Many people take calcium supplements to protect bone density, yet, taken by itself is apparently not without risk.
Researchers from the University of Auckland and University of Aberdeen demonstrated that calcium supplements, without co-administered vitamin D, is associated with an increased risk of heart attack (Bolland, Avenell, Baron, Grey, MacLennan, Gamble, Reid, 2010). This meta-analysis reviewed 15 studies with a total of 20,172 participants, aged 40 years and over, consuming a total of 500 mg of calcium per day. The average duration of each study critiqued was approximately four years.
It was found that subjects using calcium supplements had a 27 to 31 percent higher risk of heart attack than individuals who did not use a calcium supplement. Moreover, an increase in the risk of stroke and overall mortality was indicated, however, was not considered statistically significant. It was reported that an increased risk of heart attack was consistent and unrelated to gender, age, or brand/form of calcium supplement. It was also noted that calcium supplements were largely ineffective in reducing the risk of bone fractures.
Bolland, M.J., Avenell, A., Baron, J.A., Grey, A, MacLennan, G.S., Gamble, G.D. & Reid, I.R. 2010. Effect of calcium supplements on risk of myocardial infarction and cardiovascular events: meta-analysis. British Journal of Medicine, 341:c3691. doi: 10.1136/bmj.c3691.