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DRI Dietary Reference Intakes Calcium Vitamin D
confidence interval [CI]:0.83–0.95), but significant, effect on fracture risk reduction. In breaking down the meta-analysis further, there were six studies of more than 1,100 women with a mean age of 60 years who received additional calcium without vitamin D compared with placebo. The average calcium supplementation was 1,100 mg/day in the treated group, and those women had risk reduction for hip fracture and significant increases in both hip and spine BMD.
Further, evidence from the Women’s Health Initiative trial (WHI) (Jackson et al., 2006) conducted using 36,282 women ages 50 to 79 years indicated that participants who were randomized to 1,000 mg of calcium plus 400 International Units (IU) of vitamin D per day experienced a small, but significant, improvement in hip bone density and a modest reduction in hip fractures, although the change in hip fracture risk was not statistically significant. A subgroup analysis indicated that women over the age of 60 years also experienced a small but statistically non-significant reduction in hip fracture risk (hazard ratio [HR] = 0.74; 95 percent CI 0.52–1.06) compared with those randomized to placebo. These data are taken into account cautiously for several reasons. The WHI study may be confounded by both hormone replacement therapy considerations as well as the inclusion of vitamin D, although the supplementation level of vitamin D was relatively low. The appropriateness of conducting a subgroup analysis for fracture risk, although interesting, is always considered questionable. Further, the same subgroup analysis revealed that women between the ages of 50 and 60 years experienced a greater hip fracture risk when they were supplemented with calcium and vitamin D. The absolute risk of hip fractures for women 50 to 60 years of age is derived from a small number of fractures per total cohort (i.e., 13 fractures in 6,694 women 50 to 60 years of age). The Tang et al. (2007) meta-analysis is compromised by the inability to study a true dose–response relationship; many studies were grouped at the 1,200 mg/day level of intake and could not be used to reveal the effects at lower levels of intake.
Within the confines of these limitations, there is nonetheless the emerging conclusion that in regard to the relevant indicator for this group, that is, BMD, a somewhat higher intake of calcium than required by men or suggested by the newer calcium balance data is justified for all postmenopausal women within the life stage 51 through 70 years. Not unexpectedly, absolute hip fracture rates are very low in the 50- to 60-year age group (e.g., 0.03 percent per year in WHI), and therefore fracture risk is not a particularly relevant factor, although to the extent that a subgroup analysis can be relied upon, women greater than 60 years of age appear to experience some benefit from calcium intake relevant to fracture risk reduction.
It would appear that the life stage consisting of women 51 through