An alarming new meta-analysis published in the journal Nutrients titled, "Cardiovascular Effects of Calcium Supplements," brings to the forefront the serious though mainly downplayed health risks associated with calcium supplementation, concluding they increase the risk of heart attack by 27%-31% and the risk of stroke by 12%-20%.
The study based its findings on randomized, placebo-controlled trials, and did not find a lessening of the observed adverse effects with the co-administration of vitamin D. The study noted that the increased cardiovascular risk associated with calcium supplements is consistent with previous epidemiological observations that higher circulating calcium concentrations are linked with cardiovascular disease in normal populations. They postulated that, "There are several possible pathophysiological mechanisms for these effects, including effects on vascular calcification, vascular cells, blood coagulation and calcium-sensing receptors." They concluded that, "[T]he non-skeletal risks of calcium supplements appear to outweigh any skeletal benefits."
The entire study can be viewed on PubMed Central, the free digital database of full-text scientific literature in biomedical and life sciences: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3738985/
In past articles, we delved deeply into the cardiotoxicity of the limestone-, bone meal- or oyster shell-based calcium supplements that dominate the mainstream marketplace, and also the fatally flawed bone mineral density (BMD) guidelines set forth by the World Health Organization in the mid-90's, which essentially reclassified aging as a disease by using the bones of a young adult (25 year old) at peak bone mass as the standard of normality for older women of all ages (i.e. the T-score). As a result of these guidelines, millions of asymptomatic women were suddenly told they had a new 'bone disease' called osteoporosis, and millions more were told they had 'pre-osteoporosis' or 'osteopenia,' an entirely nonsensical disease classification, arbitrarily conceived, and with no basis in biological or physiological fact. [read more: Osteoporosis Myth: The Dangers of High Bone Mineral Density]
This new review only further exemplifies the need for a paradigm shift in the way we understand and contextualize women's health issues. First, we must understand that osteoporosis, in the real-world sense of 'weak' and 'fracture prone' bones, is not caused by a lack of mega-dose calcium derived from limestone. Nor, is it caused by a lack of calcium-rich milk, as the dairy industry has spent quite a lot of time and energy convincing the general public. While one can certainly drive the BMD higher through supplementation, the over-consumption of calcium-rich dairy products, or even worse, chemical 'therapies' such as bisphosphonates, the resulting 'improvements' in BMD may come at the price of decreasing bone quality and the quality and length of the life of the patient as a whole. It is also extremely important to note that research now exists showing that calcium supplementation may actually increase hip fracture risk. 
Furthermore, women in the US and Westernized countries die primarily of heart disease, with cancer a close second, and not complications associated with a bone fracture. [see CDC's top causes of death in females from 2009 below; osteoporosis doesn't even make the top 10]. Insofar as calcium supplementation increases the #1 cause of death in women, their use constitutes a serious, avoidable health risk, removing entirely any justification for their promotion in improving the overall health picture of women.
Considering that nearly 1 in 4 women will die of heart disease, reducing the risk for such an event is extremely important. Therefore, the National Osteoporosis Foundation (NOF) calcium supplementation guidelines (see screenshot below), which suggest women consume between 1,000 mg-1200 mg calcium daily (a range which would require most women take supplemental calcium), place women at significant risk of harm. Considering the NOF name calcium supplement manufacturers such as Bayer-owned Citrical as official corporate partners, it is unlikely they will alter their recommendations anytime soon, even despite the increasingly unequivocal evidence that their guidelines (see below) are doing harm.