Calcium is the most abundant mineral found in bone and comprises approximately 33% of bone mineral. Optimal calcium intakes are essential across the life cycle to meet the daily intrinsic requirements of calcium required for skeletal growth and to offset urinary, dermal, and endogenous fecal calcium losses. When dietary intakes of calcium are not sufficient to maintain circulating calcium concentrations and/or when the losses of calcium from the body are excessive, bone calcium will be resorbed to maintain calcium homeostasis. Because calcium is essential for the structural integrity of bone, deficiencies or inadequate intakes of this mineral will have a detrimental impact on bone mass and quality. Skeletal mass peaks at approximately age 20�30 years, with much of this gain occurring during the pubertal growth spurt. Nearly 50% of adult bone mass is accumulated during the pubertal growth spurt. Thus, this period of skeletal accretion can be viewed as a window of opportunity to maximize skeletal mass. Calcium supplementation studies in children have found increased bone mass with supplementation, an effect that is most pronounced when implemented during the prepubertal period. It is not clear to what degree calcium supplementation during the pubertal growth spurt results in a net gain in peak bone mass or if it solely influences the tempo at which peak bone mass is achieved. To account for the importance of this nutrient in bone mineralization, the recommended adequate intake of calcium is highest (1300mg or 2.5mmol.day) between the ages of 9 and 18 years. Calcium supplementation has also been found to have beneficial effects on bone health in adults and may have the greatest impact in individuals whose habitual dietary calcium intakes are less than 400 mg (10mmol)/day. To account for a decreased efficiency of intestinal absorption coupled with increased losses of calcium in older individuals, recommended calcium intakes increase to 1200 mg (30mmol)/day in those age 50 or older. As discussed in more detail later, due to the prevalence of vitaminD deficiency in the elderly, oral vitamin D supplements up to 800 IU/day may also be required in order for the impact of calcium supplementation to be evident. Several epidemiological studies have found significant relationships between an individual's lifelong intake of milk and subsequent risk of fracture. The degree to which this effect is a consequence of increased calcium intake or due to other nutritional components of milk and dairy products requires further study. Despite the importance of calcium in bone mineral acquisition and maintenance, calcium intakes fall below the recommended level for the majority of age groups, with intake being particularly low for adolescent girls and adult and elderly women. It is often difficult to increase consumption of calcium in certain age groups due to low intakes of dairy products or to other factors, such as lactose intolerance, dieting, or altered appetite and food consumption patterns in groups such as the elderly. To increase the calcium content of the diet, nonfat milk powder yogurt or cheese, can be added to a number of recipes to increase the calcium content of the food without adversely affecting taste. An increasing variety of calcium-fortified food products are now also available. Individuals with lactose intolerance may improve intake of calcium by use of lactose-free dairy products or lactase pills. Increasing calcium intake from dietary versus supplemental sources also increases the intake of many other nutrients needed for bone health, including protein, magnesium, zinc, phosphorus, and vitamin D. For this reason, dietary approaches to increase calcium intake should be promoted over the use of calcium supplements alone. Despite these benefits, in some instances it may be necessary to utilize calcium supplements to achieve recommended intake levels. Several forms of calcium supplements are commercially available. Existing supplemental forms differ slightly with respect to their relative calcium content per tablet and their absorbability; however, the magnitude of these differences is minor and may not be biologically significant. Caution should be used when relying on natural sources of calcium (such as those prepared from bone meal, limestone, or oyster shells) because these preparations may also contain heavy metals such as lead. Several calcium supplements also contain additional nutrients required for bone health, including vitamins D and K. Because the fraction of calcium absorbed falls as calcium intake increases, little additional benefit per dose is achieved when taking supplemental calcium sources containing more than 500mg (12.5mmol) per dose.