Calcium is an essential mineral responsible for many physiological functions in the body. It is stored in the bones and helps maintain bone structure. Calcium also plays an important role in cell signaling and muscle contraction. Dietary calcium can be found in dairy products, nuts and fish. Pregnant and breast-feeding women, children, the elderly, and post-menopausal women may require higher intake (1) (2) (3). Natural supplements are derived from minerals, oyster shells and occasionally corals.
Calcium has been studied for its use in treating a range of conditions, including osteoporosis, bone density loss (4) (5), premenstrual syndrome (PMS) (6) (7), preeclampsia (8), lead poisoning (9), and colon (10) and prostate cancer. Calcium supplementation may have beneficial effects on cardiovascular risk factors such as hypertension (11) (12) (13) but this effect has not been shown in postmenopausal women (14). Because low dietary intake of calcium may reduce bone mass and increase the risk of osteoporosis, several studies have addressed the effects of calcium with or without vitamin D supplementation on bone mineral density (15) (16).
Studies of calcium supplementation with or without vitamin D3 and fracture prevention in the elderly offer conflicting data (17) (18).
In postmenopausal women, neither hip fracture (19) nor physical decline (20) was reduced. But some studies found benefits in adults in over age 50 and in premenopausal women (21) (22). However, according to the latest statement from the U.S. Preventive Services Task Force (USPSTF), current evidence is insufficient to assess the balance of the benefits and harms of combined vitamin D and calcium supplementation for the primary prevention of fractures in premenopausal women or in men. Evidence is also lacking to determine the balance of the benefits and harms of daily supplementation with greater than 400 IU of vitamin D3 and greater than 1000 mg of calcium for the primary prevention of fractures in noninstitutionalized postmenopausal women. The USPSTF recommends against daily supplementation with 400 IU or less of vitamin D3 and 1000 mg or less of calcium for the primary prevention of fractures in noninstitutionalized postmenopausal women (35).
Data also suggest that increasing dietary intake of calcium does not benefit cardiovascular health (34), while the supplemental form may increase the risk of cardiovascular events (31) and myocardial infarction(34).
Calcium is thought to have a protective effect against cancer. However, the Women's Health Initiative study found no association between calcium and vitamin D supplementation and reduced risk of colorectal cancer (24) or invasive cancer and mortality (33) in postmenopausal women. Subsequent reanalysis suggested that estrogen therapy may interact with the supplements (25). Data from a randomized trial indicate a significant reduction in risk of cancer in postmenopausal women following vitamin D and calcium supplementation (26). In men, calcium intake may reduce risk of colorectal cancer (26), but may increase the risk of prostate cancer (27).
Studies also showed that supplemental calcium blocks absorption of lead from other foods (23). In children with lead poisoning, calcium supplementation had no effect on blood lead levels (9). Calcium supplements may cause constipation and gastrointestinal upset. Some calcium salts can neutralize gastric acid and can interfere with absorption of prescription medications, (28); Caffeine may lower calcium absorption and increase urinary calcium excretion (29). A few cases of kidney stones have been reported at high doses.
A recent report from the Institute of Medicine recommends a Dietary Allowance at 1,000mg/day for bone health. Adolescents and pregnant/lactating women may need up to 1,300 mg/day (32). Patients should consult with their physicians if more calcium is needed for health maintenance.