Osteoporosis is not caused by a lack of limestone, oyster shell or bone meal. Heart attack, however, may be caused by supplementation with these exact same "elemental" forms of calcium, according to two meta-analyses published last year in the British Medical Journal.
Back in July of 2011, the British Medical Journal published the results of a high-powered meta-analysis which looked at whether or not calcium supplementation had any effect on cardiovascular disease risk. Indeed, this groundbreaking report, which was based on the results of five clinical trials conducted in the US, Britain and New Zealand, involving over 8,000 people, showed that taking elemental calcium supplements of 500 mg or more increased the relative risk of heart attack by 27%.
Though the study made international headlines at the time, critics soon took issue with the fact that it involved calcium supplementation without co-administered vitamin D. However, in April of that same year, another meta-analysis published in the same journal showed that even with co-administered D elemental calcium increased the risk of heart attack by 24%, and in addition, the composite of heart attack and stroke by 15% -- in essence, putting those doubts to rest.
The idea that calcium supplementation may be toxic to cardiovascular health is not new, as many in the field of nutrition have long warned against supplementation with elemental calcium; which is to say, calcium from limestone, oyster shell, egg shell and bone meal (hydroxylapatite).
Despite the growing popularity of elemental calcium supplementation, largely reinforced by conventional health "experts" and organizations like the National Osteoporosis Foundation (whose corporate sponsors include the calcium manufacturers Oscal and Citrical), the habit simply does not make sense. After all, have you ever experienced visceral disgust after accidentally consuming eggshell? If you have, you know your body is "hard-wired" to reject low-quality calcium sources (stones and bones as it were), in favor of getting calcium from food.
Inorganic or "elemental" calcium, when not bound to the natural co-factors, e.g. amino acids, lipids and glyconutrients, found in "food" (which is to say other living beings, e.g. plants and animals), no longer has the intelligent delivery system that enables your body to utilize it in a biologically appropriate manner. Lacking this "delivery system," the calcium may end up going to places you do not want (ectopic calcification), or go to places you do want (e.g. the bones), but in excessive amounts, stimulating unnaturally accelerated cell-division (osteoblasts), resulting in higher bone turn over rates later in life (this is explained in the article below).