A meta-analysis (high level of evidence) of trials of calcium supplements found a 27%–31% increase in risk of myocardial infarction (heart attack), and a 12%–20% increase in risk of stroke. These findings are based on randomized, placebo-controlled trials and are consistent across the trials. Taken together with vitamin D does not lessen these adverse effects.
The analysis also found no benefit in osteoporosis prevention.
However, food and whole herbs are consistently found to be protective, together with lifestyle changes such as resistance exercise and stress management.
This should dispel the myth that we need to take any synthetic calcium supplement and high calcium food such as cow’s milk.
Reid, I.R. (2013) Cardiovascular Effects of Calcium Supplements. Nutrients,5, 2522-2529,doi:10.3390/nu5072522