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Calcium is a mineral most often associated with healthy bones and teeth, although it also plays an important role in blood clotting, helping muscles to contract, and regulating normal heart rhythms and nerve functions. About 99% of the body’s calcium is stored in bones, and the remaining 1% is found in blood, muscle, and other tissues. In order to perform these vital daily functions, the body works to keep a steady amount of calcium in the blood and tissues. If calcium levels drop too low in the blood, parathyroid hormone (PTH) will signal the bones to release calcium into the bloodstream. This hormone may also activate vitamin D to improve the absorption of calcium in the intestines. At the same time, PTH signals the kidneys to release less calcium in the urine. When the body has enough calcium, a different hormone called calcitonin works to do the opposite: it lowers calcium levels in the blood by stopping the release of calcium from bones and signaling the kidneys to rid more of it in the urine. The body gets the calcium it needs in two ways. One is by eating foods or supplements that contain calcium, and the other is by drawing from calcium in the body. If one does not eat enough calcium-containing foods, the body will remove calcium from bones. Ideally, the calcium that is “borrowed” from the bones will be replaced at a later point. But this doesn’t always happen, and can’t always be accomplished just by eating more calcium. Recommended AmountsThe Recommended Dietary Allowance (RDA) for calcium for women 19-50 years of age is 1,000 mg daily; for women 51+, 1,200 mg. For pregnant and lactating women, the RDA is 1,000 mg. For men 19-70 years of age, the RDA is 1,000 mg; for men 71+ years, 1,200 mg. [1] Calcium and HealthThe reviews below specifically looked at the effect of calcium on various health conditions. Scroll down for links to more information on the health effect of specific foods rich in calcium. Blood pressure Several literature reviews on the topic of total calcium intake, from food and supplements, and blood pressure have suggested a possible link to lowering high blood pressure. However, problems with study designs in these analyses (small numbers of participants, differences among the people studied, and various biases in the types of studies included) prevent a new recommendation for the treatment of high blood pressure that would increase calcium intake above the Recommended Dietary Allowance. [2] Larger trials with longer duration are needed to clarify whether increased calcium intakes or the use of calcium supplements can lower high blood pressure. Cardiovascular disease Some research has raised concerns about calcium supplements and heart health. These studies found that taking calcium supplements increased the risk of cardiovascular events in men and women. It has been suggested that high-dose supplements can cause hypercalcemia (toxic level of calcium in the blood) that can cause blood to clot or the arteries to harden, leading to cardiovascular disease. The connection is not yet clear, but a clinical guideline published after review of the available research from the National Osteoporosis Foundation and the American Society for Preventive Cardiology stated that calcium from food or supplements has no relationship (beneficial or harmful) to cardiovascular disease in generally healthy adults. The guideline advises people not to exceed the Upper Limit for calcium, that is, 2,000-2,500 mg daily from food and supplements. [3] Bone health Calcium is one of the most important nutrients required for bone health. Bone is living tissue that is always in flux. Throughout the lifespan, bones are constantly being broken down and built up in a process known as remodeling. Bone cells called osteoblasts build bone, while other bone cells called osteoclasts break down bone if calcium is needed. In healthy individuals who get enough calcium and physical activity, bone production exceeds bone destruction up to about age 30. After that, destruction typically exceeds production. This is sometimes called “negative calcium balance,” which can lead to bone loss. Women tend to experience greater bone loss than men later in life due to menopause, a condition that lowers the amount of hormones that help to build and preserve bone. Getting enough dietary calcium at all ages may help to slow the degree of bone loss, but calcium intakes at any level are not known to completely prevent bone loss. [4] Calcium is less easily absorbed at later ages, and therefore eating a very high amount of calcium will not always resolve the problem. Studies on calcium intake and bone density in postmenopausal women have mixed results. Possible reasons:
Because the results of some large trials found that higher calcium intakes (usually achieved with a supplement) was associated with improved bone density and slightly lower risk of hip fractures, the RDA for calcium for postmenopausal women is higher than at younger ages. [5] Some studies suggest that frail elderly (80 years and older living in institutions) may benefit from supplementation more than “younger” elderly who live independently in the community. [6] A 2018 review of randomized controlled trials by the U.S. Preventive Services Task Force did not find that supplements with calcium and vitamin D taken for up to 7 years reduced the incidence of fractures in postmenopausal women. These women did not have osteoporosis or a vitamin D deficiency at the start of the study and lived independently in the community. The amount of calcium of the supplements ranged from 600-1,600 mg daily. [7] Colorectal cancer Epidemiological studies following people over time suggest a protective role of high calcium intakes (whether from food and/or supplements) from colorectal cancer. [8] However, randomized controlled trials using calcium supplements, with our without vitamin D, have shown mixed results. One reason may be a fairly short duration. Due to higher cost and difficulty with continued compliance from participants, clinical trials tend to be shorter in duration than epidemiological studies. But colorectal cancer can take 7-10 years or longer to develop, during which these trials might not reflect any changes in the colon.
After a review of both cohort and clinical studies by the World Cancer Research Fund and the American Institute for Cancer Research, they reported strong evidence that calcium supplements of more than 200 mg daily and intake of high-calcium dairy foods will likely decrease the risk of colorectal cancer. [11] They noted possible causes including the ability of calcium to bind to certain toxic substances in the colon and prevent the growth of tumor cells. Certain bacteria in dairy foods may also be protective against the development of cancerous cells in the colon. [12] Kidney stones At one time, experts recommended that people with kidney stones limit their calcium intake because the mineral makes up one of the most common types of stones, called calcium-oxalate stones. What we know now is the reverse—that not eating enough calcium-rich foods can increase the risk of stone formation. Research from large trials including the Women’s Health Initiative and the Nurses’ Health Study found that a high intake of calcium foods decreased the risk for kidney stones in women. However the same effect is not true with supplements, as calcium in pill form was found to increase risk. [13,14] A benefit of calcium-rich foods (mainly from dairy) on the prevention of kidney stones was found in a cohort of 45,619 men. Intakes of skim or low-fat milk and cottage cheese or ricotta cheese showed the greatest protective effect. Men who drank two or more 8-ounce glasses of skim milk a day had 42% less risk of developing kidney stones as compared with men who drank less than one glass a month. Eating two or more half-cup servings of cottage cheese or ricotta cheese a week was associated with 30% less risk of kidney stones as compared with men who ate less than one serving a month. It is believed that calcium-rich foods reduce the formation of stones by lowering the absorption of oxalates, which make up calcium-oxalate stones. However, other undetermined components of dairy foods may also be responsible for the decreased risk. [15] Food SourcesCalcium is widely available* in many foods, not just milk and other dairy foods. Fruits, leafy greens, beans, nuts, and some starchy vegetables are good sources.
Signs of Deficiency and ToxicityDeficiencyBlood levels of calcium are tightly regulated. Bones will release calcium into the blood if the diet does not provide enough, and no symptoms usually occur. A more serious deficiency of calcium, called hypocalcemia, results from diseases such as kidney failure, surgeries of the digestive tract like gastric bypass, or medications like diuretics that interfere with absorption. Symptoms of hypocalcemia:
A gradual, progressive calcium deficiency can occur in people who do not get enough dietary calcium in the long-term or who lose the ability to absorb calcium. The first early stage of bone loss is called osteopenia and, if untreated, osteoporosis follows. Examples of people at risk include:
Guidelines if you are taking calcium supplements for osteoporosis After a diagnosis of osteoporosis, your physician may prescribe over-the-counter calcium supplements. However, there are several points to consider when using calcium supplements.
ToxicityToo much calcium in the blood is called hypercalcemia. The Upper Limit (UL) for calcium is 2,500 mg daily from food and supplements. People over the age of 50 should not take more than 2,000 mg daily, especially from supplements, as this can increase risk of some conditions like kidney stones, prostate cancer, and constipation. Some research has shown that in certain people, calcium can accumulate in blood vessels with long-term high doses and cause heart problems. Calcium is also a large mineral that can block the absorption of other minerals like iron and zinc. Symptoms of hypercalcemia:
Did You Know?Certain nutrients and medications may increase your need for calcium because they either lower the absorption of calcium in the gut or cause more calcium to be excreted in the urine. These include: corticosteroids (example: prednisone), excess sodium in the diet, phosphoric acid such as found in dark cola sodas, excess alcohol, and oxalates (see Are anti-nutrients harmful?). References
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