Long-Term Calcium Supplement Side Effects

Common Side Effects

Gastrointestinal symptoms are the most frequent adverse effects, including constipation, dyspepsia, bloating, and abdominal cramping 2
Increased risk of kidney stones (nephrolithiasis) with calcium supplementation, with a relative risk of 1.17 in the Women's Health Initiative trial 2, 4
The risk of kidney stones appears to be dose-dependent 2

Evidence regarding cardiovascular risks is inconsistent and controversial 2, 5
Some meta-analyses have suggested an increased risk of myocardial infarction with calcium supplementation (odds ratio 1.27; 95% CI, 1.01 to 1.59) 4, 6
Proposed mechanism involves transient increases in serum calcium levels potentially precipitating arrhythmias or promoting vascular calcification 4
However, the Women's Health Initiative trial involving over 36,000 women showed no significant increase in cardiovascular events or mortality 2, 5
A Swedish cohort study found increased cardiovascular and all-cause mortality in women with calcium intake ≥1400 mg/day, but not with intakes of 1000-1399 mg/day 5

The Institute of Medicine recommends daily calcium intake of 1000 mg for women 19-50 years and men 19-70 years, and 1200 mg for women over 50 and men over 70 years 3
Upper intake levels should not exceed 2500 mg/day for adults under 50 and 2000 mg/day for those over 50 3
Dietary sources of calcium are preferred over supplements whenever possible 5, 3
If supplements are necessary, they should be taken in divided doses not exceeding 500 mg of elemental calcium at one time 3

The American College of Cardiology guidelines are not mentioned, however, the New England Journal of Medicine suggests a reasonable approach is to preferentially encourage dietary calcium intake and discourage routine use of calcium supplements 5
For those unable to meet calcium requirements through diet alone, supplements should be used judiciously to reach but not exceed recommended daily intake levels 3