There was an NIH study of 388,000 people, both men and women. Calcium supplements were caused to increase the risk of cardiovascular death in men. In women, no association was found between calcium supplements and cardiovascular death.
Dietary calcium–calcium from food– was not found to increase this risk.
Take home message: the safest source of calcium is in food. Men should not take calcium supplements.
Want more details? JAMA Internal Med. 2013