The uncertainties surrounding the reference value stem from reliance on primarily a single study. Although carefully carried out, the study included only white children. These newer data, however, provide the opportunity to identify an average requirement.
While there is evidence of minor bone accretion into early adulthood, the levels required to achieve this accretion—which appears to be site dependent—are very low. The goal, therefore, is intakes of calcium that promote bone maintenance and neutral calcium balance.
The report from Hunt and Johnson (2007) provides virtually the only evidence for these life stage groups. Based on a series of controlled calcium balance studies, they have established a calcium intake level of 741 mg/day to maintain neutral calcium balance. They further provide the 95 percent prediction interval around the level required for neutral calcium balance.
Other available measures that relate to bone maintenance include bone mineral density (BMD), but studies that measured bone mass concomitant to calcium intake are highly confounded by failures to control for other variables that impact bone mass and to specify a dose–response relationship. There is no evidence that intakes of calcium higher than those specified by Hunt and Johnson (2007) offer benefit for bone health in the context of bone maintenance for adults 19 to 50 years of age. Osteoporotic fracture is not a relevant measure for this life stage, therefore extrapolating from the more prevalent data focused on older adults is not appropriate, nor is extrapolating from the data for younger persons for whom the concern is bone accretion.
Therefore, the Hunt and Johnson (2007) data, which reflect the outcomes of a series of metabolic studies, provide a reasonable basis for an EAR for calcium of 800 mg/day calcium. That is, the observed value of 741 mg/day is rounded, but rounded up to 800 mg/day given the uncertainty. The upper limit of the 95 percent prediction interval around this estimate (1,035 mg/day) is appropriate as the basis for an RDA for calcium and rounded to 1,000 mg/day. As is the case with younger life stage groups, there is now the 2007 Hunt and Johnson study on the topic of calcium and bone health, which has allowed the estimation of an average requirement.