Calcium is well-recognized for its vital role in maintaining strong bones and healthy teeth. However, its importance extends far beyond skeletal health, playing a crucial part in blood clotting, muscle function, nerve signal transmission, and regulating your heartbeat. While 99% of the body’s calcium is stored in bones, the remaining 1% circulates in the blood and soft tissues, underscoring its dynamic role in daily bodily functions. Ensuring you consume adequate Calcium Food Sources is essential for overall well-being and preventing deficiencies that can impact various aspects of health.
Understanding Calcium’s Role and Regulation
Your body diligently maintains a consistent level of calcium in the bloodstream to support these critical functions. When blood calcium levels dip, the parathyroid hormone (PTH) acts as a signal, prompting your bones to release calcium. PTH also activates vitamin D, which is crucial for enhancing calcium absorption in the intestines. Simultaneously, the kidneys are signaled to reduce calcium excretion through urine. Conversely, when calcium levels are sufficient, calcitonin, another hormone, works to decrease blood calcium by inhibiting calcium release from bones and encouraging the kidneys to eliminate more calcium in urine.
The body obtains calcium through two primary methods: consuming calcium-rich foods or supplements, and drawing upon its calcium reserves in the bones. Insufficient intake of calcium food sources leads the body to borrow calcium from bones. Ideally, this borrowed calcium is replenished later, but this doesn’t always occur efficiently, and simply increasing calcium intake may not fully rectify the deficit. Therefore, prioritizing calcium food sources in your daily diet is a proactive approach to maintaining healthy calcium balance.
Recommended Daily Calcium Intake
The recommended dietary allowance (RDA) for calcium varies based on age and gender. For women aged 19-50, the RDA is 1,000 mg daily, increasing to 1,200 mg for women 51 and older. Pregnant and breastfeeding women require 1,000 mg of calcium daily. Men aged 19-70 need 1,000 mg, while men over 71 should aim for 1,200 mg daily. Meeting these recommendations through calcium food sources is a cornerstone of long-term health.
Calcium and its Impact on Health Conditions
Blood Pressure
Numerous studies have explored the relationship between calcium intake and blood pressure. Some research suggests a potential link between adequate calcium consumption, from both food and supplements, and lower blood pressure levels. However, due to inconsistencies in study designs, participant diversity, and potential biases, current evidence is not strong enough to recommend increasing calcium intake beyond the RDA solely for treating high blood pressure. Further research with larger, long-term trials is needed to definitively establish whether increased calcium intake or calcium supplements can effectively lower high blood pressure. Including calcium food sources as part of a balanced diet is still advisable for overall health.
Cardiovascular Health
The relationship between calcium supplements and heart health has been a subject of debate. Some studies have raised concerns about calcium supplements increasing the risk of cardiovascular events, potentially due to high doses leading to hypercalcemia (excessive calcium in the blood). Hypercalcemia might contribute to blood clotting or artery hardening. However, a comprehensive review by the National Osteoporosis Foundation and the American Society for Preventive Cardiology concluded that calcium from food or supplements has no proven beneficial or harmful effect on cardiovascular disease in generally healthy adults. The guideline advises against exceeding the upper limit of 2,000-2,500 mg of calcium daily from all sources. Focusing on calcium food sources rather than relying solely on high-dose supplements is a prudent approach.
Bone Health: The Cornerstone of Calcium’s Benefit
Calcium is undeniably essential for bone health. Bone is a dynamic tissue constantly undergoing remodeling, a process involving bone breakdown and rebuilding. Osteoblasts are cells responsible for building bone, while osteoclasts break down bone when calcium is needed elsewhere in the body. In youth and with sufficient calcium intake and physical activity, bone formation surpasses bone breakdown until around age 30. After this point, bone breakdown typically exceeds formation, leading to potential bone loss, sometimes termed “negative calcium balance.” Adequate dietary calcium intake throughout life, obtained from calcium food sources, can help slow down bone loss, although it cannot entirely prevent it. Calcium absorption tends to decrease with age, making very high calcium intakes less effective at preventing bone loss in older adults. Studies examining calcium intake and bone density in postmenopausal women have yielded varied results, possibly due to factors like not accounting for dietary calcium in supplement studies or not considering hormone replacement therapy or vitamin D supplementation. Despite mixed results, some large trials have shown that higher calcium intakes, often through supplementation, are linked to improved bone density and a slightly reduced risk of hip fractures, leading to a higher RDA for calcium in postmenopausal women. However, a 2018 review of randomized controlled trials found that calcium and vitamin D supplements did not reduce fracture incidence in healthy postmenopausal women without osteoporosis or vitamin D deficiency. Prioritizing calcium food sources alongside vitamin D and weight-bearing exercise remains crucial for maintaining bone health across the lifespan.
Colorectal Cancer
Epidemiological studies suggest a potential protective role of high calcium intake, from both food and supplements, against colorectal cancer. However, randomized controlled trials using calcium supplements have shown inconsistent results, possibly due to the relatively short duration of these trials compared to the long development time of colorectal cancer. A Cochrane review of two trials found that 1,200 mg of daily calcium supplementation reduced the incidence of new colorectal adenomas (non-cancerous tumors) by 26%. Conversely, a large trial from the Women’s Health Initiative found no difference in colorectal cancer incidence with calcium and vitamin D supplementation. However, a review by the World Cancer Research Fund and the American Institute for Cancer Research concluded there is strong evidence that calcium supplements (over 200 mg daily) and high-calcium dairy foods likely decrease colorectal cancer risk. This may be due to calcium’s ability to bind to toxic substances in the colon and inhibit tumor cell growth, or potentially due to beneficial bacteria in dairy foods. Including a variety of calcium food sources, particularly dairy, in a balanced diet may contribute to colorectal cancer risk reduction.
Kidney Stones
Contrary to older recommendations, current research indicates that limiting calcium intake may increase the risk of kidney stones, specifically calcium-oxalate stones, the most common type. Studies have shown that higher intakes of calcium from calcium food sources are associated with a decreased risk of kidney stones in women and men. However, calcium supplements, in pill form, have been found to increase kidney stone risk. Calcium-rich foods, especially dairy, are believed to reduce stone formation by lowering oxalate absorption. Skim or low-fat milk and certain cheeses like cottage cheese and ricotta have shown the strongest protective effect. For example, men consuming two or more glasses of skim milk daily had a significantly lower risk of kidney stones compared to those drinking less than one glass a month. Choosing calcium food sources, particularly dairy, as part of a balanced diet is beneficial for kidney stone prevention.
Key Calcium Food Sources
Calcium is widely available in a variety of foods, beyond just milk and dairy products. Fruits, leafy green vegetables, beans, nuts, and some starchy vegetables are also valuable calcium food sources.
top view wooden board with various cheese, nuts, broccoli, canned fish, and jug of milk
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. While food labels list the total calcium content, bioavailability varies across different calcium food sources. Dairy products have about 30% calcium bioavailability. For instance, a cup of milk with 300 mg of calcium provides approximately 100 mg of absorbable calcium. Plant-based calcium food sources like leafy greens may contain less total calcium but often have higher bioavailability than dairy. Bok choy, for example, has around 160 mg of calcium per cooked cup with a 50% bioavailability, yielding about 80 mg of absorbable calcium, nearly as much as milk. Calcium-fortified orange juice and calcium-set tofu have similar calcium content and bioavailability to milk. Almonds have slightly lower total calcium and a bioavailability of about 20%. This information is particularly relevant for individuals who are lactose intolerant or follow a vegan diet, seeking non-dairy calcium food sources.
Some plant-based calcium food sources contain “anti-nutrients” like oxalates and phytates, which can bind to calcium and reduce its bioavailability. Spinach, while rich in calcium (260 mg per cooked cup), is also high in oxalates, resulting in a low bioavailability of only about 5% (around 13 mg absorbable calcium). While spinach is nutritious, it shouldn’t be relied upon as a primary calcium food source. Timing meals to avoid consuming calcium-binding foods like spinach simultaneously with calcium-rich foods or supplements can improve calcium absorption. When aiming for the RDA for calcium, remember that these recommendations account for bioavailability. Individual calcium absorption can vary based on metabolism and the combination of foods consumed in a meal. Consuming a variety of calcium food sources helps to ensure adequate calcium intake despite variations in bioavailability.
Recognizing Calcium Deficiency and Toxicity
Calcium Deficiency (Hypocalcemia)
Blood calcium levels are tightly regulated, and the body will draw calcium from bones to maintain these levels if dietary intake from calcium food sources is insufficient. Therefore, noticeable symptoms of deficiency are uncommon in early stages. Severe calcium deficiency, or hypocalcemia, typically arises from underlying health conditions like kidney failure, digestive tract surgeries, or medications like diuretics.
Symptoms of hypocalcemia may include:
- Muscle cramps or weakness
- Numbness or tingling in fingers
- Abnormal heart rate
- Poor appetite
Long-term, gradual calcium deficiency, often due to inadequate dietary calcium food sources or impaired calcium absorption, can lead to osteopenia (early bone loss) and eventually osteoporosis. Individuals at higher risk of calcium deficiency include:
- Postmenopausal women: Reduced estrogen levels after menopause decrease calcium absorption and bone retention.
- Amenorrhea: Disrupted or absent menstrual periods, common in women with anorexia nervosa or athletes with extreme training regimens, can impact bone health.
- Milk allergy or lactose intolerance: These conditions may limit dairy consumption, a significant source of calcium, potentially increasing deficiency risk if alternative calcium food sources are not adequately included in the diet.
For individuals diagnosed with osteoporosis and prescribed calcium supplements, it’s crucial to follow physician guidelines:
- Clarify the total daily calcium intake recommendation, including both dietary and supplemental calcium, typically between 1,000-1,200 mg daily.
- Avoid exceeding 2,000 mg daily, as excessive calcium intake can pose health risks.
- Take calcium supplements in doses of no more than 500 mg at a time to optimize absorption, spacing doses at least 4 hours apart if a higher supplemental dose is prescribed.
- Calcium carbonate supplements are best taken with food for optimal absorption, while calcium citrate can be taken without food.
- Consult a registered dietitian to assess dietary calcium intake and determine the appropriate supplemental amount to meet daily needs, considering calcium food sources already in the diet.
Calcium Toxicity (Hypercalcemia)
Excessive calcium in the blood, known as hypercalcemia, can occur with very high calcium intake. The upper limit for calcium is 2,500 mg daily from food and supplements (2,000 mg for individuals over 50). Exceeding these limits, especially through supplements, can increase the risk of kidney stones, prostate cancer, and constipation. In some individuals, long-term high-dose calcium supplementation might contribute to calcium accumulation in blood vessels and heart problems. Calcium can also interfere with the absorption of other essential minerals like iron and zinc.
Symptoms of hypercalcemia may include:
- Weakness, fatigue
- Nausea, vomiting
- Shortness of breath
- Chest pain
- Heart palpitations, irregular heart rate
Important Considerations
Certain nutrients and medications can increase calcium requirements by reducing calcium absorption or increasing urinary calcium excretion. These include corticosteroids, high sodium intake, phosphoric acid (found in dark cola sodas), excessive alcohol consumption, and oxalates.
Related Resources
Vitamins and Minerals
References
Last reviewed March 2023
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