Calcium is an essential mineral, renowned for its critical role in maintaining strong bones and healthy teeth. Beyond these well-known benefits, calcium is also vital for blood clotting, muscle contraction, regulating heart rhythms, and nerve function. Approximately 99% of the body’s calcium is stored in the bones, while the remaining 1% circulates in the blood, muscles, and other tissues, highlighting its systemic importance.
The body diligently maintains a stable level of calcium in the blood to support these crucial daily functions. When blood calcium levels dip too low, the parathyroid hormone (PTH) signals the bones to release calcium into the bloodstream. PTH also activates vitamin D, enhancing calcium absorption in the intestines, and instructs the kidneys to reduce calcium excretion in urine. Conversely, when calcium levels are sufficient, calcitonin, another hormone, works to lower blood calcium by inhibiting calcium release from bones and prompting the kidneys to eliminate more calcium through urine.
To ensure it has enough calcium, the body relies on two primary sources: consuming foods or supplements rich in calcium and drawing from its calcium reserves in the body, mainly the bones. Insufficient intake of Foods Containing Calcium compels the body to borrow calcium from bones. Ideally, this borrowed calcium should be replenished, but this isn’t always guaranteed, even with increased calcium consumption later on.
top view wooden board with various cheese, nuts, broccoli, canned fish, and jug of milk
Recommended Daily Calcium Intake
Adequate calcium intake is crucial for overall health, and the recommended daily amounts vary based on age and gender. The Recommended Dietary Allowance (RDA) for calcium is as follows:
- Women (19-50 years): 1,000 mg daily
- Women (51+ years): 1,200 mg daily
- Pregnant and Lactating Women: 1,000 mg daily
- Men (19-70 years): 1,000 mg daily
- Men (71+ years): 1,200 mg daily [1]
These recommendations are designed to help most healthy individuals maintain sufficient calcium levels for optimal bodily functions and bone health.
The Health Benefits of Calcium-Rich Foods
Numerous studies have investigated the impact of calcium, primarily from foods containing calcium, on various health conditions. Here’s a closer look at the evidence:
Blood Pressure
Several reviews analyzing the relationship between total calcium intake (from both food and supplements) and blood pressure suggest a potential link between calcium and lower blood pressure. However, due to limitations in study designs, such as small participant groups, variations among study populations, and inherent biases in the types of studies reviewed, there isn’t enough evidence to recommend increasing calcium intake beyond the RDA specifically for treating high blood pressure. [2] More extensive and longer-term research is needed to definitively determine if increased calcium intake, whether through diet or supplements, can effectively lower high blood pressure.
Cardiovascular Health
Some research has raised concerns regarding calcium supplements and their potential impact on heart health. These studies indicate that calcium supplements might increase the risk of cardiovascular events in both men and women. It’s hypothesized that high doses of supplemental calcium could lead to hypercalcemia (excessive calcium in the blood), potentially causing blood clots or artery hardening, thus increasing cardiovascular disease risk. While the connection is still under investigation, a clinical guideline from the National Osteoporosis Foundation and the American Society for Preventive Cardiology, based on a review of existing research, concludes that calcium from foods containing calcium or supplements shows no clear relationship (neither beneficial nor harmful) with cardiovascular disease in generally healthy adults. The guideline advises against exceeding the Upper Limit for calcium intake, which is 2,000-2,500 mg daily from both food and supplements. [3] Focusing on obtaining calcium from foods containing calcium as part of a balanced diet is generally recommended over high-dose supplementation.
Bone Health
Calcium is undeniably a cornerstone nutrient for bone health. Bone tissue is dynamic, constantly undergoing remodeling – a process where old bone is broken down and new bone is built. Osteoblasts are bone cells responsible for building bone, while osteoclasts break down bone when calcium is needed elsewhere in the body. In healthy individuals with sufficient calcium intake and regular physical activity, bone formation surpasses bone breakdown until around age 30. After this point, bone breakdown typically exceeds formation, leading to a “negative calcium balance” and potential bone loss. Women are particularly susceptible to accelerated bone loss later in life due to menopause, which reduces hormone levels crucial for bone building and maintenance. Adequate dietary calcium throughout life can help slow bone loss, although it cannot entirely prevent it. [4] Calcium absorption efficiency decreases with age, meaning very high calcium intakes may not always resolve age-related bone loss issues. Studies on calcium intake and bone density in postmenopausal women have yielded mixed results, potentially due to factors like only assessing supplement calcium intake without considering dietary sources, or not accounting for hormone replacement therapy or other vitamin supplements like vitamin D that influence bone health.
However, some large trials have shown that higher calcium intakes, often achieved through supplementation, are linked to improved bone density and a slightly reduced risk of hip fractures. This is why the RDA for calcium is higher for postmenopausal women than for younger women. [5] Some research suggests that frail elderly individuals (80+ years in institutional care) might benefit more from supplementation than younger, community-dwelling elderly. [6] Conversely, a 2018 review of randomized controlled trials by the U.S. Preventive Services Task Force found that calcium and vitamin D supplements taken for up to 7 years did not reduce fracture incidence in postmenopausal women without osteoporosis or vitamin D deficiency at the study’s start. Supplement dosages in these studies ranged from 600-1,600 mg of calcium daily. [7] These findings underscore the complexity of calcium’s role in bone health and suggest that focusing on foods containing calcium and maintaining adequate vitamin D levels alongside a healthy lifestyle may be more beneficial for long-term bone health than relying solely on supplements, especially for generally healthy postmenopausal women.
Colorectal Cancer
Epidemiological studies following populations over time suggest a protective effect of high calcium intake, from both foods containing calcium and supplements, against colorectal cancer. [8] However, randomized controlled trials specifically using calcium supplements, with or without vitamin D, have produced inconsistent results, possibly due to the relatively short duration of these trials compared to the long development time of colorectal cancer (7-10 years or more).
- A Cochrane review of two well-designed, double-blind, placebo-controlled trials found that daily intake of 1,200 mg of elemental calcium for approximately 4 years reduced the incidence of new colorectal adenomas (non-cancerous tumors that can become cancerous) by 26% in participants, some of whom had a history of adenomas. [9]
- In contrast, a randomized double-blind placebo-controlled trial from the Women’s Health Initiative, involving 36,282 postmenopausal women, administered 500 mg elemental calcium and 200 IU vitamin D twice daily, or a placebo, for about 7 years. This trial found no significant difference in colorectal cancer incidence between the two groups. [8] A five-year follow-up study (total 11-year follow-up) also showed no reduced colorectal cancer incidence with the same calcium and vitamin D supplement regimen. [10] These studies noted that the participants already had a high baseline calcium intake, potentially diminishing the impact of additional supplements.
Despite these mixed findings, a review by the World Cancer Research Fund and the American Institute for Cancer Research, analyzing both cohort and clinical studies, reported strong evidence that calcium supplements exceeding 200 mg daily and high-calcium dairy foods containing calcium likely decrease colorectal cancer risk. [11] Potential mechanisms include calcium’s ability to bind to toxic substances in the colon and inhibit tumor cell growth. Certain bacteria in dairy foods containing calcium may also offer protection against cancerous cell development in the colon. [12] This suggests that prioritizing foods containing calcium, particularly dairy, may contribute to colorectal cancer prevention.
Kidney Stones
Contrary to previous recommendations that kidney stone patients should limit calcium intake, current understanding indicates that inadequate intake of foods containing calcium can actually increase the risk of kidney stone formation, specifically calcium-oxalate stones, the most common type. Research from large trials like the Women’s Health Initiative and the Nurses’ Health Study has shown that higher intake of calcium from foods containing calcium is associated with a decreased risk of kidney stones in women. However, this protective effect is not observed with calcium supplements, which have been found to increase kidney stone risk. [13, 14] A study in a cohort of 45,619 men also found that calcium-rich foods containing calcium, mainly dairy, offered protection against kidney stones. Skim or low-fat milk and cottage cheese or ricotta cheese showed the most significant protective effects. Men consuming two or more 8-ounce glasses of skim milk daily had a 42% lower risk of developing kidney stones compared to those drinking less than one glass a month. Similarly, eating two or more half-cup servings of cottage cheese or ricotta cheese weekly was linked to a 30% reduced risk compared to less than one serving a month. [15] It’s believed that calcium from foods containing calcium reduces stone formation by decreasing oxalate absorption, a key component of calcium-oxalate stones. Other components in dairy foods containing calcium may also contribute to this protective effect. Therefore, choosing foods containing calcium is a preferable strategy for kidney stone prevention compared to supplementation.
Top Food Sources of Calcium
Calcium is widely available in numerous foods containing calcium, extending beyond just milk and dairy products. A diverse range of options, including fruits, leafy greens, beans, nuts, and certain starchy vegetables, are excellent sources.
Here are some of the top foods containing calcium to incorporate into your diet:
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Dairy Products: Milk, yogurt, and cheese are well-known and rich sources of calcium. Opt for low-fat or fat-free versions to manage calorie intake while maximizing calcium benefits.
- Milk: Cow’s milk is a classic source, providing around 300mg of calcium per cup.
- Yogurt: Plain yogurt, especially Greek yogurt, is packed with calcium and probiotics.
- Cheese: Hard cheeses like cheddar, parmesan, and mozzarella are high in calcium.
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Non-Dairy Alternatives: For those who are lactose intolerant or follow a vegan diet, many plant-based alternatives are fortified with calcium.
- Fortified Plant Milks: Almond milk, soy milk, oat milk, and other plant-based milks are often fortified with calcium, vitamin D, and vitamin B12. Check labels to ensure adequate calcium content, aiming for options with at least 300mg of calcium per cup, similar to cow’s milk.
- Calcium-Set Tofu: Tofu processed with calcium sulfate is a good source of calcium.
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Leafy Green Vegetables: Certain leafy greens offer a significant amount of bioavailable calcium.
- Kale: Cooked kale is a good source of calcium.
- Collard Greens: Another excellent leafy green source of calcium.
- Bok Choy: Offers a high bioavailability of calcium, meaning a good portion of its calcium content is absorbed by the body.
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Nuts and Seeds: Certain nuts and seeds contribute to daily calcium intake.
- Almonds: Almonds are a decent source of calcium, and almond butter also provides calcium.
- Sesame Seeds: Sesame seeds and tahini (sesame seed paste) are calcium-rich.
- Chia Seeds: Chia seeds contain a notable amount of calcium, along with fiber and omega-3 fatty acids.
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Fish with Edible Bones: Canned fish where you consume the bones are excellent sources of calcium.
- Sardines: Canned sardines with bones are very high in calcium and omega-3 fatty acids.
- Canned Salmon: Canned salmon with bones is another good source of calcium and omega-3s.
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Beans and Legumes: Some beans and legumes contribute to calcium intake.
- White Beans: Provide a good amount of calcium.
- Kidney Beans: Offer a moderate amount of calcium.
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Fruits: While fruits are not as calcium-dense as other food groups, some contribute to calcium intake.
- Figs: Dried figs are a source of calcium and fiber.
- Oranges: Oranges contain a small amount of calcium, and fortified orange juice is also available.
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Fortified Foods: Many processed foods are fortified with calcium to increase their nutritional value.
- Fortified Cereals: Ready-to-eat cereals are often fortified with calcium and other vitamins and minerals.
- Fortified Breads and Grains: Some breads and grain products are fortified with calcium.
Bioavailability of Calcium in Foods
It’s important to understand calcium bioavailability – the proportion of calcium in food that the body actually absorbs and utilizes. Calcium is a large mineral, and its absorption in the gut isn’t always straightforward. The calcium amount listed on food labels represents the total calcium content but not necessarily the amount absorbed.
Dairy foods containing calcium have a bioavailability of approximately 30%. For instance, if a cup of milk contains 300mg of calcium, about 100mg will be absorbed. Plant-based foods containing calcium like leafy greens may have less total calcium but often exhibit higher bioavailability than dairy. Bok choy, for example, contains about 160mg of calcium per cooked cup with a 50% bioavailability, meaning roughly 80mg is absorbed – nearly as much bioavailable calcium as a cup of milk. Calcium-fortified orange juice and calcium-set tofu have bioavailability similar to milk, while almonds have slightly lower total calcium and about 20% bioavailability.
However, some plant foods containing calcium contain naturally occurring compounds called “anti-nutrients,” such as oxalates and phytates, which can bind to calcium and reduce its bioavailability. Spinach, for example, is high in total calcium (260mg per cooked cup) but also high in oxalates, resulting in a low bioavailability of only about 5% (approximately 13mg absorbed). This doesn’t mean avoiding spinach, as it’s nutrient-rich, but it shouldn’t be relied upon as a primary calcium source. Meal timing can also influence calcium absorption; avoid consuming “calcium-binding” foods like spinach simultaneously with calcium-rich foods containing calcium or calcium supplements.
When aiming for the RDAs for calcium, remember that these recommendations consider calcium bioavailability in food. Individual calcium absorption can vary based on metabolism and other foods consumed in the same meal. Consuming a variety of foods containing calcium helps to compensate for slight variations in absorption.
Signs of Calcium Deficiency and Toxicity
Calcium Deficiency (Hypocalcemia)
Blood calcium levels are tightly regulated, and the body will draw calcium from bones if dietary intake is insufficient to maintain normal blood levels. In many cases, early-stage calcium deficiency doesn’t present obvious symptoms. However, severe or prolonged calcium deficiency, known as hypocalcemia, can arise from conditions like kidney failure, digestive tract surgeries (e.g., gastric bypass), or medications like diuretics that interfere with calcium absorption.
Symptoms of hypocalcemia may include:
- Muscle cramps or weakness
- Numbness or tingling in fingers
- Abnormal heart rate
- Poor appetite
A gradual calcium deficiency over time can occur in individuals with chronically low dietary calcium intake or impaired calcium absorption. Osteopenia, the initial stage of bone loss, can progress to osteoporosis if untreated. Individuals at higher risk of calcium deficiency include:
- Postmenopausal women: Menopause-related estrogen decline reduces calcium absorption and bone retention. Hormone replacement therapy (HRT) may be prescribed to prevent osteoporosis in some cases.
- Amenorrhea: Disruption or cessation of menstrual periods, often seen in young women with anorexia nervosa or female athletes with intense training regimens, can impair calcium absorption and bone health.
- Milk allergy or lactose intolerance: These conditions can limit dairy consumption, a major source of calcium, increasing the risk of deficiency if alternative foods containing calcium are not adequately incorporated into the diet.
Guidelines for Calcium Supplements in Osteoporosis: If diagnosed with osteoporosis, your physician may recommend over-the-counter calcium supplements. If so, consider these points:
- Clarify total daily calcium needs: Discuss with your doctor the total calcium intake required daily, including both food and supplements. Even with osteoporosis, exceeding 2,000 mg daily is generally not recommended due to potential health risks. It is generally not recommended to exceed 1,200 mg daily, even with an osteoporosis diagnosis.
- Divide supplement doses: Taking large doses of calcium supplements at once can actually reduce absorption. It’s best to take no more than 500 mg of calcium at a time. For higher prescribed doses, divide them throughout the day, with at least 4 hours between doses.
- Choose supplement type: Calcium carbonate and calcium citrate are common supplement forms. Calcium carbonate is best taken with food as it requires stomach acid for absorption, while calcium citrate can be taken without food.
- Consult a dietitian: If unsure about dietary calcium intake, consult a registered dietitian. They can help estimate your dietary calcium intake, allowing you to calculate the necessary supplemental calcium to reach your recommended total daily intake. Inform your doctor about a very high calcium diet (e.g., high dairy consumption) so they can factor it into your calcium prescription.
Calcium Toxicity (Hypercalcemia)
Excessive calcium in the blood is termed hypercalcemia. The Upper Limit (UL) for calcium is 2,500 mg daily from foods containing calcium and supplements combined. For individuals over 50, the UL is often recommended to be lower, around 2,000 mg daily, especially from supplements, due to increased risk of kidney stones, prostate cancer, and constipation at higher intakes. Some research suggests that long-term high-dose calcium supplementation might contribute to calcium accumulation in blood vessels and increase heart problems in susceptible individuals. Furthermore, calcium is a large mineral that can interfere with the absorption of other minerals like iron and zinc.
Symptoms of hypercalcemia may include:
- Weakness, fatigue
- Nausea, vomiting
- Shortness of breath
- Chest pain
- Heart palpitations, irregular heart rate
Did You Know?
Certain nutrients and medications can increase your calcium needs by reducing calcium absorption or increasing calcium excretion. These include corticosteroids (e.g., prednisone), high sodium intake, phosphoric acid (found in dark cola sodas), excessive alcohol consumption, and oxalates (as discussed in “Are anti-nutrients harmful?”).
Related Resources
Vitamins and Minerals
References
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[2] Cappuccio FP, et al. Calcium supplementation and blood pressure: a systematic review and meta-analysis. J Hypertens. 2006 Dec;24(12):1701-11.
[3] Chung M, et al. Vitamin D and Calcium: A Systematic Review of Health Outcomes [Internet]. Rockville (MD): Agency for Healthcare Research and Quality (US); 2009 Aug. (Evidence Reports/Technology Assessments, No. 183.) Available from: http://www.ncbi.nlm.nih.gov/books/NBK38539/
[4] Dawson-Hughes B, et al. Effect of calcium and vitamin D supplementation on bone density in men and women 65 years of age or older. N Engl J Med. 1997 Jul 3;337(2):67-74.
[5] Shea B, et al. Calcium supplementation on bone loss in postmenopausal women. Cochrane Database Syst Rev. 2011 Aug 10;(8):CD004526.
[6] Chapuy MC, et al. Vitamin D3 and calcium to prevent hip fractures in elderly women. N Engl J Med. 1992 Dec 3;327(23):1637-42.
[7] U.S. Preventive Services Task Force. Vitamin D and Calcium Supplementation to Prevent Fractures: U.S. Preventive Services Task Force Recommendation Statement. JAMA. 2018 Feb 20;319(6):598-609.
[8] Lin J, et al. Calcium and vitamin D supplementation and risk of colorectal cancer in women. J Natl Cancer Inst. 2007 Feb 21;99(3):159-71.
[9] Benamouzig R, et al. Calcium intake and colorectal adenoma recurrence: a randomized, double-blind, placebo-controlled trial. Int J Cancer. 2003 Feb 1;103(2):260-2.
[10] Cauley JA, et al. Calcium plus vitamin D supplementation and health outcomes five years after active intervention ended: the Women’s Health Initiative randomized controlled trial. J Womens Health (Larchmt). 2013 Feb;22(2):125-34.
[11] World Cancer Research Fund / American Institute for Cancer Research. Food, Nutrition, Physical Activity, and the Prevention of Cancer: a Global Perspective. Washington DC: AICR, 2007.
[12] Larsson SC, et al. Dairy foods and risk of colorectal cancer: a systematic review and meta-analysis of prospective studies. Am J Clin Nutr. 2004 Jan;79(1):16-25.
[13] Curhan GC, et al. Comparison of dietary calcium with supplemental calcium and other nutrients as factors affecting the risk of kidney stones in women. Ann Intern Med. 1997 Apr 1;126(7):497-504.
[14] Jackson RD, et al. Calcium plus vitamin D supplementation and the risk of fractures. N Engl J Med. 2006 Feb 16;354(7):669-83.
[15] Curhan GC, et al. Dietary dairy and calcium and incident kidney stones in men: a prospective study. J Am Soc Nephrol. 2001 Jun;12(6):1319-25.
