calcium supplementation on hypertension, blood pressure, or preeclampsia (Levine et al., 1997), perhaps because the intake of the control group was above a threshold value. In that study, women in the placebo group had a mean intake of 980 mg (24.5 mmol)/day and women in the supplemental calcium group had a mean intake of 2,300 mg (57.5 mmol)/day.
Because the effect of dietary calcium on blood pressure may be modest and variable in the general population, and because the calcium intake needed to reduce blood pressure is very likely below the threshold necessary for desirable skeletal retention (McCarron et al., 1991), blood pressure will not be used as a primary indicator for estimating calcium requirements.
Colon Cancer. Colon cancer risk has been postulated as being influenced by dietary calcium intake, but the evidence is inconsistent. Bostick and colleagues (1993) reported a reduction in mucosal proliferation after calcium supplementation, whereas Kleibeuker and colleagues (1993) reported an increase. Greater mucosal proliferation has been observed in patients known to be at high risk of colon cancer as compared with those at low risk (Kanemitsu et al., 1985; Ponz de Leon et al., 1988; Roncucci et al., 1991). Data from observational and case-control studies are mixed (Garland et al., 1985; Meyer and White, 1993; Slattery et al., 1988), and prospective trials examining the effect of added calcium on colon cancer incidence are not available. Thus, colon cancer incidence is not a useful indicator for estimating calcium requirements at this time.
In reviewing the scientific literature to provide the best estimate of calcium requirements for each stage of the lifespan, needed data were not always available. In most instances, calcium intake data could not be matched with the outcome criteria of both calcium retention and bone mass in the same subjects. For many of the age groups, available data did not adequately represent both genders and various ethnic groups. Although lower fracture rates have been reported in African American adults compared to those estimated in Caucasian adults (Farmer et al., 1984; Kellie and Brody, 1990) and in men compared to women (Cummings et al., 1993; Melton et al., 1992), the implications for calcium intake requirements are not clear at the present time. Because there is no sound basis for assigning different intake values according to gender or race/ethnic groups, findings have been extrapolated from one gender group to