to 30-year age range. This lower reported accretion rate is equivalent to a calcium accretion rate of only 6 mg/day. In addition to reporting only very small bone accretion for ages 19 through 30 years, Barger-Lux et al. (2005) also noted the possibility that there was no further effect on bone accretion above calcium intake levels of approximately 800 mg/day.
In short, bone accretion may continue during this early stage of adulthood, but at very low, almost indiscernible, levels. Interpretation of the data is further complicated by evidence from the Canadian Multicentre Osteoporosis Study (Berger et al., 2010), which demonstrates that attainment of peak bone mass depends upon which site is measured; peak bone mass is achieved by age 18 at some sites, but by age 25 or so at others. This newer population-based study is much larger than earlier studies, for example, Recker et al. (1992), and relies on the newer technique of DXA to estimate BMC. Tuck and Datta (2007) reported that maximal bone mass is attained in the second decade of life followed by a period of consolidation lasting 5 years, such that maximal levels are achieved in the early to mid 20s. Interestingly, peak trabecular bone mass is achieved earlier, at 15 to 18 years of age, is maintained for several years, and then begins to decline in young adulthood (Riggs et al., 2008).
Bone mineral content/bone mineral density: Calcium Measures of BMC and BMD in addition to calcium retention levels are also of interest as a measure of bone accretion. In a cross–sectional evaluation in 136 boys and men and 130 girls and women, including children beginning at the age of 4 years as well as adults through the age of 27 years, BMD of total body, lumbar spine, and femoral neck increased significantly with age until 17.5 years in boys and 15.8 years in girls (Lu et al., 1994). However, care must be taken in interpreting calcium intakes—specifically, calcium supplementation that results in total intakes above 1,500 mg/day for these groups—relative to BMC or BMD measures. Studies have suggested that increasing intakes of calcium in girls above their habitual intake of about 900 mg/day is associated with positive effects on bone mineral accretion and, in turn, BMD (Johnston et al., 1992; Lloyd et al., 1993; Chan et al., 1995). However, there is evidence that the bone mass gained through calcium or milk supplementation during childhood and adolescence is not retained post-intervention, suggesting that there is no benefit to intakes above that needed to ensure normal bone accretion (Fehily et al., 1992; Lee et al., 1996; Slemenda et al., 1997). A study conducted by Matkovic et al. (2004) evaluated BMD measures among female white adolescents 15 to 18 years of age in the United States, and reported that there was a positive influence of calcium supplementation and dairy products on BMD of the hip and forearm. The background level of calcium intake was approximately 833 mg/day, whereas the supplemented subjects had total calcium intakes of 1,586 mg/day. The Matkovic et al. (2004) study, however, did not follow