promote its excretion through urine.
- Medications: Calcitonin and bisphosphonates may be used to lower serum calcium levels. Glucocorticoids can also reduce intestinal calcium absorption.
- Treat the underlying cause: This may involve managing conditions like hyperparathyroidism or malignancies.
- Consider dialysis: In severe or resistant cases, dialysis may be needed to remove excess calcium, particularly in patients with kidney dysfunction.
The prognosis of hypercalcemia depends on its cause, with benign conditions generally having favorable outcomes and malignancy-linked hypercalcemia often leading to poor prognosis.
What is the upper limit for calcium?
For total calcium intake (both dietary and supplemental), the Tolerable Upper Intake Levels (ULs) are as follows (75):
| Age | Males | Females |
| Birth-6 months | 1,000 mg | 1,000 mg |
| 6-12 months | 1,500 mg | 1,500 mg |
| 1-8 years old | 2,500 mg | 2,500 mg |
| 9-18 years old | 3,000 mg | 3,000 mg |
| 19-50 years old | 2,500 mg | 2,500 mg |
| 51+ years old | 2,000 mg | 2,000 mg |
The UL represents the maximum amount of calcium that most people can consume each day without increasing the risk for kidney stones, cardiovascular disease, and other adverse effects (75).
Some experts have argued that the UL for calcium is too low, as higher calcium intakes have been well-tolerated in several newer studies. However, more research is needed (76).
What are the best food sources of calcium?
The best calcium sources are milk, yogurt, cheese, and fortified plant-based dairy alternatives. Other good sources include dark leafy greens, beans, nuts, seeds, and fish canned with bones.
Animal-based food sources of calcium
| Food | Serving size | Calcium content |
| Buffalo milk | 1 cup (244 grams) | 412 mg |
| Sardines (canned w/ bones) | 3.5 ounces (100 grams) | 382 mg |
| Parmesan cheese | 1 ounce (28 grams) | 335 mg |
| Goat’s milk | 1 cup (244 grams) | 327 mg |
| Cow’s milk | 1 cup (244 grams) | 305 mg |
| Ricotta cheese | ½ cup (123 grams) | 305 mg |
| Kefir | 1 cup (244 grams) | 303 mg |
| Yogurt | 1 cup (245 grams) | 296 mg |
| Buttermilk | 1 cup (244 grams) | 281 mg |
| American cheese | 1 ounce (28 grams) | 260 mg |
| Swiss cheese | 1 ounce (28 grams) | 252 mg |
| Greek yogurt | 1 cup (245 grams) | 245 mg |
| Mackerel (canned w/ bones) | 3.5 ounces (100 grams) | 241 mg |
| Salmon (canned w/ bones) | 3.5 ounces (100 grams) | 239 mg |
| Queso cotija | 1 ounce (28 grams) | 224 mg |
| Provolone cheese | 1 ounce (28 grams) | 214 mg |
| Cheddar cheese | 1 ounce (28 grams) | 199 mg |
| Queso añejo | 1 ounce (28 grams) | 193 mg |
| Queso asadero | 1 ounce (28 grams) | 187 mg |
| Queso chihuahua | 1 ounce (28 grams) | 185 mg |
| Paneer | 1 ounce (28 grams) | 167 mg |
| Queso fresco | 1 ounce (28 grams) | 160 mg |
| Halloumi | 1 ounce (28 grams) | 150 mg |
| Blue cheese | 1 ounce (28 grams) | 150 mg |
| Mozzarella cheese | 1 ounce (28 grams) | 143 mg |
| Feta cheese | 1 ounce (28 grams) | 140 mg |
| Cottage cheese | ½ cup (105 grams) | 108 mg |
| Ice cream | ½ cup (66 grams) | 85 mg |
| Sour cream | 2 tablespoons (30 grams) | 30 mg |
| Cream cheese | 2 tablespoons (30 grams) | 29 mg |
| Heavy cream | 1 tablespoon (15 mL) | 10 mg |
Plant-based food sources of calcium
| Food | Serving size | Calcium content |
| Plant-based milks (fortified) | 1 cup (240 mL) | 350-450 mg (77, 78, 79) |
| Orange juice (w/ added calcium) | 1 cup (248 grams) | 350 mg |
| Plant-based yogurts (fortified) | ¾ cup (170 grams) | 150-300 mg (80, 81, 82) |
| Tofu | 3.5 ounces (100 grams) | 282 mg |
| Natto (fermented soybeans) | 3.5 ounces (100 grams) | 217 mg |
| Blackstrap molasses | 1 tablespoon (21 grams) | 200 mg |
| Chia seeds | 1 ounce (28 grams) | 179 mg |
| Rhubarb (cooked) | ½ cup (120 grams) | 174 mg |
| Okra (cooked) | 1 cup (160 grams) | 142 mg |
| Collard greens (cooked) | ½ cup (95 grams) | 134 mg |
| Tahini (sesame seed butter) | 2 tablespoons (30 grams) | 128 mg |
| Spinach (cooked) | ½ cup (90 grams) | 123 mg |
| Cactus (cooked) | ½ cup (75 grams) | 123 mg |
| Winged beans (cooked) | ½ cup (86 grams) | 122 mg |
| Almond butter | 2 tablespoons (32 grams) | 111 mg |
| Kale (raw) | 2 cups (42 grams) | 107 mg |
| Dandelion greens (cooked) | ½ cup (55 grams) | 107 mg |
| Turnip greens (cooked) | ½ cup (72 grams) | 99 mg |
| Tempeh (cooked) | 3.5 ounces (100 grams) | 96 mg |
| Bok choy (cooked) | ½ cup (85 grams) | 93 mg |
| Acorn squash (cooked) | 1 cup (205 grams) | 90 mg |
| Kale (cooked) | ½ cup (59 grams) | 89 mg |
| Carob (unsweetened) | 1 ounce (28 grams) | 86 mg |
| Butternut squash (cooked) | 1 cup (205 grams) | 84 mg |
| Mustard greens (cooked) | ½ cup (70 grams) | 83 mg |
| Prickly pears | 1 cup (149 grams) | 83 mg |
| Sweet potatoes (baked) | 1 cup (200 grams) | 76 mg |
| Almonds | 1 ounce (28 grams) | 76 mg |
| Broccoli (cooked) | 1 cup (155 grams) | 74 mg |
| Oranges | 1 fruit (154 grams) | 65 mg |
| Figs (dried) | ¼ cup (40 grams) | 65 mg |
| Navy beans (cooked) | ½ cup (91 grams) | 63 mg |
| Teff (cooked) | ½ cup (126 grams) | 62 mg |
| Great Northern beans (cooked) | ½ cup (89 grams) | 60 mg |
| Spinach (raw) | 2 cups (60 grams) | 59 mg |
| Amaranth (cooked) | ½ cup (123 grams) | 58 mg |
| Green beans (cooked) | 1 cup (125 grams) | 55 mg |
| Goji berries (dried) | 1 ounce (28 grams) | 53 mg |
| Swiss chard (cooked) | ½ cup (88 grams) | 51 mg |
| Edamame (shelled) | ½ cup (78 grams) | 48 mg |
| Ready-to-eat cereals (fortified) | varies | varies |
Is water a significant source of calcium?
The amount of calcium in drinking water varies widely depending on the source and decreases when water is softened, a process that removes minerals from water (83).
An older study found that North American tap water contributed 8-16% of daily calcium requirements for every 2 liters, while European bottled water provided 20-58% per liter (84).
Here’s the calcium content of some commercially available bottled waters:
| Brand | Calcium content (mg/L) | Calcium content (mg/cup) |
| ROI | 610 mg/L | 144 mg/cup |
| Gerolsteiner | 348 mg/L | 82 mg/cup |
| Perrier | 160 mg/L | 39 mg/cup |
| S. Pellegrino | 160 mg/L | 38 mg/cup |
| Evian | 80 mg/L | 19 mg/cup |
| FIJI Water | 18 mg/L | 4 mg/cup |
| Smartwater | <1 mg/L | <0.3 mg/cup |
Which conditions might benefit from increased calcium intake?
Increasing calcium intake (via food or supplements) may be beneficial for the following conditions:
1. Bariatric surgery
A 2023 meta-analysis found that 7% of people with a history of bariatric surgery, especially roux-en-y gastric bypass, were deficient in calcium based on low serum levels (85).
Roux-en-y gastric bypass increases the risk of calcium more than other types of surgery because it bypasses the duodenum and proximal jejunum, the main sites of absorption for calcium (86).
Following bariatric surgery, guidelines recommend supplementing with 1,200-1,500 mg/day of calcium (as calcium citrate), in addition to vitamin D (at least 3,000 IU/day) (87).
2. Hypertension
Calcium regulates blood pressure via several mechanisms, including the modification of intracellular calcium in smooth muscle cells of blood vessels (88).
It may be helpful for preventing high blood pressure. Each 500 mg/day increment in dietary calcium intake is associated with a 7% reduction in hypertension risk (50).
Similarly, a 2022 meta-analysis found that calcium supplementation (1,000-1,500 mg/day) significantly reduced both SBP and DBP in people without hypertension (89).
3. Hypoparathyroidism
Hypoparathyroidism is an endocrine disorder that causes parathyroid hormone deficiency. This leads to hypocalcemia (low serum calcium) and hyperphosphatemia (high serum phosphate) (71).
It is treated primarily with calcium (500-3,000 mg/day) and calcitriol (0.25-3 mcg/day), though some people need parathyroid hormone replacement therapy.
4. Preeclampsia
Lower serum calcium levels are common in women with preeclampsia, a complication of pregnancy that results in high blood pressure and (if untreated) organ damage (90, 91).
The World Health Organization (WHO) recommends that pregnant women with low dietary calcium intake take calcium supplements (1,500-2,000 mg/day) to reduce the risk of preeclampsia (92).
However, a 2022 meta-analysis of 25 RCTs found that low-dose (<1,000 mg/day) calcium supplementation was just as effective as higher doses (>/=1,000 mg/day) (93).
5. Premenstrual Syndrome (PMS)
People with PMS often have lower calcium levels and may experience further drops due to rising estrogen during the luteal phase of their menstrual cycle (94).
This could disrupt the production and release of neurotransmitters, such as serotonin, resulting in symptoms like mood swings, irritability, and depression.
Research has shown that some symptoms of PMS are reduced by calcium supplementation (500-1,200 mg/day) when taken for at least 2 months (95, 96, 97, 98, 99, 100).
6. Colorectal cancer
Calcium may help protect against colorectal cancer by supporting healthy cell growth and binding to bile acids, reducing their potential to damage the intestinal lining (101).
A small number of trials have found a reduced colorectal cancer risk with calcium supplementation (1200-2000 mg/day) (102, 103).
In addition, several studies show a link between higher calcium intake (>1000 mg/day) and a lower risk of death in people with colorectal cancer (104, 105).
7. Osteoporosis
Calcium supports bone mineralization and protects against bone loss, so it is thought that adequate calcium intake may help prevent osteoporosis.
When combined with vitamin D, there is some evidence that calcium supplementation (500-1,200 mg/day) reduces the risk of hip fracture in postmenopausal women (106).
However, overall research doesn’t support the use of calcium supplements for preventing fractures in people without osteoporosis, regardless of age (107, 108).
Most guidelines for osteoporosis prevention and treatment only recommend using calcium supplements if dietary intake is inadequate (below the RDA) (109, 110, 111, 112).
What are some of the different forms of supplemental calcium?
Calcium carbonate is the most common form and is well absorbed when taken with food. Calcium citrate can be taken with or without food and is a better choice for people with low stomach acid.
| Type of calcium | Bioavailability | Common uses | |
| Calcium acetateMade by combining calcium with acetic acid, a byproduct of fermentation that is also the main component of vinegar. It contains 25% elemental calcium (113, 114, 115). | High (32%) (116) | Used primarily as a phosphate binder in people with chronic kidney disease (117). | |
| Calcium carbonate (also called coral calcium)An inorganic compound that contains 40% elemental calcium along with carbon and oxygen. It is found naturally in rocks, coral, and oyster shells, and is used as the active ingredient in many antacids (118, 119). | High (24-39%), but only when stomach acid is adequate and taken with food (120) | Used as an antacid, phosphate binder, or a supplement. Not ideal for people with low stomach acid (121). | |
| Calcium citrateMade by combining calcium with citric acid, and organic acid found in citrus fruits. It contains 21% elemental calcium (119, 122). | Moderate-high (24-30%), but has a higher absorption rate than calcium carbonate when taken without food or in people with low stomach acid (120, 123). | Used for general supplementation, especially in people with low stomach acid. | |
| Calcium citrate malateMade by combining calcium with citric acid and malic acid, an organic acid that is responsible for the tart flavor of many fruits. It contains 24% elemental calcium (124, 125). | High (36-44%), even when taken without food or in people with low stomach acid (125) | Used for general supplementation, especially in people with low stomach acid, and food fortification (mainly orange juice). | |
| Calcium formateMade by combining calcium with formic acid, an organic acid found naturally in fruits, vegetables, and insect venom. It contains 31% elemental calcium (126, 127). | High (higher than citrate and carbonate forms when taken without food) (127) | Used primarily as a preservative. | |
| Calcium gluconateMade by combining calcium with gluconic acid, an oxidation product of glucose found naturally in fruit, honey, and wine (128).It contains 9% elemental calcium (119). | Moderate (27%) (116) | Used primarily intravenously in acute care settings to correct hypocalcemia and cardiac arrhythmias (129). | |
| Calcium lactateMade by combining calcium with lactic acid, a byproduct of carbohydrate metabolism. It contains 13% elemental calcium (119, 130). | High (32-47%) (116, 131) | Used primarily as a food additive rather than a supplement due to its low calcium concentration (13%) (132). | |
| Calcium malate (also called dicalcium malate)Made by combining calcium with malic acid, an organic acid that is responsible for the tart flavor of many fruits. It contains 29% elemental calcium (124, 133). | Unknown | Used for general supplementation and bone health. | |
| Calcium phosphate (tricalcium phosphate)An inorganic compound found naturally in soil, rocks, and bones. It contains 38% elemental calcium (115, 134) | Moderate (25%) (120, 135) | Used for general supplementation, bone health, and as an antacid. | |
| Microcrystalline hydroxyapatite A mineral complex derived from bones (usually bovine) that contains calcium, phosphate, and bone-specific growth peptides. It contains 40% elemental calcium (119, 136, 137). | Low-moderate (17%) when taken without food (138) | Used for general supplementation and bone health. | |
Which calcium supplements are recommended?
There are many many different brands and forms of calcium available. Below are some commonly used and recommended options:
Calcium capsules and tablets
Calcium carbonate (coral calcium)
- NatureMade Calcium 500 mg with D3
- Contains 500 mg calcium (as calcium carbonate) and 10 mcg (400 IU) vitamin D3 (as cholecalciferol) per serving (1 tablet)
- Other ingredients: cellulose gel, maltodextrin, croscarmellose sodium, hypromellose, magnesium stearate, corn starch, and polyethylene glycol
- NatureMade Calcium 600 mg with D3
- Contains 600 mg calcium (as calcium carbonate) and 10 mcg (400 IU) vitamin D3 (as cholecalciferol) per serving (1 tablet)
- Other ingredients: cellulose gel, hypromellose, maltodextrin, croscarmellose sodium, polyethylene glycol, and magnesium stearate
Calcium citrate/malate
- Designs for Health Calcium Malate (Fullscript link)
- Contains 500 mg calcium (as dicalcium malate) and 2.5 mcg (100 IU) vitamin D (as cholecalciferol) per serving (2 capsules)
- Other ingredients: cellulose (capsule), microcrystalline cellulose, and stearates (vegetable source)
- Pure Encapsulations Calcium Citrate (Fullscript link)
- Contains 300 mg calcium (as calcium citrate) per serving (2 capsules)
- Other ingredients: vegetarian capsule (cellulose, water) and ascorbyl palmitate
- Thorne Calcium (Fullscript link)
- Contains 250 mg calcium (as dicalcium malate) per serving (1 capsule)
- Other ingredients: hypromellose (derived from cellulose) capsule and medium chain triglyceride oil
- Vital Nutrients Calcium Citrate/Malate (Fullscript link)
- Contains 300 mg calcium (as calcium citrate malate and dicalcium malate) per serving (2 capsules)
- Other ingredients: hypromellose and ascorbyl palmitate
Microcrystalline hydroxyapatite
- NOW Foods Calcium Hydroxyapatite
- Contains 500 mg calcium (as microcrystalline hydroxyapatite) and 200 mg phosphorus (as microcrystalline hydroxyapatite) per serving (2 capsules)
- Other ingredients: bovine gelatin (capsule) and magnesium stearate (vegetable source)
- Pure Encapsulations Calcium (MCHA) (Fullscript link)
- Contains 250 mg calcium (as microcrystalline hydroxyapatite) (bovine) per serving (1 capsule)
- Other ingredients: vegetarian capsule (cellulose, water)
Powdered calcium
- NOW Foods Calcium Carbonate Powder
- Contains 600 mg calcium (as calcium carbonate) per serving (½ teaspoon)
- Other ingredients: none
- NOW Foods Calcium Citrate Powder (Fullscript link)
- Contains 600 mg calcium (as calcium citrate) per serving (1½ teaspoons)
- Other ingredients: none
Liquid calcium
- Trace Minerals Liquid Ionic Calcium (unflavored) (Fullscript link)
- Contains 200 mg calcium (as calcium chloride) and 50 mg ionic trace minerals complex per serving (¼ teaspoon)
- Other ingredients: purified water and non-GMO citric acid
Calcium w/ magnesium
Calcium w/ magnesium capsules and tablets
- Designs for Health Cal/Mag 2:1 (Fullscript link)
- Contains 300 mg calcium (as dicalcium malate) and 150 magnesium (as dimagnesium malate) per serving (2 capsules)
- Other ingredients: cellulose (capsule) and vegetable stearate
- Designs for Health Cal/Mag 1:1 (Fullscript link)
- Contains 200 mg calcium (as dicalcium malate) and 200 mg magnesium (as dimagnesium malate) per serving (2 capsules)
- Other ingredients: cellulose (capsule), microcrystalline cellulose, and vegetable stearate
- Pure Encapsulations Calcium Magnesium (Citrate) (Fullscript link)
- Contains 240 mg calcium (as calcium citrate) and 240 magnesium (from magnesium citrate) per serving (3 capsules)
- Other ingredients: vegetarian capsule (cellulose, water) and ascorbyl palmitate
- Pure Encapsulations Calcium (MCHA) with Magnesium (Fullscript link)
- Contains 140 mg calcium (as microcrystalline hydroxyapatite) (bovine) and 70 mg magnesium (as magnesium citrate) per serving (1 capsule)
- Other ingredients: vegetarian capsule (cellulose, water) and ascorbyl palmitate
- Thorne Calcium-Magnesium Malate (Fullscript link)
- Contains 100 mg calcium (as calcium malate) and 100 mg magnesium (as magnesium malate) per serving (1 capsule)
- Other ingredients: hypromellose (derived from cellulose) capsule and medium chain triglyceride oil
Calcium w/ magnesium powder
- DaVinci Labs Cal-Mag Citrate Powder (Fullscript link)
- Contains 600 mg calcium (as calcium citrate), 300 mg magnesium (as magnesium citrate), and 2.5 mcg (100 IU) vitamin D2 (as ergocalciferol) per serving (1 scoop)
- Other ingredients: none
- NOW Foods Calcium & Magnesium Powder (Fullscript link)
- Contains 400 mg calcium (as calcium citrate), 400 mg magnesium (as magnesium citrate), and 5 mcg (200 IU) vitamin D3 (as cholecalciferol) per serving (1.5 teaspoons)
- Other ingredients: none
Calcium w/ magnesium liquid
- Douglas Labs Liquid Cal/Mag/D (raspberry flavor) (Fullscript link)
- Contains 350 mg calcium (as calcium citrate), 175 magnesium (as magnesium citrate), and 25 mcg vitamin D3 (as cholecalciferol) per serving (2 teaspoons)
- Other ingredients: purified water, xylitol, natural raspberry flavor, medium chain triglycerides, citric acid, xanthan gum, organic stevia leaf extract, potassium sorbate, rosemary leaf extract, and natural mixed tocopherols
- Integrative Therapeutics Liquid Calcium Magnesium 1:1 (berry flavor) (Fullscript link)
- Contains 500 mg calcium (as calcium magnesium citrate), 500 mg magnesium (as calcium magnesium citrate and magnesium citrate), and 5 mcg (200 IU) vitamin D3 (as cholecalciferol) per serving (1 tablespoon)
- Other ingredients: purified water, glycerin, natural flavors, citric acid, xanthan gum, and potassium sorbate
- Integrative Therapeutics Liquid Calcium Magnesium 2:1 (orange-vanilla flavor) (Fullscript link)
- Contains 600 mg calcium (as calcium magnesium citrate), 300 g magnesium (as calcium magnesium citrate), and 10 mcg (400 IU) vitamin D3 (as cholecalciferol) per serving (1 tablespoon)
- Other ingredients: purified water, citric acid, glycerin, natural flavors, xanthan gum, and potassium sorbate
- Pure Encapsulations Cal/Mag/D Liquid (raspberry flavor) (Fullscript link)
- Contains 350 mg calcium (as calcium citrate), 175 mg magnesium (as magnesium citrate), and 25 mcg (1,000 IU) vitamin D3 per serving (2 teaspoons)
- Other ingredients: purified water, xylitol, natural raspberry flavor, citric acid, medium chain triglycerides, xanthan gum, purified stevia leaf extract, potassium sorbate, rosemary extract, and natural mixed tocopherols
Bone support w/ calcium
- AlgaeCal Plus (Fullscript link)
- Contains 720 mg calcium per serving (4 capsules)
- Other nutrients: magnesium, vitamin D3, vitamin K2, boron, vitamin C, potassium, copper, manganese, silicon, nickel, phosphorus, selenium, strontium, vanadium, and zinc
- Other ingredients: vegetable cellulose (vegetarian capsule), magnesium stearate (vegetable grade), and microcrystalline cellulose
- Designs for Health OsteoBen (Fullscript link)
- Contains 400 mg calcium (as dicalcium malate) per serving (4 capsules)
- Other nutrients: vitamin D, vitamin K1/K2, magnesium, zinc, and genistein
- Other ingredients: cellulose (capsule), dicalcium phosphate, and vegetable stearate
- Designs for Health OsteoForce (Amazon link)
- Contains 500 mg calcium (as calcium ascorbate) per serving (4 capsules)
- Other nutrients: vitamin C, vitamin D, vitamin K, magnesium, zinc, copper, manganese, vitamin E isomers, trans-geranylgeraniol, and boron
- Other ingredients: cellulose (capsule), microcrystalline cellulose, and vegetable stearate
- Thorne Advanced Bone Support (Fullscript link)
- Contains 300 mg calcium (as dicalcium malate) per serving (2 capsules)
- Other nutrients: vitamin D, vitamin B6, folate, vitamin B12, magnesium, and boron
- Other ingredients: hypromellose (derived from cellulose) capsule and medium chain triglyceride oil
- Trace Minerals Coral Calcium (Fullscript link)
- Contains 450 mg calcium (as coral calcium) per serving (2 capsules)
- Other ingredients: vitamin C, vitamin D, magnesium, zinc, chloride, boron, and ionic trace mineral complex
- Other ingredients: stearic acid, hypromellose, microcrystalline cellulose, and magnesium stearate
- Trace Minerals Research Cal/Mag/Zinc (Fullscript link)
- Contains 1200 mg calcium (as tricalcium phosphate, calcium citrate, and calcium gluconate) per serving (2 tablespoons liquid)
- Other nutrients: vitamin D3, iron, phosphorus, magnesium, zinc, chloride, sodium, boron, and ionic trace minerals complex
- Other ingredients: purified water, natural vegetable glycerin, natural strawberry flavor, citric acid, phosphoric acid, xanthan gum, potassium benzoate, and potassium sorbate
How to take calcium supplements
Most forms of supplemental calcium should be taken with food to enhance absorption, as stomach acid produced during digestion helps the body more effectively absorb the calcium (129, 139).
Calcium citrate, however, does not rely on stomach acid and can be taken with or without food, making it a more flexible option for those with digestive concerns.
It’s important to limit each dose to 500 mg or less (of elemental calcium), because higher amounts are absorbed less efficiently and increase the risk of gastrointestinal side effects.
Do calcium supplements have any adverse effects or risks?
Constipation is the most common side effect of calcium supplementation. There is also some concern about increased cardiovascular disease risk, though research is inconclusive.
Gastrointestinal upset
Calcium supplements can cause gastrointestinal side effects, especially constipation and gas, because calcium slows down intestinal motility (121, 129, 140).
These issues are more common with calcium carbonate, which requires stomach acid for absorption and can be more difficult to digest (141).
You can reduce the risk of side effects by choosing a highly bioavailable form (such as calcium citrate), splitting up larger doses throughout the day, and taking them with food (129).
Cardiovascular disease
Some studies have suggested that taking calcium supplements (>1000 mg/day), particularly without accompanying vitamin D, may be associated with an increased risk of heart attack (142, 143, 144).
The hypothesis is that high doses of supplemental calcium could lead to hypercalcemia, which might contribute to the calcification of arteries, a known risk factor for heart disease (145).
However, research is conflicting, with several meta-analyses showing no link between calcium supplements and cardiovascular disease (144, 146, 147, 148, 149).
Larger trials focusing specifically on the effect of calcium supplements on CVD risk are needed before any conclusions can be made (150).
Medication interactions
When taken together, calcium supplements can decrease the absorption and effectiveness of certain medications, including the following:
It is typically recommended to avoid taking calcium supplements within 2-4 hours of these medications.
Who should be cautious with calcium supplementation?
People with impaired kidney function, a history of calcium-containing kidney stones, or conditions that cause hypercalcemia should be cautious with calcium supplements.
Kidney disease
Conditions that impair kidney function increase the risk of developing hypercalcemia from calcium supplements, as the kidneys are unable to effectively excrete excess calcium (60).
Kidney stones
Calcium supplements may increase kidney stone risk, particularly if they are taken in excess, without adequate vitamin D, or without food, because this increases urinary calcium excretion (155).
Those with a personal or family history of calcium-containing kidney stones are advised to avoid calcium supplements unless prescribed by a healthcare professional (156).
Hypercalcemia
People with conditions that cause hypercalcemia (high serum calcium levels), such as hyperparathyroidism, should check with their doctor before starting calcium supplementation (74).
Amy Richter is a Registered Dietitian Nutritionist based in Missouri. She's an alumnus of Integrative & Functional Nutrition Academy (IFNA) and a nutrition writer/medical advisor for Healthline and Medical News Today. Amy's favorite activity is translating complex science into easy-to-understand articles for practitioners and laypeople.