What Calcium Is
Calcium is the most abundant mineral in the human body, with about 99% stored in bones and teeth, and the remaining 1% circulating in blood, muscles, and other tissues. It's an essential mineral, meaning your body cannot produce it and must obtain it through diet or supplementation.
Functions and Uses in the Body
Calcium serves multiple critical roles beyond just building strong bones. It's essential for muscle contraction, including the beating of your heart. Every time a muscle contracts, calcium is released, and when it relaxes, calcium is pumped back out. It's also crucial for nerve signal transmission, allowing your brain to communicate with every part of your body. Calcium plays a vital role in blood clotting (without adequate calcium, even a small cut could be dangerous), and it helps regulate enzyme activity and hormone secretion throughout your body.
Benefits of Adequate Calcium Intake
The most well-known benefit is maintaining bone density and strength, which is particularly important for preventing osteoporosis later in life. Peak bone mass is built during childhood and adolescence, making calcium intake during these years critically important. For adults, adequate calcium helps slow the natural bone loss that occurs with aging. Calcium may also help with blood pressure regulation, with some studies showing it can contribute to lower blood pressure levels. There's emerging evidence it may play a role in weight management and reducing the risk of colon cancer, though more research is needed in these areas.
Potential Negatives and Risks
Taking too much calcium, particularly from supplements, can lead to several problems. Excessive supplementation has been associated with an increased risk of kidney stones, especially in people prone to them. There's also controversial evidence suggesting very high calcium supplement intake might be linked to cardiovascular issues, though this remains debated in the scientific community. High calcium intake can interfere with the absorption of other important minerals like iron, zinc, and magnesium. Constipation is a common side effect of calcium supplements, particularly calcium carbonate. Some people also experience bloating or gas.
Recommended Intake and Serving Sizes
Daily Recommended Amounts:
Adults aged 19-50: 1,000 mg per day
Women over 50 and men over 70: 1,200 mg per day
Adolescents aged 9-18: 1,300 mg per day
Upper tolerable limit: 2,500 mg/day (adults up to 50), 2,000 mg/day (over 50)
When supplementing, it's best to take doses of no more than 500-600 mg at a time, as your body can only absorb that much calcium efficiently in one sitting. If you need 1,000 mg of supplemental calcium, split it into two doses taken at different times of day.
What to Take With Calcium
Vitamin D is the most important companion to calcium. Without adequate vitamin D, your body can only absorb about 10-15% of dietary calcium, but with sufficient vitamin D, absorption increases to 30-40%. Most calcium supplements now include vitamin D for this reason. Aim for at least 600-800 IU of vitamin D daily, though many experts recommend higher amounts.
Magnesium works synergistically with calcium and is necessary for calcium metabolism. A good ratio is about 2:1 calcium to magnesium. Magnesium deficiency can actually impair calcium absorption and bone health.
Vitamin K2 (specifically the MK-7 form) helps direct calcium to bones and teeth rather than allowing it to deposit in soft tissues like arteries. This is increasingly recognized as important for both bone and cardiovascular health.
What NOT to Take With Calcium
Iron supplements should not be taken simultaneously with calcium, as calcium significantly inhibits iron absorption. Separate them by at least two hours.
Thyroid medication (levothyroxine) can have its absorption reduced by up to 30% when taken with calcium. Take thyroid medication on an empty stomach and wait at least 4 hours before taking calcium.
Some antibiotics, particularly tetracyclines and fluoroquinolones, bind to calcium and become inactive. Separate these by at least 2-3 hours.
Bisphosphonates (osteoporosis medications) are severely affected by calcium. These must be taken on an empty stomach with water only, and you should wait at least 30 minutes before consuming calcium.
High-fiber foods or supplements can reduce calcium absorption, so avoid taking calcium supplements with very high-fiber meals or fiber supplements.
Caffeine and sodium can increase calcium excretion through urine, though this is generally only a concern with very high intake.
Who Should Take Calcium Supplements
People who don't get enough calcium from their diet (need about 3-4 servings of dairy or calcium-rich foods daily)
Postmenopausal women at high risk for bone loss
Those with osteoporosis or osteopenia
People with lactose intolerance who avoid dairy
Vegans who don't consume fortified foods
Individuals with malabsorption conditions like celiac disease or Crohn's disease
People on long-term corticosteroid therapy
Those who've had bariatric surgery
Who Should Avoid or Be Cautious With Calcium Supplements
People with a history of kidney stones (especially calcium oxalate stones)
Those with hypercalcemia (high blood calcium levels)
People with kidney disease
Individuals with a history of cardiovascular disease (should discuss with doctor)
Those with hyperparathyroidism or sarcoidosis
People taking calcium channel blockers for blood pressure
Deficiency Symptoms
Early calcium deficiency is often silent, but over time symptoms can develop:
Muscle cramps and spasms, particularly in the legs and at night
Numbness and tingling in the fingers and around the mouth
Abnormal heart rhythms
Dental problems including weak teeth and increased cavities
Osteopenia and eventually osteoporosis (long-term deficiency)
Confusion, memory problems, depression
In extreme cases, seizures (rare, usually due to specific medical conditions)
Toxicity Symptoms
Calcium toxicity (hypercalcemia) is rare from diet alone but can occur from excessive supplementation:
Nausea, vomiting, and loss of appetite
Excessive thirst and frequent urination
Constipation and abdominal pain
Confusion, lethargy, and difficulty concentrating
Irregular heart rhythms
Kidney stones
Calcium deposits in soft tissues
Chronic excessive intake can lead to kidney damage
Milk-alkali syndrome (with very high calcium and antacid intake)
Timing: When to Take Calcium
Calcium Carbonate (most common form):
Should be taken WITH MEALS
Requires stomach acid for absorption
About 40% elemental calcium
Found in products like Tums and standard calcium supplements
Calcium Citrate:
Can be taken WITH or WITHOUT food
Doesn't require stomach acid for absorption
Better for older adults or those taking acid-reducing medications
About 21% elemental calcium
General timing recommendations:
Split doses throughout the day (no more than 500-600 mg at once)
Many people take calcium at dinner or before bed
Morning and evening split is also effective
Food vs. Empty Stomach
Calcium carbonate should always be taken with food for optimal absorption
Calcium citrate is flexible and absorbs well either way
Taking with meals reduces stomach upset
Presence of other nutrients in food can enhance absorption
Types of Calcium Supplements
Calcium Carbonate:
Most common and least expensive
40% elemental calcium
Requires stomach acid
Take with food
Can cause constipation or gas
Calcium Citrate:
More expensive
21% elemental calcium
No stomach acid needed
Can take anytime
Better tolerated, less constipation
Other forms:
Calcium phosphate: Similar to carbonate
Calcium lactate and calcium gluconate: Lower elemental calcium content, require more pills
Food Sources of Calcium
Dairy Products:
Milk (1 cup): 300 mg
Yogurt (1 cup): 300-450 mg
Cheese (1.5 oz): 300 mg
Non-Dairy Sources:
Fortified plant milks (1 cup): 300 mg
Tofu made with calcium sulfate (4 oz): 200-400 mg
Canned sardines with bones (3 oz): 325 mg
Canned salmon with bones (3 oz): 180 mg
Leafy greens like kale, collards (1 cup cooked): 100-200 mg
Fortified cereals: varies
Almonds (1/4 cup): 75 mg
Note: Oxalates in spinach and chard reduce calcium absorption from these foods.
Important Considerations
Check Elemental Calcium: Supplement labels show total compound weight, but "elemental calcium" tells you how much actual calcium you're getting.
Balance is Key: More is not always better. Aim for recommended amounts and don't dramatically exceed them without medical supervision.
Monitor Total Intake: Add up calcium from both food and supplements to ensure you're not getting too much.
Age Matters: Absorption efficiency decreases with age. Older adults may need to be more strategic about supplementation.
Pregnancy and Breastfeeding: Requirements are the same as other adults the same age, as the body becomes more efficient at absorbing calcium during these times. Adolescent mothers need more due to their own bone development.
Bottom Line
Calcium is essential for health, but like most nutrients, it's best obtained primarily through a balanced diet, with supplementation used thoughtfully when dietary intake is insufficient. Always consult with a healthcare provider before starting any new supplement regimen, especially if you have existing health conditions or take medications.