Abnormally elevated blood calcium ('hypercalcemia') has been reported only with the consumption of large quantities of calcium supplements (1.5 to 16.5 g/day), usually in combination with calcium carbonate ('antacids') and milk to treat open, painful wounds in the stomach ('peptic ulcers') (1). Mild hypercalcemia may be without symptoms or may result in loss of appetite, nausea, and vomiting, while more severe hypercalcemia may result in confusion, delirium, coma, and if not treated, death. Since the treatment for peptic ulcers has changed, the incidence of this syndrome has decreased considerably (2).
Although the risk of forming kidney stones is increased in individuals with abnormally elevated urinary calcium, this condition is not usually related to calcium intake, but rather to increased excretion of calcium by the kidneys (53).
Calcium and prostate cancer risk
Epidemiological studies have raised concern that high calcium intakes are associated with increased risk of prostate cancer:
A large prospective cohort study in the U.S. followed more than 50,000 male health professionals for eight years and found that men whose calcium intake was 2,000 mg/day or more had a risk of developing advanced prostate cancer that was three times higher than men whose calcium intake was less than 500 mg/day and a risk of developing spreading ('metastasized') prostate cancer that was more than four times greater (54). Similar results were observed in a case-control study in Sweden (55).
Neither study found calcium intake to be associated with an increased risk of total prostate cancer or non-advanced prostate cancer.
More recently, a prospective study in a group of 29,133 male smokers, followed for 17 years, found that high calcium consumption (more than 1,000 mg/day) was associated with an increased risk of prostate cancer (56).
The physiologic mechanisms underlying the relationship between calcium intake and prostate cancer are not yet clear. High levels of dietary calcium may lead to decreased circulating levels of vitamin D (calcitriol), which showed prostate cancer-protective effects in animals. However, the findings of studies conducted in humans on blood calcitriol levels and prostate cancer risk have been much less consistent.
Not all epidemiological studies have demonstrated an association between calcium intake and prostate cancer: one review reported that (only) seven out of 14 case-control studies and five out of nine prospective cohort studies found statistically significant positive associations between prostate cancer and some measure of dairy product consumption (e.g., calcium intake) (57). A meta-analysis of six prospective studies reported that men with higher daily calcium intakes had a 39% increased risk of developing prostate cancer compared to those with lower intakes (58). However, only half of the distinct studies included in this meta-analysis reported an association between higher calcium intakes and prostate cancer.
More recently, a prospective study in 14,642 men participating in the Melbourne Collaborative Cohort Study found that calcium intake was not associated with prostate cancer risk (59). Repeating the meta-analysis (58) to include this study (59), it was found that dairy intake was no longer associated with a significantly increased risk of prostate cancer (59).
The inconsistent study results suggest complex interactions among the risk factors for prostate cancer and may also reflect the difficulties associated with assessing calcium intake in humans.
Until the relationship between calcium and prostate cancer is clarified, it is reasonable for men to consume the recommended adequate intake level of a total of 1,000 to 1,200 mg/day calcium (2).
Tolerable upper intake level
The European Food Safety Authority has established a tolerable upper intake level (UL) for calcium intake only for adults: 2,500 mg/day (43). This UL applies also to pregnant and breast-feeding women. Scientific data have been considered insufficient to derive an UL for children and adolescents.
In 2010, the U.S. Institute of Medicine has set a tolerable upper level (UL) of intake for calcium (61):
Age Group | UL (mg/day) |
| Infants 0–6 months | 1,000 |
| Infants 6–12 months | 1,500 |
| Children 1–8 years | 2,500 |
| Children 9–13 years | 3,000 |
| Adolescents 14–18 years | 3,000 |
| Adults 19 – 50 years | 2,500 |
| Adults 51 and older | 2,000 |
| 14 – 18 years old pregnant/lactating women | 3,000 |
| 19 – 50 years old pregnant/lactating women | 2,500 |
Drug interactions
Please note:
Because of the potential for interactions, dietary supplements should not be taken with medication without first talking to an experienced healthcare provider.
Calcium-mineral interactions
The presence of calcium decreases iron absorption from most supplements and food sources other than meat. However, calcium supplementation up to 12 weeks has not been found to change iron nutritional status, probably due to a compensatory increase in iron absorption. Individuals taking iron supplements should take them two hours apart from calcium-rich foods or supplements to maximize iron absorption.
High calcium intakes have produced relative magnesium deficiencies in animals, but calcium intake was not found to affect magnesium retention in humans (1).
Although a number of studies did not find high calcium intakes to affect zinc absorption or zinc nutritional status, a study in ten men and women indicated that 600 mg of calcium consumed with a meal decreased the absorption of zinc from that meal by 50% (60).