better data related to calcium intakes from supplements and the incidence of kidney stones or other relevant health outcomes, establishing a UL of 2,000 mg of calcium per day is justified and provides a reasonable degree of public health protection without overly restricting the intake of calcium (notably from calcium supplements) for both men and women. There is no apparent reason to conclude that men in this age group are more sensitive than women. Although one 1993 observational study does not support the potential for increased kidney stone formation with supplement use among men, public health protection warrants caution for this older group. Moreover, the value of 2,000 mg of calcium per day is also somewhat below the 3,000 mg/day associated with calcium-alkali syndrome among persons with waning kidney function, the only other potential indicator with an estimate of threshold levels for effect.
The new UL of 2,000 mg of calcium per day for persons 51 to 70 years of age and for persons more than 70 years of age is lower than the 1997 UL of 2,500 mg/day for these groups (IOM, 1997). The newer data related to kidney stone formation are the primary basis for the new UL. It is extremely difficult to reach the UL on the basis of food sources of calcium. Rather, the excess intake comes about from the use of calcium supplements. Special considerations about the use of high level calcium supplements and the timing of supplement intake are discussed in Chapter 8.
Although the LOAEL (which is also the UL, as described above) for older adults more than 50 years of age is established at 2,000 mg/day, it can only serve as a starting point for UL consideration for adults 19 to 50 years of age given the observations that kidney stone formation in younger adults does not appear to be driven by calcium supplement use, and, as a rule, calcium supplement use is not as prevalent among younger adults. However, kidney stone formation is notable among younger persons; as discussed previously, the incident rate is actually higher among younger adults than among older adults. Given the UL of 3,000 mg/day for calcium set for adolescents up to the age of 18 years (based on high rate of bone accretion) as well as the likelihood that younger adults are able to tolerate higher maximal levels of calcium than other adults for whom kidney function may be slowly decreasing, an interpolation approach is used to establish a UL of 2,500 mg/day for adults 19 to 30 and 31 to 50 years of age, based on the mid-point between the UL of 2,000 mg of calcium per day set for persons more than 50 years of age and the UL of 3,000 mg/day set for adolescents 14 to 18 years of age. Further, concerns about the