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DRI DIETARY REFERENCE INTAKES FOR Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride
(Marshall et al., 1976). Calcium balance and usual calcium intake were positively correlated in 41 estrogen-deprived postmenopausal women with a mean usual calcium intake of 659 296 mg (16.5 ± 7.4 mmol)/day (Heaney and Recker, 1982; Heaney et al., 1977). In 76 women aged 50 to 85 years balance became more positive as calcium intake increased from 650 to 830 mg (16.2 to 20.7 mmol)/day (Ohlson et al., 1952). Only 10 women in that study had self-selected dietary calcium intakes over 1,000 mg (25 mmol)/day. Collectively, these studies consistently demonstrate that postmenopausal women with dietary calcium intakes under 1,000 mg (25 mmol)/day have less calcium loss when they increase their calcium intake.
Only two balance studies in postmenopansal women with average usual calcium intakes higher than 1,000 mg (25 mmol)/day were identified. Balance studies performed in 85 women with vertebral osteoporosis, aged 48 to 77 years, on a mean self-selected calcium intake of 1,116 mg (27.9 mmol)/day showed generally improved calcium balance in those subjects with higher calcium intakes (Hasling et al., 1990); very few subjects in this study had calcium intakes above 1,500 mg (37.5 mmol)/day. Calcium balance in 18 women and 7 men with osteoporosis (aged 26 to 70, mean 53 years) who consumed an average of 1,214 mg (30.3 mmol)/day of calcium was higher in those with higher calcium intakes (Selby, 1994). Notably, the men and women appeared to fit along the same regression line when intake was related to balance.
Several conclusions can be drawn from these balance studies. First, it is difficult to determine if the calcium intake needed for men over age 50 to minimize calcium loss is below 1,200 mg (30 mmol)/day as few studies have been done with intakes between 800 and 1,200 mg (20 and 30 mmol)/day. Second, available balance data indicate that the intake requirement of women over age 50 is at least 1,000 mg (25 mmol)/day and no evidence indicates that it differs substantially from that of similarly aged men. Finally, there are too few balance data at high calcium intakes to allow examination of subgroups, such as women in early menopause or subjects with and without fractures.
Bone Mineral Density. Many randomized, controlled, calcium intervention trials have been conducted in postmenopausal women. Several investigators have studied women within the first 5 years of menopause (designated as early postmenopausal), the period of most rapid bone loss (Aloia et al., 1994; Dawson-Hughes et al., 1990; Elders et al., 1991; Prince et al., 1995; Riis et al., 1987). Others have studied older or late postmenopausal women (Chevalley et al., 1994;