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DRI Dietary Reference Intakes Calcium Vitamin D
consume calcium supplements, is 2,000 mg/day, which is relatively close to the EAR and RDA values. For these more vulnerable groups, supplements containing amounts less than the RDA may be appropriate given that their diet is likely to contain at least some calcium. Further, until better information is available to clarify the possible link between supplement use and kidney stone formation, taking calcium supplements with foods is advisable.
Moreover, in the case of persons prone to developing kidney stones who cannot get adequate calcium from diet (e.g., due to lactose intolerance), there is limited evidence from small, short-term trials suggesting that supplemental calcium in moderate doses may not increase risk for stone recurrence (Levine et al., 1994; Williams et al., 2001; Lewandowski and Rodgers, 2004). Again, taking supplements with food is desirable.
The ULs are defined for the healthy, general population. Nonetheless, gray areas are acknowledged to exist between healthy people and those with medical conditions; for some persons in these gray areas a calcium intake as high as the UL may no longer be considered without any risk. The effect of calcium intake in situations of hypercalciuria is not fully understood, but conditions leading to hypercalciuria (which may be exacerbated by adding extra vitamin D to an already high calcium intake) may warrant a more cautious approach to ULs for calcium in the future. In older adults experiencing illness or decline, hypercalciuria may develop. For pregnant women experiencing absorptive hypercalciuria and therefore at higher risk of renal stone formation, keeping calcium intake below the UL may also be most appropriate. Similarly, as lactation drives bone resorption, urinary calcium excretion decreases, the ionized serum calcium concentration rises slightly, intravascular volume is contracted and occasionally women become hypercalcemic. Under these and similar conditions, ensuring a calcium intake below the UL may be most appropriate. Greater surveillance of urinary calcium excretion in future studies may shed more light on the relationship between higher levels of total calcium intake and risk of hypercalciuria or hypercalcemia under special conditions.
Oral Contraceptive Use
The use of ethinyl estradiol oral contraceptives (OCs) has been hypothesized to reduce bone resorption and preserve bone density in premenopausal and postmenopausal women. This concept was based on clinical and observational evidence that ethinyl estrogen–based hormone replacement therapy reduced risk for osteoporosis in postmenopausal women (Zittermann, 2000). A non-systematic review of clinical trials carried out before 1994 indicated that the evidence at that time largely supported positive effects of OCs on bone density in postmenopausal women, although a number of trials in the review showed no effects (DeCherney,