top view wooden board with various cheese, nuts, broccoli, canned fish, and jug of milk
Calcium is a vital mineral, renowned for its crucial role in maintaining strong and healthy bones and teeth. However, its importance extends far beyond skeletal health. Calcium plays an integral part in numerous bodily functions, including blood clotting, muscle contractions, regulating heart rhythms, and nerve signal transmission. With 99% of the body’s calcium diligently stored in bones, the remaining 1% circulates in the blood, muscles, and other tissues, underscoring its dynamic role throughout the body. Ensuring you consume enough calcium-rich foods is paramount for overall well-being.
Understanding Calcium and Its Role in Your Body
To sustain these essential daily functions, your body diligently works to maintain a consistent level of calcium in your bloodstream and tissues. When blood calcium levels dip too low, the parathyroid hormone (PTH) acts as a messenger, signaling bones to release calcium into the bloodstream. This intricate hormonal dance also involves vitamin D activation, which enhances calcium absorption in the intestines. Simultaneously, PTH prompts the kidneys to reduce calcium excretion in urine, conserving this precious mineral. Conversely, when calcium levels are sufficient, calcitonin, another hormone, steps in to lower blood calcium levels. It achieves this by inhibiting calcium release from bones and instructing the kidneys to eliminate more calcium through urine.
Your body secures the calcium it needs through two primary avenues: consuming calcium-containing foods or supplements and drawing upon the calcium reserves stored within the body, primarily in bones. If your dietary intake of calcium-rich foods is insufficient, your body will inevitably tap into bone calcium. Ideally, this “borrowed” calcium is replenished later. However, this isn’t always guaranteed, and simply increasing calcium intake afterward may not fully rectify the deficit. Therefore, consistently consuming foods rich in calcium is crucial for maintaining optimal calcium balance and overall health.
Recommended Daily Calcium Intake
The amount of calcium you need daily varies depending on age and sex. Health organizations provide Recommended Dietary Allowances (RDAs) to guide your intake. For women aged 19-50 years, the RDA for calcium is 1,000 mg daily, increasing to 1,200 mg for women aged 51 and older. Pregnant and lactating women require 1,000 mg of calcium daily. Men aged 19-70 years are recommended to consume 1,000 mg of calcium per day, while men aged 71 and older should aim for 1,200 mg daily. Meeting these recommended amounts through calcium-rich foods is essential for supporting bone health and overall bodily functions.
Health Benefits of Calcium
Calcium’s impact on health is wide-ranging, extending from bone integrity to cardiovascular and even cancer risk. Let’s delve into some key health benefits associated with adequate calcium intake.
Bone Health
Calcium is undeniably a cornerstone nutrient for bone health throughout life. Bone is dynamic tissue, constantly undergoing a remodeling 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 youth and with sufficient calcium and physical activity, bone formation outpaces bone breakdown, typically until around age 30. After this point, bone breakdown gradually exceeds formation, potentially leading to bone loss, sometimes termed “negative calcium balance.” This can increase the risk of osteoporosis, a condition characterized by weakened bones. Women are particularly susceptible to bone loss later in life due to menopause, which reduces estrogen levels, a hormone that supports bone building and preservation.
Consuming enough dietary calcium throughout life can help slow down bone loss, although it may not completely prevent it. Calcium absorption also becomes less efficient with age, meaning very high calcium intakes might not fully compensate for age-related absorption decline. Studies investigating calcium intake and bone density in postmenopausal women have yielded mixed results. Some studies focused solely on calcium supplements, neglecting dietary calcium intake, while others didn’t account for hormone replacement therapy or vitamin D supplementation, factors that influence bone health.
Despite some mixed findings, research suggests that higher calcium intakes, often achieved through supplementation, can improve bone density and slightly reduce hip fracture risk, particularly in postmenopausal women. This is why the RDA for calcium is higher for this group. However, a 2018 review of randomized controlled trials found that calcium and vitamin D supplements for up to 7 years did not reduce fracture incidence in postmenopausal women without osteoporosis or vitamin D deficiency. Therefore, focusing on consistent calcium intake from food sources alongside other bone-healthy habits remains crucial.
Cardiovascular Health
The relationship between calcium and cardiovascular health is complex and has been a subject of ongoing research and some debate. Some studies have raised concerns about calcium supplements and heart health, suggesting a potential link between high-dose supplements and increased cardiovascular event risk. It’s been proposed that excessive calcium from supplements could lead to hypercalcemia (toxic blood calcium levels), potentially causing blood clots or artery hardening, contributing to cardiovascular disease. However, the evidence is not yet conclusive, and 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 has no clear beneficial or harmful relationship with cardiovascular disease in generally healthy adults. The guideline advises against exceeding the Upper Limit for calcium (2,000-2,500 mg daily from food and supplements).
It’s important to note that the potential concerns are primarily associated with high-dose calcium supplements, not calcium obtained from food sources. Prioritizing calcium-rich foods as part of a balanced diet is generally considered safe and beneficial for overall health, including cardiovascular well-being.
Blood Pressure
Several literature reviews have explored the connection between total calcium intake (from both food and supplements) and blood pressure, suggesting a possible link to lowering high blood pressure. However, limitations in study designs, such as small participant numbers, variations among study populations, and biases in included studies, prevent definitive recommendations to increase calcium intake above the RDA specifically for high blood pressure treatment. Larger, longer-term trials are needed to clarify whether increased calcium intake or calcium supplementation can effectively lower high blood pressure. While the evidence is not conclusive enough to recommend increased calcium intake solely for blood pressure management, maintaining adequate calcium levels through diet remains important for overall health, which indirectly supports healthy blood pressure.
Colorectal Cancer
Epidemiological studies that follow populations over time suggest a potential protective role of high calcium intake (from food and/or supplements) against colorectal cancer. However, randomized controlled trials using calcium supplements, with or without vitamin D, have shown mixed results, possibly due to relatively short trial durations compared to the long development time of colorectal cancer (7-10 years or more).
Despite some mixed trial outcomes, a Cochrane review of well-designed studies found that 1,200 mg of daily elemental calcium for about 4 years reduced new colorectal adenoma incidence by 26%. Adenomas are non-cancerous tumors that can become cancerous. Conversely, a large trial from the Women’s Health Initiative found no colorectal cancer incidence difference between women taking calcium and vitamin D supplements and those taking a placebo over about 7 years, with a follow-up study also showing no difference after 11 years. However, these studies noted that participants already had high calcium intake at baseline, potentially diminishing the impact of supplementation.
The World Cancer Research Fund and the American Institute for Cancer Research, after reviewing both cohort and clinical studies, reported strong evidence that calcium supplements exceeding 200 mg daily and high-calcium dairy intake likely decrease colorectal cancer risk. Possible mechanisms include calcium binding to toxic substances in the colon and inhibiting tumor cell growth. Certain bacteria in dairy foods may also offer protection against cancerous colon cell development. While research is ongoing, incorporating calcium-rich foods, particularly dairy, into your diet may contribute to colorectal cancer risk reduction.
Kidney Stones
Contrary to earlier beliefs, experts now understand that restricting calcium intake is not advisable for preventing kidney stones. In fact, inadequate calcium-rich food consumption can increase kidney stone formation risk. Research from large trials like the Women’s Health Initiative and the Nurses’ Health Study demonstrated that higher calcium food intake decreased kidney stone risk in women. However, calcium supplements, in pill form, were found to increase risk.
A study in men also found that calcium-rich foods, especially dairy, were protective against kidney stones. Skim or low-fat milk and cottage or ricotta cheese showed the strongest protective effects. 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 monthly. Similarly, consuming two or more half-cup servings of cottage or ricotta cheese weekly was linked to a 30% reduced risk compared to less frequent consumption. It’s believed that calcium-rich foods reduce stone formation by decreasing oxalate absorption, a key component of calcium-oxalate stones. Other components in dairy foods might also contribute to this protective effect. Therefore, including calcium-rich foods in your diet is recommended, even for individuals prone to kidney stones, while calcium supplements should be used cautiously.
Top Food Sources of Calcium
Calcium is readily available in a diverse array of foods, extending beyond milk and dairy products. Fruits, leafy greens, beans, nuts, and certain starchy vegetables are all valuable sources.
Dairy Products
Dairy products like milk, cheese, and yogurt are often highlighted as excellent calcium sources. They generally contain significant amounts of calcium and are readily absorbed by the body. For instance, one cup of milk provides approximately 300mg of calcium. Cheese and yogurt are also calcium-dense, with variations depending on the type and serving size. Choosing low-fat or fat-free dairy options can help manage calorie intake while still reaping calcium benefits.
Leafy Green Vegetables
Certain leafy green vegetables offer a surprising amount of calcium. Bok choy, kale, collard greens, and turnip greens are good examples. While the total calcium content might be lower than in dairy on a per-serving basis, the calcium in some leafy greens boasts higher bioavailability, meaning a larger percentage is absorbed by the body. For example, cooked bok choy has around 160mg of calcium per cup, with about 50% bioavailability, meaning roughly 80mg is absorbed. This makes it a comparable calcium source to milk in terms of absorbable calcium. It’s important to note that spinach, while high in total calcium, also contains oxalates, which significantly reduce calcium bioavailability, making it a less efficient calcium source compared to other leafy greens.
Nuts and Seeds
Nuts and seeds contribute to calcium intake, although in smaller amounts compared to dairy or some leafy greens. Almonds, sesame seeds, chia seeds, and flax seeds contain calcium, along with other beneficial nutrients like healthy fats and fiber. Adding these to your diet can contribute to your overall calcium intake, especially for those who limit dairy consumption.
Beans and Legumes
Beans and legumes, such as white beans, kidney beans, soybeans, and tofu (especially calcium-set tofu), provide calcium and are excellent plant-based protein sources. Calcium-set tofu is particularly noteworthy as its calcium content and bioavailability can be similar to milk. Incorporating beans and legumes into meals is a nutritious way to boost calcium intake, particularly for vegetarians and vegans.
Fortified Foods
Fortified foods are enriched with added calcium, offering convenient ways to increase calcium intake. Calcium-fortified orange juice, plant-based milk alternatives (almond milk, soy milk, oat milk), and breakfast cereals are common examples. These fortified options can be particularly helpful for individuals who avoid dairy or have difficulty meeting calcium needs through whole foods alone. Always check product labels to confirm calcium fortification levels.
Understanding Calcium Bioavailability
Calcium bioavailability refers to the proportion of calcium in food that your body actually absorbs and utilizes. Not all calcium consumed is equally absorbed. Calcium is a relatively large mineral and not easily broken down in the gut. The calcium amount listed on food labels reflects the total calcium content, not necessarily the amount your body will absorb.
Dairy products have a calcium bioavailability of around 30%. So, if milk lists 300mg of calcium per cup, approximately 100mg will be absorbed and used. Plant foods like some leafy greens may contain less total calcium but exhibit higher bioavailability than dairy. Calcium-fortified orange juice and calcium-set tofu have bioavailability similar to milk. Almonds have slightly lower total calcium and about 20% bioavailability.
“Anti-nutrients” naturally present in some plant foods, such as oxalates and phytates, can bind to calcium and reduce its bioavailability. Spinach, despite its high total calcium content, is also high in oxalates, resulting in low bioavailability (around 5%). While spinach remains nutritious, it shouldn’t be relied upon as a primary calcium source.
To optimize calcium absorption, consider meal timing. Avoid consuming “calcium-binding” foods like spinach simultaneously with calcium-rich foods or calcium supplements. Aim to meet the RDAs for calcium, considering that these recommendations account for typical calcium bioavailability in food. Individual calcium absorption can vary based on metabolism and other foods consumed in the same meal. Eating a variety of calcium-rich foods helps offset potential absorption variations.
Calcium Deficiency and Toxicity
Maintaining calcium balance is crucial. Both calcium deficiency and excess can lead to health issues.
Calcium Deficiency (Hypocalcemia)
Blood calcium levels are tightly regulated. If dietary calcium is insufficient, bones will release calcium into the blood, often without immediate symptoms. However, severe calcium deficiency, known as hypocalcemia, can result from underlying conditions like kidney failure, digestive tract surgeries (e.g., gastric bypass), or medications like diuretics that interfere with absorption.
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, stemming from inadequate dietary intake or impaired absorption, can lead to osteopenia (early bone loss) and eventually osteoporosis if unaddressed. Groups at higher risk 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: Disrupted or ceased menstrual periods, often seen in young women with anorexia nervosa or athletes with extreme training regimens.
- Milk allergy or lactose intolerance: Impaired digestion of lactose (milk sugar) or milk proteins (casein, whey). Lactose intolerance can be genetic or acquired due to prolonged lactose avoidance.
For individuals diagnosed with osteoporosis and taking calcium supplements, certain guidelines are important:
- Consult your physician to determine your total daily calcium needs (including food and supplements). Exceeding 2,000 mg daily is generally not recommended, even for osteoporosis.
- Take calcium supplements in divided doses of no more than 500 mg at a time, as larger doses at once can reduce absorption. Space doses at least 4 hours apart if taking more than 500 mg daily.
- Calcium carbonate supplements are best taken with food for optimal absorption, as they require stomach acid for breakdown. Calcium citrate can be taken without food.
- Consult a registered dietitian if unsure about dietary calcium intake to determine the appropriate supplement dosage to complement your diet.
Calcium Toxicity (Hypercalcemia)
Excessive calcium in the blood is termed hypercalcemia. The Upper Limit (UL) for calcium is 2,500 mg daily from food and supplements, with a lower UL of 2,000 mg for individuals over 50, especially from supplements, due to potential increased risks of kidney stones, prostate cancer, constipation, and cardiovascular issues in susceptible individuals with long-term high doses. Excess calcium can also 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 absorption or increasing excretion. These include corticosteroids (e.g., prednisone), excess sodium intake, phosphoric acid (found in dark cola sodas), excessive alcohol consumption, and oxalates.
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References
Last reviewed March 2023
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