What does calcium do?
Although calcium plays at least some minor role in lowering blood pressure, the mechanisms involved appear complex and somewhat unclear.1 The level of calcium in the blood is tightly regulated by parathyroid hormone (PTH), and low intake of calcium causes elevations in PTH, which in turn have been implicated in the development of hypertension.2 High calcium intake has also been associated with a reduced risk of cardiovascular disease in postmenopausal women.3
By reducing absorption of oxalate,4 a substance found in many foods, calcium may be able to indirectly reduce the risk of kidney stones.5 However, people with a history of kidney stones must talk with a doctor before supplementing with calcium because such supplementation might actually increase the risk of forming stones for the small number of people who absorb too much calcium.
Calcium also appears to partially bind some fats and cholesterol in the gastrointestinal tract. Perhaps as a result, some research suggests that calcium supplementation may help lower cholesterol levels.6
Animal studies have established a role of calcium in the development of female egg cells (oocytes).7 8 Although the precise role of calcium is unclear, some researchers speculate that future studies may identify important uses for calcium in conditions of the human ovary, such as polycystic ovary syndrome (PCOS).9
Through a variety of mechanisms, calcium may have anticancer actions within the colon. Most preliminary studies have shown high calcium diets are associated with reduced colon cancer risk.10 Most,11 12 13 but not all,14 preliminary studies have found taking calcium supplements to also be associated with a reduced risk of colon cancer or precancerous conditions in the colon. One preliminary study reported that high dietary, but not supplemental, calcium intake was associated with a decreased risk of precancerous changes in the colon.15 In double-blind studies, calcium supplementation has significantly protected against precancerous changes in the colon in some,16 17 but not all, studies.18 19
Warning: Calcium supplements should be avoided by prostate cancer patients.
Where is calcium found?
Calcium has been used in connection with the following conditions
Who is likely to be deficient of calcium?
How much calcium is usually taken?
Are there any side effects or interactions with calcium?
People with hyperparathyroidism, chronic kidney disease, or kidney stones should not supplement with calcium without consulting a physician. For other adults, the highest amount typically suggested by doctors (1,200 mg per day) is considered quite safe. People with prostate cancer should avoid supplementing with calcium.
In the past, calcium supplements in the forms of bone meal (including MCHC), dolomite, and oyster shell have sometimes had higher lead levels than permitted by stringent California regulations, though generally less than the levels set by the federal government.25 “Refined” forms (which would include CCM, calcium citrate, and most calcium carbonate) have low levels.26 More recently, a survey of over-the-counter calcium supplements found low or undetectable levels of lead in most products,27 representing a sharp decline in lead content of calcium supplements since 1993. People who decide to take bone meal, dolomite, oyster shell, or coral calcium for long periods of time can contact the supplying supplement company to request independent laboratory analysis showing minimal lead levels.
Calcium competes for absorption with a number of other minerals. Therefore, people taking calcium for more than a few weeks should also take a multimineral supplement.
One study has shown that taking calcium can interfere with the absorption of phosphorus, which, like calcium, is important for bone health.28 . Although most western diets contain ample or even excessive amounts of phosphorus, older people who supplement with large amounts of calcium may be at risk of developing phosphorus deficiency. For this reason, the authors of this study recommend that, for elderly people, at least some of the supplemental calcium be taken in the form of tricalcium phosphate or some other phosphorus-containing preparation.
Vitamin D’s most important role is maintaining blood levels of calcium. Therefore, many doctors recommend that those supplementing with calcium also supplement with 400 IU of vitamin D per day.
Animal studies have shown that essential fatty acids (EFAs) increase calcium absorption from the gut, in part by enhancing the effects of vitamin D and reducing loss of calcium in the urine.29
Lysine supplementation increases the absorption of calcium and may reduce its excretion.30 As a result, some researchers believe that lysine may eventually be shown to have a role in the prevention and treatment of osteoporosis.31
Are there any drug interactions?