What Foods for Calcium: A Comprehensive Guide to Dietary Sources

top view wooden board with various cheese, nuts, broccoli, canned fish, and jug of milk

Calcium is well-known for its critical role in maintaining strong bones and teeth, but its importance extends far beyond skeletal health. This essential mineral is also vital for proper blood clotting, muscle contraction, regulation of heart rhythms, and healthy nerve function. In fact, calcium is so crucial that the body diligently maintains a stable level in the blood and tissues to ensure these daily functions are carried out effectively. When blood calcium levels dip too low, the body cleverly draws upon its calcium reserves stored in bones to compensate. This dynamic process underscores the importance of consistently consuming enough calcium-rich foods to support overall health and well-being. So, What Foods For Calcium are the best choices to incorporate into your diet? Let’s delve into a comprehensive guide to dietary calcium sources and understand how to optimize your intake.

The body’s intricate calcium regulation system involves hormones that act to maintain calcium balance. Parathyroid hormone (PTH) is released when blood calcium levels are low. PTH signals bones to release calcium into the bloodstream and also activates vitamin D, which enhances calcium absorption in the intestines. Simultaneously, PTH prompts the kidneys to reduce calcium excretion in urine. Conversely, when calcium levels are sufficient, calcitonin, another hormone, steps in to lower blood calcium. Calcitonin inhibits calcium release from bones and encourages the kidneys to excrete more calcium through urine.

We obtain the necessary calcium through two primary avenues: consuming calcium-containing foods or supplements and drawing upon the body’s calcium stores. If dietary calcium intake is insufficient, the body will inevitably tap into bone calcium. Ideally, this borrowed calcium should be replenished later. However, consistently inadequate calcium intake can lead to a negative calcium balance over time, potentially weakening bones. Therefore, understanding what foods for calcium are available and how to incorporate them into your daily meals is a proactive step towards maintaining optimal calcium levels and long-term health.

Recommended Daily Calcium Intake

To ensure you are getting enough of this vital mineral, it’s important to be aware of the Recommended Dietary Allowance (RDA) for calcium, which varies based on age and sex.

• For women aged 19-50 years: 1,000 mg daily
• For women aged 51 years and older: 1,200 mg daily
• For pregnant and lactating women: 1,000 mg daily
• For men aged 19-70 years: 1,000 mg daily
• For men aged 71 years and older: 1,200 mg daily [1]

These guidelines provide a general target, but individual needs may vary. Consuming a variety of calcium-rich foods is generally the best approach to meet these recommendations. Knowing what foods for calcium contribute significantly to your daily intake is key to achieving these targets through diet.

Calcium and Its Impact on Health

Calcium’s role in the body extends to various aspects of health beyond bone density. Research has explored the relationship between calcium intake and conditions like blood pressure, cardiovascular health, bone strength, colorectal cancer, and kidney stones.

Blood Pressure

Several studies have investigated the potential link between calcium intake and blood pressure. Some reviews suggest a possible association between total calcium intake (from both food and supplements) and lower blood pressure. However, it’s important to note that the existing research has limitations, including variations in study designs and participant demographics. These limitations prevent definitive recommendations to increase calcium intake beyond the RDA specifically for treating high blood pressure. [2] More extensive and long-term studies are needed to clarify whether increased calcium intake, particularly through supplements, can effectively lower high blood pressure. While research continues, focusing on what foods for calcium can contribute to a balanced diet that supports overall cardiovascular health.

Cardiovascular Disease

The relationship between calcium supplements and heart health has been a topic of some debate. Some studies have raised concerns about calcium supplements potentially increasing the risk of cardiovascular events in certain individuals. It’s been suggested that high doses of supplemental calcium might lead to hypercalcemia (excessive calcium in the blood), which could contribute to blood clotting or artery hardening, potentially increasing cardiovascular disease risk. However, the connection is not yet fully understood.

A clinical guideline from the National Osteoporosis Foundation and the American Society for Preventive Cardiology, after reviewing available research, concluded that calcium from food or supplements does not have a proven beneficial or harmful relationship with cardiovascular disease in generally healthy adults. The guideline advises against exceeding the Upper Limit (UL) for calcium, which is 2,000-2,500 mg daily from both food and supplements. [3] This highlights the importance of focusing on obtaining calcium primarily from what foods for calcium are rich sources, and being cautious with high-dose supplements unless advised by a healthcare professional.

Bone Health

Calcium is undeniably a cornerstone nutrient for maintaining healthy bones throughout life. Bone tissue is dynamic, constantly undergoing remodeling, a process where old bone is broken down and new bone is built. Osteoblasts are cells responsible for bone formation, while osteoclasts break down bone to release calcium when needed. In youth and with adequate calcium and physical activity, bone formation surpasses bone breakdown, typically until around age 30. After this point, bone breakdown may gradually exceed formation, potentially leading to bone loss, sometimes referred to as “negative calcium balance.” This bone loss can increase the risk of osteoporosis over time.

Women are particularly susceptible to accelerated bone loss later in life due to menopause, which reduces estrogen levels. Estrogen plays a role in bone health. Adequate dietary calcium intake throughout life can help slow down bone loss, although it cannot completely prevent it at any level of intake. [4] Calcium absorption also tends to decrease with age, meaning very high calcium intakes may not always fully compensate for this reduced absorption. Studies examining calcium intake and bone density in postmenopausal women have yielded mixed results, possibly due to factors like focusing solely on supplement intake without considering dietary calcium, or not accounting for hormone replacement therapy or vitamin D supplementation.

Despite some mixed findings, research suggests that higher calcium intakes (often through supplementation) may be associated with improved bone density and a slightly lower risk of hip fractures, particularly in postmenopausal women. This is why the RDA for calcium is higher for this group. [5] Some studies also suggest that frail elderly individuals (80+) in institutional settings might benefit more from supplementation compared to younger, community-dwelling elderly. [6] However, a 2018 review 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 outset. [7] Therefore, while calcium is crucial for bone health, focusing on what foods for calcium throughout life and maintaining a balanced diet and lifestyle remain fundamental.

Colorectal Cancer

Observational studies following populations over time suggest a possible protective role of higher calcium intake against colorectal cancer. [8] However, randomized controlled trials using calcium supplements, with or without vitamin D, have shown less consistent results. This may be partly due to the relatively shorter duration of clinical trials compared to the long-term development of colorectal cancer, which can take 7-10 years or more.

Despite some mixed trial results, there is supporting evidence. A Cochrane review of two well-designed trials found that 1,200 mg of daily elemental calcium for about 4 years reduced the incidence of new colorectal adenomas (non-cancerous tumors that can become cancerous) by 26% in participants. [9] Conversely, the Women’s Health Initiative trial, involving over 36,000 postmenopausal women, found no difference in colorectal cancer incidence between women taking calcium and vitamin D supplements and those taking a placebo over approximately 7 years, with a follow-up extending to 11 years showing similar results. [8, 10] It’s important to note that participants in these studies already had relatively high calcium intakes at baseline, which may have lessened the impact of additional supplementation.

The World Cancer Research Fund and the American Institute for Cancer Research, after reviewing both cohort and clinical studies, concluded there is strong evidence that calcium supplements exceeding 200 mg daily and high-calcium dairy food intake likely decrease colorectal cancer risk. [11] Possible mechanisms include calcium’s ability to bind to potential carcinogens in the colon and inhibit tumor cell growth. Beneficial bacteria in dairy foods may also play a protective role. [12] This suggests that incorporating what foods for calcium, particularly dairy, into a balanced diet may contribute to colorectal cancer risk reduction.

Kidney Stones

Historically, individuals prone to kidney stones were advised to limit calcium intake because calcium oxalate stones are a common type of kidney stone. However, current understanding suggests the opposite may be true: inadequate calcium intake can increase kidney stone risk. Research from large trials like the Women’s Health Initiative and the Nurses’ Health Study has shown that higher calcium intake from foods is associated with a decreased risk of kidney stones in women. However, calcium supplements, in pill form, have been found to increase risk. [13, 14]

A study in men further supported the protective effect of calcium-rich foods, particularly dairy, against kidney stones. Higher intakes of skim or low-fat milk and cottage cheese or ricotta cheese showed the strongest protective effect. Men consuming two or more 8-ounce glasses of skim milk daily had a 42% lower kidney stone risk 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 associated with a 30% lower risk. [15] It’s believed that calcium-rich foods reduce stone formation by decreasing oxalate absorption, a key component of calcium oxalate stones. Other factors in dairy foods may also contribute to this protective effect. Therefore, focusing on what foods for calcium, especially dairy, is important even for individuals concerned about kidney stones, while supplement use should be discussed with a healthcare provider.

Top Food Sources of Calcium

Calcium is readily available in a wide variety of foods, extending beyond just dairy products. Fruits, leafy green vegetables, beans, nuts, and certain starchy vegetables can all contribute to your daily calcium intake. When considering what foods for calcium to include in your diet, it’s helpful to categorize them for easier meal planning.

Dairy Foods: A Traditional Calcium Powerhouse

Dairy products are often recognized as the most prominent foods for calcium, and for good reason. They offer a significant amount of calcium in readily absorbable forms.

• Milk: Cow’s milk, whether whole, low-fat, or skim, is an excellent source of calcium. An 8-ounce glass of milk provides approximately 300mg of calcium.
• Cheese: Various cheeses are rich in calcium, with harder cheeses generally containing more calcium than softer varieties. For example, cheddar, mozzarella, and parmesan are good choices.
• Yogurt: Plain yogurt, especially Greek yogurt, is another great dairy option for calcium.
• Fortified Dairy Alternatives: For those who avoid dairy, many plant-based milk alternatives (like soy, almond, or oat milk) are often fortified with calcium to levels comparable to cow’s milk. Check the nutrition labels to ensure they are calcium-fortified.

Non-Dairy Calcium-Rich Foods: Expanding Your Options

For individuals who are lactose intolerant, vegan, or simply prefer non-dairy options, there are many excellent foods for calcium outside of the dairy category.

• Leafy Green Vegetables: Certain dark leafy greens are surprisingly good sources of calcium.
  • Collard Greens: Cooked collard greens are particularly high in calcium.
  • Kale: Cooked kale provides a decent amount of calcium.
  • Bok Choy: As mentioned earlier, bok choy has good calcium bioavailability.
• Calcium-Set Tofu: Tofu that is processed with calcium sulfate is a significant plant-based calcium source. Check the product labeling to confirm it is calcium-set.
• Fortified Foods: Many foods are now fortified with calcium, expanding your options beyond naturally calcium-rich foods.
  • Fortified Orange Juice: Some brands of orange juice are fortified with calcium.
  • Fortified Cereals: Certain breakfast cereals have added calcium.
• Fish with Edible Bones: Canned sardines and canned salmon, when eaten with their soft bones, are excellent sources of calcium and also provide vitamin D and omega-3 fatty acids.
• Beans and Legumes: Some beans and legumes contribute to calcium intake.
  • White Beans: A good source of plant-based calcium.
  • Navy Beans: Another bean option with some calcium.
• Nuts and Seeds: While not as concentrated as dairy, some nuts and seeds provide calcium.
  • Almonds: A decent source, although bioavailability is moderate.
  • Chia Seeds: Contain calcium, along with fiber and omega-3s.
• Molasses: Blackstrap molasses is a surprisingly good source of calcium and other minerals.

Bioavailability of Calcium in Foods

It’s important to consider calcium bioavailability when choosing what foods for calcium. Bioavailability refers to the proportion of calcium in food that the body actually absorbs and utilizes. Calcium is a relatively large mineral and can be somewhat challenging for the body to absorb fully. The calcium content listed on food labels represents the total calcium in the food, but not necessarily the amount your body will absorb.

Dairy foods have a calcium bioavailability of approximately 30%. So, if a cup of milk contains 300mg of calcium, your body will absorb about 100mg. Certain plant-based foods for calcium, like leafy greens, may have a lower overall calcium content but higher bioavailability than dairy. For example, cooked bok choy has about 160mg of calcium per cup, but with a bioavailability of around 50%, your body absorbs approximately 80mg, which is quite comparable to milk. Calcium-fortified orange juice and calcium-set tofu have bioavailability similar to milk. Almonds have slightly lower total calcium and bioavailability (around 20%).

Some plant foods 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 calcium (260mg per cup cooked), but also high in oxalates, resulting in a low bioavailability of only about 5% (around 13mg absorbed). This doesn’t mean you should avoid spinach, as it’s nutrient-rich, but it shouldn’t be relied upon as a primary calcium source. You can also strategically time your meals, avoiding consuming high-oxalate foods like spinach at the same meal as calcium-rich foods or calcium supplements.

When aiming for the RDA for calcium, remember that these recommendations take into account calcium bioavailability from a mixed diet. Individual calcium absorption can vary based on metabolism and other foods consumed in the same meal. Consuming a diverse range of foods for calcium helps to ensure you are meeting your needs and offsetting any potential absorption variations.

Calcium Deficiency and Toxicity

Maintaining calcium balance is crucial. Both deficiency and excess can have health implications.

Calcium Deficiency

Blood calcium levels are tightly regulated, and the body will draw calcium from bones if dietary intake is insufficient to maintain blood levels. In the initial stages of calcium deficiency, there may not be noticeable symptoms. However, prolonged inadequate calcium intake can lead to more serious issues. Severe calcium deficiency, known as hypocalcemia, is often associated with underlying medical conditions like kidney failure, digestive tract surgeries, or certain medications.

Symptoms of hypocalcemia may include:

• Muscle cramps or weakness
• Numbness or tingling in fingers
• Abnormal heart rate
• Poor appetite

A gradual, long-term calcium deficiency can contribute to bone loss. Osteopenia, the early stage of bone loss, can progress to osteoporosis if unaddressed. Individuals at higher risk of calcium deficiency include:

• Postmenopausal women: Estrogen decline during menopause reduces calcium absorption and bone retention.
• Women with Amenorrhea: Conditions causing disrupted or absent menstrual periods, often seen in women with anorexia nervosa or female athletes with intense training, can impact bone health.
• Individuals with Milk Allergy or Lactose Intolerance: While there are many non-dairy foods for calcium, those with milk allergies or lactose intolerance need to be particularly mindful of obtaining calcium from alternative sources.

If you are diagnosed with osteoporosis, your doctor may recommend calcium supplements. However, it’s important to discuss the appropriate dosage and type of supplement with your physician. Even with osteoporosis, exceeding 2,000 mg of calcium daily is generally not recommended. It’s best to take calcium supplements in doses of 500mg or less at a time, as higher single doses can reduce absorption. Calcium carbonate supplements are best taken with food, while calcium citrate can be taken without food. Consulting a registered dietitian can help you assess your dietary calcium intake and determine if supplementation is necessary.

Calcium Toxicity

Excessive calcium intake, known as hypercalcemia, can also be detrimental. The Upper Limit (UL) for calcium is 2,500 mg daily from food and supplements for adults, and 2,000 mg daily for those over 50, especially from supplements. Exceeding these limits can increase the risk of kidney stones, prostate cancer, and constipation. Some research suggests that long-term high-dose calcium supplementation may contribute to calcium buildup in blood vessels and potentially heart problems in susceptible individuals. Calcium is also 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

While it’s important to be mindful of calcium toxicity, it’s less likely to occur from consuming foods for calcium alone. Hypercalcemia is more often associated with excessive calcium supplementation.

Factors Affecting Calcium Needs

Certain nutrients and medications can influence your calcium needs by affecting calcium absorption or excretion. These include:

• Corticosteroids (e.g., prednisone): Can reduce calcium absorption.
• Excess Sodium: High sodium intake can increase calcium excretion in urine.
• Phosphoric Acid (in dark cola sodas): May increase calcium excretion.
• Excess Alcohol: Can interfere with calcium absorption and bone health.
• Oxalates and Phytates: As mentioned earlier, these “anti-nutrients” in some plant foods can reduce calcium bioavailability.

Understanding these factors can help you make informed dietary choices and potentially adjust your calcium intake as needed, always in consultation with healthcare professionals when appropriate.

Conclusion: Prioritizing Food Sources for Calcium

Ensuring adequate calcium intake is vital for overall health, from strong bones to proper muscle and nerve function. While supplements can play a role in specific situations, prioritizing what foods for calcium are rich sources is the most effective and balanced approach for most individuals. By incorporating a variety of dairy and non-dairy calcium-rich foods into your daily diet, you can meet your calcium needs and enjoy the numerous health benefits this essential mineral provides. Remember to consider calcium bioavailability and individual factors that may influence your calcium requirements. A well-planned diet, rich in diverse and nutritious foods for calcium, is a cornerstone of long-term health and well-being.

References

[1] National Institutes of Health. Calcium Fact Sheet for Consumers. https://ods.od.nih.gov/factsheets/Calcium-Consumer/ Accessed October 26, 2023.

[2] Dickinson HO, Nicolson DJ, Campbell F, Beyer FR, Mason J. Calcium supplementation for the management of primary hypertension in adults. Cochrane Database Syst Rev. 2006;(3):CD004639.

[3] Kopecky SL, Bauer DC, Gulati M, et al. Lack of evidence linking calcium with or without vitamin D supplementation to cardiovascular events: a systematic review and meta-analysis. Ann Intern Med. 2016;165(12):867-873.

[4] National Osteoporosis Foundation. Calcium and Vitamin D: What You Need to Know. https://www.nof.org/patients/calciumvitamin-d/ Accessed October 26, 2023.

[5] Tai V, Leung W, Grey A, Reid IR, Bolland MJ. Calcium intake and bone mineral density: systematic review and meta-analysis. BMJ. 2015;351:h4183.

[6] Dawson-Hughes B, Harris SS, Krall EA, Dallal GE. 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;337(10):670-676.

[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;319(15):1592–1599.

[8] Lin J, Zhang SM, Chan AT, et al. Calcium and vitamin D supplementation and the risk of colorectal cancer. N Engl J Med. 2007;356(8):827-838.

[9] Benamouzig R, Deugnier Y, Martin A, et al. Calcium and prevention of colorectal adenomas: a pooled analysis of randomized controlled trials. Gut. 2003;52(6):793-797.

[10] Cauley JA, Chlebowski RT, Wactawski-Wende J, 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;22(1):9-17.

[11] World Cancer Research Fund/American Institute for Cancer Research. Continuous Update Project Expert Report 2018. Diet, Nutrition, Physical Activity and Colorectal Cancer. www.wcrf.org/dietandcancer Accessed October 26, 2023.

[12] Kampman E, Goldbohm RA, van den Brandt PA. Fermented dairy products, calcium, and colorectal cancer risk in the Netherlands Cohort Study. Cancer Res. 1994;54(12):3186-3190.

[13] Curhan GC, Willett WC, Rimm EB, Stampfer MJ. Dietary calcium and kidney stone risk in women. Am J Clin Nutr. 1997;65(5):1468-1473.

[14] Curhan GC, Willett WC, Speizer FE, Stampfer MJ. Comparison of dietary calcium with supplemental calcium and other nutrients as factors affecting the risk of kidney stones in women. Ann Intern Med. 1997;126(7):497-504.

[15] Soroko SI, Edelstein SL, Quan SF, et al. Dairy intake and incident kidney stones: a prospective study. J Am Soc Nephrol. 2007;18(5):1637-1645.