Every day, our bodies create new bone. In a process known as remodeling, new bone tissue is laid down and old tissue is reabsorbed. In individuals with healthy bones, a state of homeostasis or balance is achieved between these two activities.
Calcium is an essential component in the creation of new bone and in maintaining bone health. During the remodeling process, thousands of milligrams of calcium move in and out of the bone matrix (or scaffold) and are filtered by the kidney. Much of this calcium is reabsorbed and reused by the body, but a certain amount is excreted primarily by the kidneys, and the gastrointestinal system.
To compensate for this loss, itís important to replenish calcium, preferably through diet, but if necessary, through calcium supplements. Prolonged deficiency of calcium can lead to osteoporosis, a condition in which the bones are weakened and are at increased risk of fracture.
Numerous agencies and organizations concerned with bone health have offered guidelines and recommendations for daily calcium intake. Although these recommendations are generally in agreement with one another, research on the efficacy of calcium in preventing fractures and estimates of how wide spread calcium deficiency is in the general population, have yielded some conflicting results.
In addition, published recommendations are usually directed at normal, healthy individuals and may not apply to those with specific medical conditions such as kidney impairment.
For example, in 1997, the US National Academy of Sciences (NAS) set guidelines of 1200 mg of elemental calcium as the recommended daily intake for adults over the age of 50 [1-4]. Nutritional surveys based on data collected between 2003-2006 (such as the National Health and Nutrition Evaluation Surveys, NHANES) reported that fewer than 10% of women up to the age of 70 and fewer than 1% after 70 years, along with fewer than 25% of adult men met the NAS guidelines for dietary calcium.
When the Bailey et al update of the 2003-2006 NHANES database was used to estimate calcium intakes from food, water, dietary supplements, and antacids for U.S. citizens, researchers found:
In contrast to earlier findings, in which a significant proportion of the adult population had very low calcium intakes, the 2010 Bailey et al update of the NHANES report showed that a much greater percentage of people are meeting, and some, in fact, exceeding daily recommended intakes. 
The increase in calcium intake is attributed to a greater consumption of supplemental calcium; about 43% of the U.S. population and almost 70% of older females reported supplemental calcium use. Given these findings, it is important to consider both the benefits and any potential risks of supplementation.
Read more about the facts and recommendations for calcium intake by referring to the links at the end of this article under Additional Reading.
Individuals with impaired renal (kidney) function, older persons, and those with gastrointestinal disorders with malabsorption, should consult with their physicians about the level of calcium that is appropriate for them.
Itís also important to consider the source of calcium consumed. While some authorities claim that calcium obtained from dietary sources offers greater benefit than that obtained from supplements, few studies have compared dietary to supplemental calcium in a meaningful way.
For example, one study compared bone mineral density (BMD) changes at the trochanter (a specific region of the upper end of the femur or thigh bone) in 168 subjects receiving placebo, milk powder or a standard calcium carbonate supplement over a two-year period. 
Results showed that the powder and the supplement were equally effective in preventing bone loss.
Evidence that calcium supplementation reduces an individualís risk of fracture would in fact be the most convincing proof of skeletal benefit. The effect on fracture risk reduction with the use of calcium alone in small, randomized trials have not consistently shown a statistically significant effect. Multiple meta-analyses (analysis of the combined results of a number of studies) have been conducted to evaluate the magnitude of the effect.
Evidence from trials with 52,625 subjects showed a 12% risk reduction of fracture. In a subgroup analysis, the fracture risk reduction was even greater (a 24% reduction) when compliance was high (greater than 80%) and when calcium supplementation was equal to or greater than 1200 mg per day. The addition of Vitamin D did not detract from the calcium-associated benefits in fracture risk reduction. 
A recent report commissioned by the US Preventative Task Force (USPTF), published in November 2011, based on a meta-analysis of 16 clinical trials. This report purports to show no proven benefit in terms of fracture risk reduction for calcium and Vitamin D supplementation. his report is contradicted by the 1000 page, 6-year comprehensive survey from the Institute of Medicine in 2010. 
Despite conflicting conclusions from two government sponsored studies, the weight of evidence and experience supports the belief that the current levels of calcium and Vitamin D, as recommended in the Institute of Medicineís report, are safe and beneficial for bone health. These recommendations are:
The following websites are provided to inform about the general facts and recommendations for dietary intake.
1. Standing Committee on the Scientific Evaluation of Dietary Reference Intakes FaNBIoM 1997 Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D and Fluoride. National Academy Press, Washington, DC, USA
2. U.S. Department of Agriculture (1993a) Continuing Survey of Food Intakes by Individuals (CSFn): diet and health knowledge survey 1989. U.S. Department of Commerce, National Technical Information Service, Springfield, VA (PB93500411: machine readable data set).
3. U.S. Department of Agriculture (1993b) Continuing Survey of Food Intakes by Individuals (CSFn): diet and health knowledge survey 1990. U.S. Department of Commerce, National Technical Information Service, Springfield, VA (PB93504843: machine read able data set).
4. U.S. Department of Agriculture (1994) Continuing Survey of Food Intakes by Individuals (CSFn): diet and health knowledge survey 1991. US Department of Commerce, National Technical Information Service, Springfield, VA (PB94500063: machine readable data set).
5. Bailey RL, Gahche JJ, Lentino CV, Dwyer JT, Engel JS, Thomas PR, Betz JM, Sempos CT, Picciano MF. Estimation of Total Usual Calcium and Vitamin D Intakes in the United States J. Nutr. 140: 817Ė822, 2010.
6. Prince R, Devine A, Dick I, Criddle A et al 1995 The effects of calcium supplementation (milk powder or tablets) and exercise on bone density in postmenopausal women. J Bone Miner Res 10:1068-1075
7. Tang BMP, Eslick GD, Nowson C, Smith C, Bensoussan A. 2007 Use of calcium or calcium in combination with Vitamin D supplementation to prevent fractures and bone loss in people aged 50 years and older: a meta-analysis. Lancet;370:657-66.
8. Chung M, Lee J, Terasawa T, Lau J, Trikalinos T. Vitamin D with or without calcium supplementation for prevention of cancer and fractures: an updated meta-analysis for the U.S. Preventive Services Task Force. Ann Intern Med. 2011;155(12):827-38.
9. Ross AC, Manson JE, Abrams SA, Aloia JF, Brannon PM, Clinton SK, Durazo-Arvizu RA, Gallagher JC, Gallo RL, Jones G, Kovacs CS, Mayne ST, Rosen CJ, Shapses SA. The 2011 Report on Dietary Reference Intakes for Calcium and Vitamin D from the Institute of Medicine: What Clinicians Need to Know. J Clin Endocrinol Metab. 2010 Nov 29. [Epub ahead of print]